RE: [AMRadio] re: looking for linear amplifier
At 04:53 PM 12/20/2003, you wrote: Actually if you want to build a high power high level homebrew transmitter, there is no need to spend megabucks to purchase a custom built mod transformer. There are plenty of tube type broadcast transmitters sitting around all over the country that have been removed from service. These can be bought for very little, and often are offered for free if you are willing to remove the entire transmitter from the premises. Abandoned AM BC transmitters have become a presently available industrial surplus item. Some hams prefer to make a few modifications and convert the BC transmitter directly to ham use, but they contain a wealth of parts for someone who prefers to homebrew from scratch. This involves completely redesigning the layout using the same parts, and most likely building a new rack or enclosure, which may or may not be constructed from materials salvaged from the old, highly oversized and overweight broadcast transmitter cabinet. The challenge is to find out about a discarded BC transmitter before it is hauled to the landfill. Don K4KYV So whats the secret to finding AM broadcast transmitters?
Re: [AMRadio] AM from what I have in the junk box
My PDM-AM rig uses a single 833A as the modulator... -Larry/NE1S Geoff/W5OMR wrote: > > Subject: [AMRadio] AM from what I have in the junk box > > > Anyone have any nice schematics to construct a AM transmitter from some > > 4-125As or 4-65As that I have available?? Also have a new 833a that > > could be used for a modulator. > > you need more than one tube for a modulator... > > ...usually > > ___ > AMRadio mailing list > AMRadio@mailman.qth.net > http://mailman.qth.net/mailman/listinfo/amradio
RE: [AMRadio] re: looking for linear amplifier
> ... If one needs an 800 watt amplifier to run > 100 watts AM, then how does a Viking with 3 > small 6146s run 125 watts AM? What do you mean by an 800-watt amplifier? At a minimum, you need a linear amplifier with only 400 watts peak output capability to run 100 watts steady carrier AM @ 100% modulation. Using linear amplifiers to amplify low-level-modulated signals is a viable mode of operation for radio services that transmit on an intermittent basis at relatively low power levels (as amateur radio does). However, in radio services such as broadcasting where the transmitter is on the air continuously (at high power levels), the electric power wastage becomes a significant expense factor. And the roughly 4X increase in power supplies and tubes required presents an unjustifiable capital expense, even for amateur stations. The result is the almost universal adoption of high-level modulated transmitters by both commercial and amateur operators. Actually, linear amplifiers preceeded high level plate modulators for high power AM broadcast transmitters. Originally, the class-B amplifier was used in rf linear service. It wasn't until the late 1920's that someone figured out that class-B could be used to amplify AUDIO signals as well, by simply making the amplifier push-pull so that both sides of the audio waveform would be produced. In a single-ended class-B linear, the missiing half of the rf cycle is generated by the flywheel effect of the rf tank circuit. Before the advent of the class-B audio amplifier, plate modulated transmitters depended on class-A audio amplifiers for modulators, usually in the "Heising modulation" configuration. These transmitters were even less efficient than class-B rf linears, because the class A modulator ran typically at less than 20% efficency. The total a.c. power input vs rf power output of these transmitters was very very low, substantially less than that of a class-B linear or a low-level grid modulated final. Once suitable audio driver and output (modulation) transformers became available in the early 1930's, high level class-B modulation systems became popular because less expensive tubes having lower plate dissipation ratings could be used. Like today, tubes sold at a premium during the depression era. However, the total overall efficiency of a a high level class-B plate modulated amplifier is not much different form that of a low level (grid modulated or linear) amplifier. Losses in low level modulated transmitters lie mainly in the power dissipated by the final amplifier tube. In the high level plate modulated rig, there is plate dissipation loss in the class-B audio amplifier (remember it is also as linear amplifier) plus modulator tube filament power, plus the power consumed by the class-B audio driver stage. Continental Electronics, a long time manufacturer of broadcast transmitters, never offered a plated modulated product. Their advertisements always pointed out that from a BC station's vantage point, low level and high level modulated (tube type) transmitters are about equally economical to operate in terms of the electric bill for running the transmitter. The emergence of the requirement of linear amplification for SSB over the past half century has resulted in the creation of relatively cheap linear amplifiers for amateur radio use - so much so, in fact, that the economics have now swung back in favor of low-level modulation, or at least placed it on par with high-level methods. Very true. And like AM, a properly operating SSB transmitter operates at much lower average power than what it generates on occasional voice peaks. That means that most of the time, the SSB linear is just as inefficient as the AM linear. The main difference is that with SSB you don't have the constant power dissipated in the plates of tubes as heat as a result of delivering a steady carrier. Price a modulation transformer from Peter Dahl, or look at the nearly $4000 tag on the resurrected Globe King 500D. That Ranger driving a funky old Heath SB-220 begins to look pretty good. Actually if you want to build a high power high level homebrew transmitter, there is no need to spend megabucks to purchase a custom built mod transformer. There are plenty of tube type broadcast transmitters sitting around all over the country that have been removed from service. These can be bought for very little, and often are offered for free if you are willing to remove the entire transmitter from the premises. Abandoned AM BC transmitters have become a presently available industrial surplus item. Some hams prefer to make a few modifications and convert the BC transmitter directly to ham use, but they contain a wealth of parts for someone who prefers to homebrew from scratch. This involves completely redesigning the layout using the same parts, and most likely building a new rack or enclosure, which may or may
Re: [AMRadio] Swampland in Arizona
Excuse this "spam" but I have some "Swampland in Arizona" that is available. It is listed on Eham Classifieds under "Ham Homes". http://www.eham.net/classifieds/detail/117028 6.8 acres on a hill with gorgeous scenery, beverage antennas and grandfathered towers. 73 & Merry Xmas to all, DE Damon, W7MD Tucson, AZ - Original Message - From: "RoadKing" <[EMAIL PROTECTED]> To: Sent: Saturday, December 20, 2003 10:49 AM Subject: [AMRadio] Swampland in Arizona > Hey Jim! > > As the "Owner" of some of the most exquisite Swampland in Arizona, I was > very happy to see that you TOO have the deed/ownership to some property in > what is certain to become some of the most sought after "Retirement" > hideaways in the entire state. My property was acquired one tract at a > time from some "Dream" Seekers also offering up similar products. >
[AMRadio] re: looking for linear amplifier
Paul, WA3GFZ, wrote: > ... If one needs an 800 watt amplifier to run > 100 watts AM, then how does a Viking with 3 > small 6146s run 125 watts AM? It's due to the difference in efficiency between a non-linear, plate-modulated, Class-C amplifier and a linear, Class-AB2 amplifier. A Class-C amplifier can have up to 80% efficiency, so making a 125-watt output would only require 156 watts of plate power input and the final tubes would dissipate 31 watