Re: [AMRadio] AM Usage with Linear AMPS
Mike, Ain't that exactly what I said 'way back at the very beginning of this thread...?! Hi Hi :>) ~73~ Eddy VE3CUI - VE3XZ - Original Message - From: "Mike Dorworth,K4XM" <[EMAIL PROTECTED]> To: "Discussion of AM Radio" Sent: Wednesday, November 24, 2004 8:14 PM Subject: Re: [AMRadio] AM Usage with Linear AMPS > QST for February 1956 in the Technical Topics section has a nice three page > write up on the use of Linear Amplifiers for AM. It starts on page 39. > > " This leads to the rule of thumb that on a.m. the carrier power output > that can be obtained from a linear amplifier is equal to half the rated > dissipation of the tube(s)." > > > __ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net >
Re: [AMRadio] AM Usage with Linear AMPS
QST for February 1956 in the Technical Topics section has a nice three page write up on the use of Linear Amplifiers for AM. It starts on page 39. " This leads to the rule of thumb that on a.m. the carrier power output that can be obtained from a linear amplifier is equal to half the rated dissipation of the tube(s)."
Re: [AMRadio] AM Usage with Linear AMPS
Donald Chester wrote: It doesn't get any better either. With modulation the dissipation does not decrease even though the efficiency increases at the peak power levels. The carrier power is still there 100% of the time at 30% efficiency. The audio is in the form of separate side bands that is additional power that the tube has to handle. Actually, it should get better. A properly operating amplifier with low level modulation, linear or grid modualted, should run a steady carrier output level and a constant DC input level, regardless of modulation. For the sake of discussion, let us assume 100 watts carrier output. The DC input will be about 300 watts @ roughly 30@ efficiency. With no modulation present, we have 300 watts input with 100 watts output. That leaves 200 watts dissipated in the tube plates. Now let's modulate 100% with a sinewave tone. The average rf power output will now be 150 watts, 100 watts carrier power plus 50 watts average sideband power. The DC input is still 300 watts, so the tubes are now dissipating only 150 watts as opposed to 200 watts with no modulation. The overall efficiency of the amplifier rises from 30% to 50%. If the tube plates are showing a glow, they should actually dim a little with modulation. Of course, the instantaneous efficiency is constantly varying over each cycle of the envelope waveform, from 0% at no output, to approximately 60% at maximum peak output capability of the amplifier. But it is AVERAGE power that determines how red the tube plates get, how loud the signal sounds over the air, and how much interference the signal produces. That is why the FCC's method of determining power output by p.e.p. is bogus. Don K4KYV Don, You are exactly right. I stand corrected. I remember that grid modulation are sometimes referred to as "variable efficiency modulation". The same principle applies to linear amplifiers with AM. When reducing power out to 1/4 as required for linear amplification the efficiency must drop to 1/2 of what it was at full carrier. At 100% modulation where 1/2 again as much power is in the output due to the audio, the efficiency also increases by 1/2 again as it is with only carrier. Like you said, the additional output comes from the plate dissipation as the input power stays the same. You rounded your numbers a little so the math does not come out exact in your example. But for those who wish to do their own: If an amp has 60% efficiency at full carrier reducing the output to 1/4 carrier will run it at 30% efficiency for the carrier. (exactly 1/2 the efficiency) 100% modulation will produce 50% more output and the efficiency will increase by 50% to 45%. (This is with a sine for modulation) These efficiency ratios must be maintained for linear operation. If the drive to the amp is not reduced to where the efficiency drops in half with the carrier, you will not be able to obtain 100% modulation without clipping in the amp. This is why you don't want to re-peak the output tuning on the amp when you reduce the drive. You change the efficiency when you retune. The carrier efficiency must be maintained at 1/2 the efficiency of full carrier which is the same level that modulation peaks will hit at full modulation. Orr explains it very nicely in the Radio Handbook in the modulation section. 73 Gary K4FMX
Re: [AMRadio] AM Usage with Linear AMPS
It doesn't get any better either. With modulation the dissipation does not decrease even though the efficiency increases at the peak power levels. The carrier power is still there 100% of the time at 30% efficiency. The audio is in the form of separate side bands that is additional power that the tube has to handle. Actually, it should get better. A properly operating amplifier with low level modulation, linear or grid modualted, should run a steady carrier output level and a constant DC input level, regardless of modulation. For the sake of discussion, let us assume 100 watts carrier output. The DC input will be about 300 watts @ roughly 30@ efficiency. With no modulation present, we have 300 watts input with 100 watts output. That leaves 200 watts dissipated in the tube plates. Now let's modulate 100% with a sinewave tone. The average rf power output will now be 150 watts, 100 watts carrier power plus 50 watts average sideband power. The DC input is still 300 watts, so the tubes are now dissipating only 150 watts as opposed to 200 watts with no modulation. The overall efficiency of the amplifier rises from 30% to 50%. If the tube plates are showing a glow, they should actually dim a little with modulation. Of course, the instantaneous efficiency is constantly varying over each cycle of the envelope waveform, from 0% at no output, to approximately 60% at maximum peak output capability of the amplifier. But it is AVERAGE power that determines how red the tube plates get, how loud the signal sounds over the air, and how much interference the signal produces. That is why the FCC's method of determining power output by p.e.p. is bogus. Don K4KYV
Re: [AMRadio] AM Usage with Linear AMPS
Geoff/W5OMR wrote: When you tune up you tune it for max output at the 200 watt level with full drive. At that tune setting the tube will be around 60% efficient. Assuming Class C about 60 to 70% yes. No. Class C is typically 70 to 75%. 60 to 65% is more likely for linear (AB1/AB2) operation. I have run a P&H Linear amplifier at these levels and even the 837s didn't glow red. But it may have been a little below 200 watts carrier. I only had it for a few weeks so it would not be a fair test. Thanks for explaining it in more detail for me. I just remember QST articles where a single 811A was run at 200 watts input as a linear amplifier or CW final and it did fine. The QST articles were probably talking about SSB or CW out of a single 811A at the 200w area. More than likely, it AM wasnn't considered in that test (*noting that QST is a publication of the ARRL, who would for a l-o-n-g time would NOT recognize AM as a valid mode of operation.) Maybe it was more than 30% efficient... that part still mystifies me! Sometimes I am dense though. Plate Voltage (Ep) * Plate Current (Ip) = DC Input. So, your quad 811A amp is running 1500v @ 400mA, you're running 600w DC input to the final. 150W per tube. That's to the max. When you tune the amp up for AM operation, leaving the amp at that -exact- tuning range, reduce the drive until you see only 150w, and probably a little less, to handle any asymmetry/transients in your voice*. 150W, modulated to 100% is around 600wPEP, but we're still talking DC INPUT, when you look at the 150W. So, 150 * 60% = around 90w of carrier output, which would be around 360W PEP output. Your mileage may vary, depending on Ep and Ip. If you just -have- to run a linear amplifier, instead of building up a plate modulated rig, at a MUCH higher efficiency rating, then build something with BIG tubes in it, that would handle the dissipation. like a pair of (or 3) 450TH's. 450W of plate dissipation, each. That'd bring you back up to the 1.5kW PEP level. That just might be a nice project... I could make a quad 450TL amp, and drive it with my Kenwood TS-680S I use mobile. (what a waste of a good tube!) 73 = Best Regards, -Geoff/W5OMR When you reduce the drive for AM operation you want to reduce the OUTPUT to 1/4 power, not the input power. The input power will be somewhere around 1/2 of full power when properly setup for AM. 73 Gary K4FMX
RE: [AMRadio] AM Usage with Linear AMPS
It is only SSB, but I used it to talk to all my buds on 75 and 40 while on trips across the US. I expected more than 150 watts out hen I whistled in the mike. John, WA5BXO -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Brian Carling Sent: Tuesday, November 23, 2004 6:25 AM To: Discussion of AM Radio Subject: RE: [AMRadio] AM Usage with Linear AMPS I thought that the WRL DuaoBander mobile was only SSB. On 22 Nov 2004 at 22:11, John Coleman, ARS WA5BXO wrote: > My experience (which is very little when it come to these sweep tube > rigs) is they or rated for a belch or some thing short and don't hold up > to a fix channel field day adventure with out tube replacement. I had a > DuaoBander mobile for a while rated a 400 watts PEP input I never saw > more than 150 watts output while whistling in the mike. It was in > perfect condition and would light a 50 watt bulb with normal speech. I > thought it would have blown it out. I was very disappointed. Yet, it > was one of the most heard radios all over the country by many AMers in > the late 80s. > > > John, WA5BXO > > > -Original Message- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Brian Carling > Sent: Monday, November 22, 2004 9:55 PM > To: Discussion of AM Radio > Subject: RE: [AMRadio] AM Usage with Linear AMPS > > Aren't there a lot of commercially built amateur radio linear > amplifiers and RF finals that exceeded he manufacturers MAX > Pdiss rathings over the years, by adding a COOLING FAN to take > away the extra heat? > > One thinks of MANY sweep tubes rated for so-called Pdiss of 16 > watts and 20 watts that are regularly run at hundreds of watts of > RF! The tubes don't seem to melt. > > I think of the ubiquitous 6JS6C with a rating of 30 watts. > Yaesu ran a pair of these at 260 watts input in their FT101 series. > Many guys ran them at 260 watts p.e.p. on SSB and 260 watts CW. > Assuming 65% efficiency, you have 35% of 260 watts going into > the plates. That is to say 91 watts split between the two tubes. > UH oh - POP! But no, they didn't. > > Then when you throttle that FT-101 back to 40 watts input on AM > and go to your 30% efficiency (if it is) then you are actually > putting only 20 watts carrier per tube which is SAFER. > > Is that correct? > > How about some of the othre rigs that rated their 2 sweep tube > finals for 560 Watts or even 800 watts!? > > Then youhave peak Pdisses of 140 to 200 watts between the two > sweep tubes, most of which are rated for no more than 40 watts. > > > > > > __ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net __ AMRadio mailing list Home: http://mailman.qth.net/mailman/listinfo/amradio Help: http://mailman.qth.net/mmfaq.html Post: mailto:AMRadio@mailman.qth.net
Re: [AMRadio] AM Usage with Linear AMPS
- Original Message - From: "Brian Carling" <[EMAIL PROTECTED]> To: "Discussion of AM Radio" Sent: Tuesday, November 23, 2004 6:25 AM Subject: RE: [AMRadio] AM Usage with Linear AMPS > I thought that the WRL DuaoBander mobile was only SSB. it is. > > On 22 Nov 2004 at 22:11, John Coleman, ARS WA5BXO wrote: > > > My experience (which is very little when it come to these sweep tube > > rigs) is they or rated for a belch or some thing short and don't hold up > > to a fix channel field day adventure with out tube replacement. I had a > > DuaoBander mobile for a while rated a 400 watts PEP input I never saw > > more than 150 watts output while whistling in the mike. It was in > > perfect condition and would light a 50 watt bulb with normal speech. I > > thought it would have blown it out. I was very disappointed. Yet, it > > was one of the most heard radios all over the country by many AMers in > > the late 80s. I was one of the AM'ers that heard his SSB mobile, wherever he was, from Texas to Virginia, regardless of Band, or time of day. That rig WORKED, and the Antenna... geeze... a work of ART! :-) 73 = Best Regards, -Geoff/W5OMR
Re: [AMRadio] AM Usage with Linear AMPS
- Original Message - From: "John Coleman, ARS WA5BXO" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]>; "'Discussion of AM Radio'" Sent: Monday, November 22, 2004 10:11 PM Subject: RE: [AMRadio] AM Usage with Linear AMPS > My experience (which is very little when it come to these sweep tube > rigs) is they or rated for a belch or some thing short and don't hold up > to a fix channel field day adventure with out tube replacement. I had a > DuaoBander mobile for a while rated a 400 watts PEP input I never saw > more than 150 watts output while whistling in the mike. It was in > perfect condition and would light a 50 watt bulb with normal speech. I > thought it would have blown it out. I was very disappointed. Yet, it > was one of the most heard radios all over the country by many AMers in > the late 80s. Well, yeah... when you had the Q of the antenna at about 50, or so ;-) 73 = Best Regards, -Geoff/W5OMR
Re: [AMRadio] AM Usage with Linear AMPS
On 22 Nov 2004 at 23:40, [EMAIL PROTECTED] wrote: > Yaesu's instructions were "don't hold key down for more than 10 sec on > tune > up!" Otherwise - POP! Voice is a low duty cycle signal. In SSB > service > the average dissipation level can be kept within reasonable limits unless > heavy > voice processing is involved. > > > Then when you throttle that FT-101 back to 40 watts input on AM > > and go to your 30% efficiency (if it is) then you are actually > > putting only 20 watts carrier per tube which is SAFER. > > > > Is that correct? > > > > > Actually, on AM the FT-101 is throttled back to something like 100 W > INPUT, > 25 - 30 W carrier OUTPUT. Optional fan recommended. My FT-101E performed very well for me on AM. 40 watts carrier input the best I remember.
RE: [AMRadio] AM Usage with Linear AMPS
I thought that the WRL DuaoBander mobile was only SSB. On 22 Nov 2004 at 22:11, John Coleman, ARS WA5BXO wrote: > My experience (which is very little when it come to these sweep tube > rigs) is they or rated for a belch or some thing short and don't hold up > to a fix channel field day adventure with out tube replacement. I had a > DuaoBander mobile for a while rated a 400 watts PEP input I never saw > more than 150 watts output while whistling in the mike. It was in > perfect condition and would light a 50 watt bulb with normal speech. I > thought it would have blown it out. I was very disappointed. Yet, it > was one of the most heard radios all over the country by many AMers in > the late 80s. > > > John, WA5BXO > > > -Original Message- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Brian Carling > Sent: Monday, November 22, 2004 9:55 PM > To: Discussion of AM Radio > Subject: RE: [AMRadio] AM Usage with Linear AMPS > > Aren't there a lot of commercially built amateur radio linear > amplifiers and RF finals that exceeded he manufacturers MAX > Pdiss rathings over the years, by adding a COOLING FAN to take > away the extra heat? > > One thinks of MANY sweep tubes rated for so-called Pdiss of 16 > watts and 20 watts that are regularly run at hundreds of watts of > RF! The tubes don't seem to melt. > > I think of the ubiquitous 6JS6C with a rating of 30 watts. > Yaesu ran a pair of these at 260 watts input in their FT101 series. > Many guys ran them at 260 watts p.e.p. on SSB and 260 watts CW. > Assuming 65% efficiency, you have 35% of 260 watts going into > the plates. That is to say 91 watts split between the two tubes. > UH oh - POP! But no, they didn't. > > Then when you throttle that FT-101 back to 40 watts input on AM > and go to your 30% efficiency (if it is) then you are actually > putting only 20 watts carrier per tube which is SAFER. > > Is that correct? > > How about some of the othre rigs that rated their 2 sweep tube > finals for 560 Watts or even 800 watts!? > > Then youhave peak Pdisses of 140 to 200 watts between the two > sweep tubes, most of which are rated for no more than 40 watts. > > > > > > __ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net
RE: [AMRadio] AM Usage with Linear AMPS
VERY fascinating... yes, this does support the descriptions of 811A Pdiss in AM linear mode. I wonder if you could use ceramic insulators instead of lucite and keep things cooler? On 22 Nov 2004 at 22:04, Jim candela wrote: > > > Gary, > > I like your analysis on the topic. Brian may be looking for hard data to > back up the theoretical. I recently finished a single EL-34 (6CA7) Class AB2 > RF linear amplifier in a Central electronics 20a. In my case I got only 20% > efficiency on AM! I am going to present some data achieved on 80 meters > here: > > Condition Maximum CW output: > > Power Output 40 watts > Plate Voltage 615 v > Screen voltage 300 v > Screen current 30ma > Cathode current 178 ma > DC plate input power 91 watts > Plate circuit efficiency 44% > Plate dissipation 51 watts* > > Condition ready for AM modulation: > > Power Output 8 watts > Plate Voltage 636 v > Screen voltage 309 v > Screen current 11 ma > Cathode current 74 ma > DC plate input power 40 watts > Plate circuit efficiency 20% > Plate dissipation 32 watts* > > Keep in mind that the CCS EL-34 plate dissipation rating is 25 watts. With > forced air cooling, and brief full power tune ups, the Russian tube behaves > pretty well considering the abuse I am giving it. The tube plate does show > some red however on AM, and even more at maximum CW output. This example of > an overloaded EL-34 is somewhat similar to the overloaded 811 in earlier > examples in this email thread. > > I had circuit variations that offered increased power and efficiency at the > expense of linearity. With this tube, getting good linearity on AM (seen on > trapezoid pattern on scope) resulted in a pretty hot tube. I even added > feedback where I rectified the RF output, obtained audio and sent that back > to the speech amp for audio inverse feedback. That technique works extremely > well. > > * This includes losses in the output coupling circuit; the Lucite strips > securing the tank coil tend to soften and droop at 50 watts RF output when > on 160 meters. Maybe I actually am getting closer to 30% PLATE efficiency on > AM. > > Regards, > Jim Candela > WD5JKO > > -Original Message- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] Behalf Of Gary Schafer > Sent: Monday, November 22, 2004 9:23 PM > To: [EMAIL PROTECTED]; Discussion of AM Radio > Subject: Re: [AMRadio] AM Usage with Linear AMPS > > > Brian, > > What he is saying is: you need to have the 811A tuned up at 200 watts > output on cw or pep for a 50 watt carrier out. (pep is 4 times carrier) > > When you tune up you tune it for max output at the 200 watt level with > full drive. At that tune setting the tube will be around 60% efficient. > Normal ssb or cw operation tune-up. input power will be 333 watts. The > tube will be dissipating 133 watts in heat at full carrier. > > You then reduce the drive until you have 50 watts out (1/4 the carrier > of full output). You can not retune at this point or it will not handle > the peak envelope power of 4 times carrier. At 50 watts out the > efficiency drops to around 30%. So that means to get the 50 watts out > the tube has to be running around 150 watts input. 150 watts minus the > 50 watts output leaves 100 watts to dissipate in heat in the plate as > long as the carrier is on. > > It doesn't get any better either. With modulation the dissipation does > not decrease even though the efficiency increases at the peak power > levels. The carrier power is still there 100% of the time at 30% > efficiency. The audio is in the form of separate side bands that is > additional power that the tube has to handle. > > I guarantee you that an 811A will run with a red plate under these > conditions. If it is not red then it is not tuned up properly for this > mode of operation at the 50 watt carrier out level. > > 73 > Gary K4FMX > > > > > Brian Carling wrote: > > On 22 Nov 2004 at 20:23, [EMAIL PROTECTED] wrote: > > > > > >>Going to shorten it's life considerably. > > > > > > Theoretically maybe. Have you tried it. How can you know > > for sure? Theory says a bumble bee can't fly. My 811A tubes > > never burned up. > > > > Where did you get your 30% number from? Who transmits > > their AM with carrier only!? I can't see how a 50 watt carrier input > > will cause an 811A to DISSIPATE 100 watts! > > Where are you getting the additional 50? > > > > > >>To properly adjust a linear amp for AM it is necessary to tune the thing > up for the peak power > >>level, i.e., 200 watts for a 50W carrie
Re: [AMRadio] AM Usage with Linear AMPS
> > When you tune up you tune it for max output at the 200 watt level with > > full drive. At that tune setting the tube will be around 60% efficient. > > Assuming Class C about 60 to 70% yes. No. Class C is typically 70 to 75%. 60 to 65% is more likely for linear (AB1/AB2) operation. > I have run a P&H Linear amplifier at these levels and even the > 837s didn't glow red. But it may have been a little below 200 watts > carrier. I only had it for a few weeks so it would not be a fair test. > > Thanks for explaining it in more detail for me. > > I just remember QST articles where a single 811A was run at 200 > watts input as a linear amplifier or CW final and it did fine. The QST articles were probably talking about SSB or CW out of a single 811A at the 200w area. More than likely, it AM wasnn't considered in that test (*noting that QST is a publication of the ARRL, who would for a l-o-n-g time would NOT recognize AM as a valid mode of operation.) > Maybe it was more than 30% efficient... that part still mystifies me! > Sometimes I am dense though. Plate Voltage (Ep) * Plate Current (Ip) = DC Input. So, your quad 811A amp is running 1500v @ 400mA, you're running 600w DC input to the final. 150W per tube. That's to the max. When you tune the amp up for AM operation, leaving the amp at that -exact- tuning range, reduce the drive until you see only 150w, and probably a little less, to handle any asymmetry/transients in your voice*. 150W, modulated to 100% is around 600wPEP, but we're still talking DC INPUT, when you look at the 150W. So, 150 * 60% = around 90w of carrier output, which would be around 360W PEP output. Your mileage may vary, depending on Ep and Ip. If you just -have- to run a linear amplifier, instead of building up a plate modulated rig, at a MUCH higher efficiency rating, then build something with BIG tubes in it, that would handle the dissipation. like a pair of (or 3) 450TH's. 450W of plate dissipation, each. That'd bring you back up to the 1.5kW PEP level. That just might be a nice project... I could make a quad 450TL amp, and drive it with my Kenwood TS-680S I use mobile. (what a waste of a good tube!) 73 = Best Regards, -Geoff/W5OMR (*See: http://www.qsl.net/wa5bxo/asyam/aam3.html for more info on asymmetric voice patterns, and a few hams ideas for working WITH the 1500wPEP Output nonsensical FCC ruling.)
Re: [AMRadio] AM Usage with Linear AMPS
The plate efficiency at full output under practical conditionsis usually of the order of 50 to 65 per cent. With less than the full output, the efficiency is proportional to the driving voltage. When the signal to be amplified is a carrier wave modulated 100 per cent, the carrier amplitude is half the peak amplitude to be handled. The efficiency for the unmodulated wave is then half the maximum efficiency, or 25 to abour 32 per cent under ordinary conditions. The average efficiency of a linear amplifier used with amplitude-modulated waves is hence relatively low, because ordinarily the wave is fully modulated only a small part of the time; even when fully modulated, it is at or near the crest value for only a small fraction of the modulation cycle. The peak output power that can be developed by a tube operating as a linear amplifier is approximately the same as the power developed by the same tube in Class-C amplifier operation, or it may be slightly greater since the linear amplifier does not operate at peak level continuously. Since the peak power of a fully modulated wave is four times the carrier power, a tube used as a linear amplifier is capable of developing something between one-half and one-fourth as much carrier power as the output attainable from the same tube operated as a Class-C amplifier. -Terman A pair of 6146's operating at 600VDC put out 100 watts single tone. This is the maximum that amplifier would make. The current was about 260mA. peak/single tone: 600VDC * 260mA = 156 watts input. 100 out, 56 dissipation. 64% efficiency. Carrier conditions: 600VDC * 135mA = 81 watts input. 25 out, 56 dissipation. 31% efficiency. I realize this is pushing 6146's, better would have been 80 watts PEP and 20W carrier. The point is the efficiency as taken by meter readings. These values can probably be validated on a host of existing 2x 6146-equippped gear.
Re: [AMRadio] AM Usage with Linear AMPS
In a message dated 11/22/04 7:56:07 PM, [EMAIL PROTECTED] writes: > One thinks of MANY sweep tubes rated for so-called Pdiss of 16 > watts and 20 watts that are regularly run at hundreds of watts of > RF! The tubes don't seem to melt. > > I think of the ubiquitous 6JS6C with a rating of 30 watts. > Yaesu ran a pair of these at 260 watts input in their FT101 series. > Many guys ran them at 260 watts p.e.p. on SSB and 260 watts CW. > Assuming 65% efficiency, you have 35% of 260 watts going into > the plates. That is to say 91 watts split between the two tubes. > UH oh - POP! But no, they didn't. > Yaesu's instructions were "don't hold key down for more than 10 sec on tune up!" Otherwise - POP! Voice is a low duty cycle signal. In SSB service the average dissipation level can be kept within reasonable limits unless heavy voice processing is involved. > > Then when you throttle that FT-101 back to 40 watts input on AM > and go to your 30% efficiency (if it is) then you are actually > putting only 20 watts carrier per tube which is SAFER. > > Is that correct? > > Actually, on AM the FT-101 is throttled back to something like 100 W INPUT, 25 - 30 W carrier OUTPUT. Optional fan recommended. > How about some of the othre rigs that rated their 2 sweep tube > finals for 560 Watts or even 800 watts!? > Yes, the SWAN 750 for example. Had one in our Club back East. Be light on the key with this sucker or definitely POP! Dennis D. W7QHO Glendale, CA
Re: [AMRadio] AM Usage with Linear AMPS
Sweep tubes are a little different animal. They are designed for high peak power levels in TV sweep circuits. SSB has a pretty high peak to average power level. The average power is only in the order of 10 to 20% of pep. Unless you run heavy processing and then the sweep tubes will take a dive. They don't like AM very well either as the average power is much higher on AM. Tuning up an old swan at 500 watts you don't want to leave the carrier on very long. Tune quick and get rid of the carrier. There have been many sweep tubes cooked on tune up by being too slow twisting the knobs. 73 Gary K4FMX Brian Carling wrote: Aren't there a lot of commercially built amateur radio linear amplifiers and RF finals that exceeded he manufacturers MAX Pdiss rathings over the years, by adding a COOLING FAN to take away the extra heat? One thinks of MANY sweep tubes rated for so-called Pdiss of 16 watts and 20 watts that are regularly run at hundreds of watts of RF! The tubes don't seem to melt. I think of the ubiquitous 6JS6C with a rating of 30 watts. Yaesu ran a pair of these at 260 watts input in their FT101 series. Many guys ran them at 260 watts p.e.p. on SSB and 260 watts CW. Assuming 65% efficiency, you have 35% of 260 watts going into the plates. That is to say 91 watts split between the two tubes. UH oh - POP! But no, they didn't. Then when you throttle that FT-101 back to 40 watts input on AM and go to your 30% efficiency (if it is) then you are actually putting only 20 watts carrier per tube which is SAFER. Is that correct? How about some of the othre rigs that rated their 2 sweep tube finals for 560 Watts or even 800 watts!? Then youhave peak Pdisses of 140 to 200 watts between the two sweep tubes, most of which are rated for no more than 40 watts. On 22 Nov 2004 at 21:29, John Coleman, ARS WA5BXO wrote: I've got to get in on this HIHI. Some readers may not fully understand what you guys or talking about. So I will try to confuse it all some more. HIHI Plate dissipation is the heat that the plate of a tube is emitting. The manufacture of the tube has what is known as max plate dissipation limits. The 811A triode has a limit of about 65 watts. This means if the tube is in a circuit where it is putting out a steady carrier and this circuit is 75% efficient at is max level this would be 4 X 65 input power (Ep X Ip) and 3 X 65 output power (as measured by a RF Watt meter with no reflected power). This would be 260 watts input and 195 watts output with 65 watts wasted in heat of the plate. This would not be bad for CW. I don't think 75% efficiency is an achievable figure in a good linear operation even on peaks. As the drive level is reduced so is the output level (linearly we hope) but the plate current will not drop as fast. As a result the efficiency drops and it is possible for the plate dissipation to be greater even though the plate current is less. It is not a good idea to operate at the point where the plate dissipation is at its highest. In any linear amplifier audio or otherwise, proper design would be, to not exceed the plate dissipation at any time. How ever we all know that plate dissipation limits can be exceeded for a short duration provided that there is an equal or more amount of time that has a much less plate dissipation than the rating and that the time intervals or close enough to keep the overall temperature down on the tube. Exceeding Plate dissipation causes excessive secondary emissions and internal grid leakage. It is also the biggest cause of vacuum loss because of leaking seals at the anode connection. Poor vacuum causes more grid leakage and emission loss due to corroded heaters. Over temp on a tube is not good even for a short period of time. In a class B circuit with no input or output the plate dissipation must be below the limit. If the input is varying as it is with SSB or audio then the tube will pass through an area of much higher dissipation. This area is generally (but not always) somewhere near the 50% mark of peak drive and output. This means, the tube could actually be hot with just a carrier and, then cool down when the input is modulated with a tone. As I recall 811s do not (or just barely) show color at 65 watts dissipation. This would be static 2000V and 32 ma or 1500 volts and 43ma. Good practice would be to set bias some what below current for 65 watts dissipation. As input carrier is introduced a output carrier will also be created. It should be a linear progression until top end is met. During this progression the tube will go through various levels of efficiency and plate dissipation. Some of the places will be very close to or exceeding the limit of 65 watts. A point of best operation would be where the output is 25 % or less of the peak output POWER level (OR 50% of the RF output VOLTAGE) and the plate dissipation (input power
RE: [AMRadio] AM Usage with Linear AMPS
Gary, I like your analysis on the topic. Brian may be looking for hard data to back up the theoretical. I recently finished a single EL-34 (6CA7) Class AB2 RF linear amplifier in a Central electronics 20a. In my case I got only 20% efficiency on AM! I am going to present some data achieved on 80 meters here: Condition Maximum CW output: Power Output 40 watts Plate Voltage 615 v Screen voltage 300 v Screen current 30ma Cathode current 178 ma DC plate input power 91 watts Plate circuit efficiency 44% Plate dissipation 51 watts* Condition ready for AM modulation: Power Output 8 watts Plate Voltage 636 v Screen voltage 309 v Screen current 11 ma Cathode current 74 ma DC plate input power 40 watts Plate circuit efficiency 20% Plate dissipation 32 watts* Keep in mind that the CCS EL-34 plate dissipation rating is 25 watts. With forced air cooling, and brief full power tune ups, the Russian tube behaves pretty well considering the abuse I am giving it. The tube plate does show some red however on AM, and even more at maximum CW output. This example of an overloaded EL-34 is somewhat similar to the overloaded 811 in earlier examples in this email thread. I had circuit variations that offered increased power and efficiency at the expense of linearity. With this tube, getting good linearity on AM (seen on trapezoid pattern on scope) resulted in a pretty hot tube. I even added feedback where I rectified the RF output, obtained audio and sent that back to the speech amp for audio inverse feedback. That technique works extremely well. * This includes losses in the output coupling circuit; the Lucite strips securing the tank coil tend to soften and droop at 50 watts RF output when on 160 meters. Maybe I actually am getting closer to 30% PLATE efficiency on AM. Regards, Jim Candela WD5JKO -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Gary Schafer Sent: Monday, November 22, 2004 9:23 PM To: [EMAIL PROTECTED]; Discussion of AM Radio Subject: Re: [AMRadio] AM Usage with Linear AMPS Brian, What he is saying is: you need to have the 811A tuned up at 200 watts output on cw or pep for a 50 watt carrier out. (pep is 4 times carrier) When you tune up you tune it for max output at the 200 watt level with full drive. At that tune setting the tube will be around 60% efficient. Normal ssb or cw operation tune-up. input power will be 333 watts. The tube will be dissipating 133 watts in heat at full carrier. You then reduce the drive until you have 50 watts out (1/4 the carrier of full output). You can not retune at this point or it will not handle the peak envelope power of 4 times carrier. At 50 watts out the efficiency drops to around 30%. So that means to get the 50 watts out the tube has to be running around 150 watts input. 150 watts minus the 50 watts output leaves 100 watts to dissipate in heat in the plate as long as the carrier is on. It doesn't get any better either. With modulation the dissipation does not decrease even though the efficiency increases at the peak power levels. The carrier power is still there 100% of the time at 30% efficiency. The audio is in the form of separate side bands that is additional power that the tube has to handle. I guarantee you that an 811A will run with a red plate under these conditions. If it is not red then it is not tuned up properly for this mode of operation at the 50 watt carrier out level. 73 Gary K4FMX Brian Carling wrote: > On 22 Nov 2004 at 20:23, [EMAIL PROTECTED] wrote: > > >>Going to shorten it's life considerably. > > > Theoretically maybe. Have you tried it. How can you know > for sure? Theory says a bumble bee can't fly. My 811A tubes > never burned up. > > Where did you get your 30% number from? Who transmits > their AM with carrier only!? I can't see how a 50 watt carrier input > will cause an 811A to DISSIPATE 100 watts! > Where are you getting the additional 50? > > >>To properly adjust a linear amp for AM it is necessary to tune the thing up for the peak power >>level, i.e., 200 watts for a 50W carrier. The linear will be about 60% efficient at this output level. >>Then WITHOUT CHANGING THE TUNING adjust the output from the AM exciter to provide for >>50W out of the linear with no modulation. The problem here is that the linear will now only be >>running about 30% efficiency under carrier-only conditions and the 811 would be dissipating >>something like 100+ watts. The 811A, of course, is only rated at 65 watts. >> >>Dennis D. W7QHO >>Glendale, CA > > > > __ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net > > ___
RE: [AMRadio] AM Usage with Linear AMPS
Hi Brian: Consider what the efficiency is with no drive. The tube is drawing current and has voltage therefore it has input power but no output. Efficiency is 0%. As input drive is applied the efficiency increases but so does the plate current. The trick is to reach the 25% power point (or 50 Voltage point if monitoring on a scope) with out hitting the spot where the dissipation is 65 watts / 811A. John, WA5BXO
RE: [AMRadio] AM Usage with Linear AMPS
Aren't there a lot of commercially built amateur radio linear amplifiers and RF finals that exceeded he manufacturers MAX Pdiss rathings over the years, by adding a COOLING FAN to take away the extra heat? One thinks of MANY sweep tubes rated for so-called Pdiss of 16 watts and 20 watts that are regularly run at hundreds of watts of RF! The tubes don't seem to melt. I think of the ubiquitous 6JS6C with a rating of 30 watts. Yaesu ran a pair of these at 260 watts input in their FT101 series. Many guys ran them at 260 watts p.e.p. on SSB and 260 watts CW. Assuming 65% efficiency, you have 35% of 260 watts going into the plates. That is to say 91 watts split between the two tubes. UH oh - POP! But no, they didn't. Then when you throttle that FT-101 back to 40 watts input on AM and go to your 30% efficiency (if it is) then you are actually putting only 20 watts carrier per tube which is SAFER. Is that correct? How about some of the othre rigs that rated their 2 sweep tube finals for 560 Watts or even 800 watts!? Then youhave peak Pdisses of 140 to 200 watts between the two sweep tubes, most of which are rated for no more than 40 watts. On 22 Nov 2004 at 21:29, John Coleman, ARS WA5BXO wrote: > I've got to get in on this HIHI. > > Some readers may not fully understand what you guys or talking > about. > So I will try to confuse it all some more. HIHI > > Plate dissipation is the heat that the plate of a tube is > emitting. > The manufacture of the tube has what is known as max plate dissipation > limits. The 811A triode has a limit of about 65 watts. This means if > the tube is in a circuit where it is putting out a steady carrier and > this circuit is 75% efficient at is max level this would be 4 X 65 input > power (Ep X Ip) and 3 X 65 output power (as measured by a RF Watt meter > with no reflected power). This would be 260 watts input and 195 watts > output with 65 watts wasted in heat of the plate. This would not be bad > for CW. > > I don't think 75% efficiency is an achievable figure in a good linear > operation even on peaks. As the drive level is reduced so is the output > level (linearly we hope) but the plate current will not drop as fast. > As a result the efficiency drops and it is possible for the plate > dissipation to be greater even though the plate current is less. It is > not a good idea to operate at the point where the plate dissipation is > at its highest. > > In any linear amplifier audio or otherwise, proper design would be, to > not exceed the plate dissipation at any time. How ever we all know that > plate dissipation limits can be exceeded for a short duration provided > that there is an equal or more amount of time that has a much less plate > dissipation than the rating and that the time intervals or close enough > to keep the overall temperature down on the tube. Exceeding Plate > dissipation causes excessive secondary emissions and internal grid > leakage. It is also the biggest cause of vacuum loss because of leaking > seals at the anode connection. Poor vacuum causes more grid leakage and > emission loss due to corroded heaters. Over temp on a tube is not good > even for a short period of time. > > In a class B circuit with no input or output the plate > dissipation must be below the limit. > > If the input is varying as it is with SSB or audio then the tube > will pass through an area of much higher dissipation. This area is > generally (but not always) somewhere near the 50% mark of peak drive and > output. This means, the tube could actually be hot with just a carrier > and, then cool down when the input is modulated with a tone. > > As I recall 811s do not (or just barely) show color at 65 watts > dissipation. This would be static 2000V and 32 ma or 1500 volts and > 43ma. > > Good practice would be to set bias some what below current for > 65 watts dissipation. As input carrier is introduced a output carrier > will also be created. It should be a linear progression until top end > is met. During this progression the tube will go through various levels > of efficiency and plate dissipation. Some of the places will be very > close to or exceeding the limit of 65 watts. > > A point of best operation would be where the output is 25 % or > less of the peak output POWER level (OR 50% of the RF output VOLTAGE) > and the plate dissipation (input power - output power) is less that 65 > watts per 811A. > > Good Luck to all > John WA5BXO > > > > __ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net
Re: [AMRadio] AM Usage with Linear AMPS
On 22 Nov 2004 at 22:23, Gary Schafer wrote: > Brian, > > What he is saying is: you need to have the 811A tuned up at 200 watts > output on cw or pep for a 50 watt carrier out. (pep is 4 times carrier) AH ha - I thought we were talking INPUT. For 50 watts per tube to this Quad 811A amplifier, then I don't know why you would only get 30% efficiency but let's say you did. 50 watts out = about 166 watts input. That would mean 116 watts of dissipation per tube. I agree - it's excessive. Just not sure why it is 30% efficient. I was basing it on 50 watts INPUT per tube. > When you tune up you tune it for max output at the 200 watt level with > full drive. At that tune setting the tube will be around 60% efficient. Assuming Class C about 60 to 70% yes. > Normal ssb or cw operation tune-up. input power will be 333 watts. The > tube will be dissipating 133 watts in heat at full carrier. Hmmm where did I get 166 watts? > You then reduce the drive until you have 50 watts out (1/4 the carrier > of full output). You can not retune at this point or it will not handle > the peak envelope power of 4 times carrier. At 50 watts out the > efficiency drops to around 30%. Why? > So that means to get the 50 watts out > the tube has to be running around 150 watts input. 150 watts minus the > 50 watts output leaves 100 watts to dissipate in heat in the plate as > long as the carrier is on. > It doesn't get any better either. With modulation the dissipation does > not decrease even though the efficiency increases at the peak power > levels. The carrier power is still there 100% of the time at 30% > efficiency. The audio is in the form of separate side bands that is > additional power that the tube has to handle. But not dissipate, I guess... > I guarantee you that an 811A will run with a red plate under these > conditions. If it is not red then it is not tuned up properly for this > mode of operation at the 50 watt carrier out level. I have run a P&H Linear amplifier at these levels and even the 837s didn't glow red. But it may have been a little below 200 watts carrier. I only had it for a few weeks so it would not be a fair test. Thanks for explaining it in more detail for me. I just remember QST articles where a single 811A was run at 200 watts input as a linear amplifier or CW final and it did fine. Maybe it was more than 30% efficient... that part still mystifies me! Sometimes I am dense though.
RE: [AMRadio] AM Usage with Linear AMPS
I've got to get in on this HIHI. Some readers may not fully understand what you guys or talking about. So I will try to confuse it all some more. HIHI Plate dissipation is the heat that the plate of a tube is emitting. The manufacture of the tube has what is known as max plate dissipation limits. The 811A triode has a limit of about 65 watts. This means if the tube is in a circuit where it is putting out a steady carrier and this circuit is 75% efficient at is max level this would be 4 X 65 input power (Ep X Ip) and 3 X 65 output power (as measured by a RF Watt meter with no reflected power). This would be 260 watts input and 195 watts output with 65 watts wasted in heat of the plate. This would not be bad for CW. I don't think 75% efficiency is an achievable figure in a good linear operation even on peaks. As the drive level is reduced so is the output level (linearly we hope) but the plate current will not drop as fast. As a result the efficiency drops and it is possible for the plate dissipation to be greater even though the plate current is less. It is not a good idea to operate at the point where the plate dissipation is at its highest. In any linear amplifier audio or otherwise, proper design would be, to not exceed the plate dissipation at any time. How ever we all know that plate dissipation limits can be exceeded for a short duration provided that there is an equal or more amount of time that has a much less plate dissipation than the rating and that the time intervals or close enough to keep the overall temperature down on the tube. Exceeding Plate dissipation causes excessive secondary emissions and internal grid leakage. It is also the biggest cause of vacuum loss because of leaking seals at the anode connection. Poor vacuum causes more grid leakage and emission loss due to corroded heaters. Over temp on a tube is not good even for a short period of time. In a class B circuit with no input or output the plate dissipation must be below the limit. If the input is varying as it is with SSB or audio then the tube will pass through an area of much higher dissipation. This area is generally (but not always) somewhere near the 50% mark of peak drive and output. This means, the tube could actually be hot with just a carrier and, then cool down when the input is modulated with a tone. As I recall 811s do not (or just barely) show color at 65 watts dissipation. This would be static 2000V and 32 ma or 1500 volts and 43ma. Good practice would be to set bias some what below current for 65 watts dissipation. As input carrier is introduced a output carrier will also be created. It should be a linear progression until top end is met. During this progression the tube will go through various levels of efficiency and plate dissipation. Some of the places will be very close to or exceeding the limit of 65 watts. A point of best operation would be where the output is 25 % or less of the peak output POWER level (OR 50% of the RF output VOLTAGE) and the plate dissipation (input power - output power) is less that 65 watts per 811A. Good Luck to all John WA5BXO
RE: [AMRadio] AM Usage with Linear AMPS
I don't know, I never had any linear amps. I suppose you can run them as high as you like provided: The plate dissipation is not exceeded (ccs45 watts, icas 65 watts per tube), The modulation peaks don't get cut off, The power supply can take the constant current and peaks. The actual class of service might come into play, AB1, AB2, or class B. >From what I have heard, some modern amps have really wimpy power supplies. Looking at the tube info in the RCA book, I don't have any idea how to figure out the maximum pep and AM carrier ratings. In class B audio, you can push a pair of 811A's to 340 watts. Would that be like 340 watts pep? 1/4 carrier power would be 85 watts of carrier for 2 tubes at 1500 volts. If you go by the AB2 info, at 1500 volts you get 160 watts pep for two tubes. That's 40 watts of carrier, 80 watts out for 4 tubes, in ICAS service per RCA. Now, if you don't assume 4 times the carrier power under modulation, you can up the carrier power I guess, or even limit the peaks. Say you figure on only 2 times the carrier, you could maybe get a lot more carrier output. 160 watts with 2 times the carrier modulation, 4 tubes at 1500 volts. Brett N2DTS
Re: [AMRadio] AM Usage with Linear AMPS
Brian, What he is saying is: you need to have the 811A tuned up at 200 watts output on cw or pep for a 50 watt carrier out. (pep is 4 times carrier) When you tune up you tune it for max output at the 200 watt level with full drive. At that tune setting the tube will be around 60% efficient. Normal ssb or cw operation tune-up. input power will be 333 watts. The tube will be dissipating 133 watts in heat at full carrier. You then reduce the drive until you have 50 watts out (1/4 the carrier of full output). You can not retune at this point or it will not handle the peak envelope power of 4 times carrier. At 50 watts out the efficiency drops to around 30%. So that means to get the 50 watts out the tube has to be running around 150 watts input. 150 watts minus the 50 watts output leaves 100 watts to dissipate in heat in the plate as long as the carrier is on. It doesn't get any better either. With modulation the dissipation does not decrease even though the efficiency increases at the peak power levels. The carrier power is still there 100% of the time at 30% efficiency. The audio is in the form of separate side bands that is additional power that the tube has to handle. I guarantee you that an 811A will run with a red plate under these conditions. If it is not red then it is not tuned up properly for this mode of operation at the 50 watt carrier out level. 73 Gary K4FMX Brian Carling wrote: On 22 Nov 2004 at 20:23, [EMAIL PROTECTED] wrote: Going to shorten it's life considerably. Theoretically maybe. Have you tried it. How can you know for sure? Theory says a bumble bee can't fly. My 811A tubes never burned up. Where did you get your 30% number from? Who transmits their AM with carrier only!? I can't see how a 50 watt carrier input will cause an 811A to DISSIPATE 100 watts! Where are you getting the additional 50? To properly adjust a linear amp for AM it is necessary to tune the thing up for the peak power level, i.e., 200 watts for a 50W carrier. The linear will be about 60% efficient at this output level. Then WITHOUT CHANGING THE TUNING adjust the output from the AM exciter to provide for 50W out of the linear with no modulation. The problem here is that the linear will now only be running about 30% efficiency under carrier-only conditions and the 811 would be dissipating something like 100+ watts. The 811A, of course, is only rated at 65 watts. Dennis D. W7QHO Glendale, CA __ AMRadio mailing list Home: http://mailman.qth.net/mailman/listinfo/amradio Help: http://mailman.qth.net/mmfaq.html Post: mailto:AMRadio@mailman.qth.net
Re: [AMRadio] AM Usage with Linear AMPS
On 22 Nov 2004 at 20:23, [EMAIL PROTECTED] wrote: > Going to shorten it's life considerably. Theoretically maybe. Have you tried it. How can you know for sure? Theory says a bumble bee can't fly. My 811A tubes never burned up. Where did you get your 30% number from? Who transmits their AM with carrier only!? I can't see how a 50 watt carrier input will cause an 811A to DISSIPATE 100 watts! Where are you getting the additional 50? > To properly adjust a linear amp for AM it is necessary to tune the thing up > for the peak power > level, i.e., 200 watts for a 50W carrier. The linear will be about 60% > efficient at this output level. > Then WITHOUT CHANGING THE TUNING adjust the output from the AM exciter to > provide for > 50W out of the linear with no modulation. The problem here is that the linear > will now only be > running about 30% efficiency under carrier-only conditions and the 811 would > be dissipating > something like 100+ watts. The 811A, of course, is only rated at 65 watts. > > Dennis D. W7QHO > Glendale, CA
Re: [AMRadio] AM Usage with Linear AMPS
On 22 Nov 2004 at 20:23, [EMAIL PROTECTED] wrote: > Going to shorten it's life considerably. Theoretically maybe. Have you tried it. How can you know for sure? Theory says a bumble bee can't fly. My 811A tubes never burned up. > To properly adjust a linear amp for AM it is necessary to tune the thing up > for the peak power > level, i.e., 200 watts for a 50W carrier. The linear will be about 60% > efficient at this output level. > Then WITHOUT CHANGING THE TUNING adjust the output from the AM exciter to > provide for > 50W out of the linear with no modulation. The problem here is that the linear > will now only be > running about 30% efficiency under carrier-only conditions and the 811 would > be dissipating > something like 100+ watts. The 811A, of course, is only rated at 65 watts. > > Dennis D. W7QHO > Glendale, CA
RE: [AMRadio] AM Usage with Linear AMPS
On 22 Nov 2004 at 8:29, Brett gazdzinski wrote: > Hu, > How many 811a's in that amp? > > If 4, then I think the 811a has 65 watts of plate dissipation, 4x65=260. > Cut 260 watts in half for 130 watts of carrier output, but I doubt I > would > run them > that hard. The power supply likely wont take that much abuse, its > designed > for > ssb service, very low duty cycle! > > Figure maybe 100 watts out, but watch things closely. 25 watts out per 811A with 100 watts p.e.p. - heck you can do better than that woth sweep tubes. I am certain you can run 811As at double that power in AM linear service with impunity. 50 watts AM output is surely not going to hurt a good ole 811A, LOL! I have done similar with several 4X 811A linear amps and they didn't even glow red, let alone pop a tube! With forced air cooling they should be fine. Am I crazy?
RE: [AMRadio] AM Usage with Linear AMPS
Hu, How many 811a's in that amp? If 4, then I think the 811a has 65 watts of plate dissipation, 4x65=260. Cut 260 watts in half for 130 watts of carrier output, but I doubt I would run them that hard. The power supply likely wont take that much abuse, its designed for ssb service, very low duty cycle! Figure maybe 100 watts out, but watch things closely. You could likely pop in 572b tubes, 160 watts of plate dissipation, for a total of 640 watts of dissipation, 320 watts carrier output, but the amp would never support that, the power supply will just laugh at you. Four 811a's in plate modulated service at 1500 volts would give you 500 watts of carrier out all day long. Two 811a's in push pull class C do 250 to 300 watts of carrier.. Going from 25 to 100 watts is a help, but be careful with the amp Brett N2DTS -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Ralph Daniels Sent: Monday, November 22, 2004 7:55 AM To: amradio@mailman.qth.net Subject: [AMRadio] AM Usage with Linear AMPS Hi all, I feel this subject must have been covered many times but I just can't find it. Specifically, I have a Heathkit HX-10 Marauder driving an Ameritron AL-811H on CW and SSB and would also like to try it on AM. The driving power on AM is 25 watts. Is this a correct use of the amplifuer and if so what are some operationa guidelines as regards i/p and o/p power, duty cycle, cooling etc. Thanks in advance, Ralph Daniels, N1SK __ AMRadio mailing list Home: http://mailman.qth.net/mailman/listinfo/amradio Help: http://mailman.qth.net/mmfaq.html Post: mailto:AMRadio@mailman.qth.net
RE: [AMRadio] AM Usage with Linear AMPS
Ralph Rote: > ... what are some operationa guidelines as regards i/p and o/p power, duty cycle, cooling etc. Ralph, ultimately what you're looking for is to run the amp at 1/4 the maximum CW output of the amp. In other words, if the amp runs 800 W output on CW you want to drive it to only 200 W output max. This allows for proper headroom for modulation. Otherwise Eddy's guidelines are correct. Ed, VA3ES
Re: [AMRadio] AM Usage with Linear AMPS
Ralph, A good rule of thumb to follow is simply this: the maximum carrier output you're going to safely get out of your separate linear amplifier is limited to HALF of the plate dissipation of your linear's tube(s)... Example: I sometimes drive my HB 2 x 813 as a linear for AM. Each tube has a plate dissipation of 125-watts. HALF of that is 62.5-watts, so with 2 tubes, it'll be 125-watts carrier output MAXIMUM. I adjust my drive to the linear, watching the output power meter, until 125-watts is achieved. I might "tweak" the plate tuning capacitor after this is done. It takes some 10-12 watts of AM to get 125-watts out of the 813s. When speaking into the mic, I always watch the trapezoidal pattern on my SB-610 'scope, & make sure I have enough audio. Hope this helps! ~73~ Eddy VE3CUI - VE3XZ - Original Message - From: "Ralph Daniels" <[EMAIL PROTECTED]> To: Sent: Monday, November 22, 2004 7:54 AM Subject: [AMRadio] AM Usage with Linear AMPS > Hi all, > > I feel this subject must have been covered many times but I just can't find it. > > Specifically, I have a Heathkit HX-10 Marauder driving an Ameritron AL-811H > on CW and SSB and would also like to try it on AM. The driving power on AM > is 25 watts. > > Is this a correct use of the amplifuer and if so what are some operationa > guidelines as regards i/p and o/p power, duty cycle, cooling etc. > > Thanks in advance, > > Ralph Daniels, N1SK > > > > __ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net >
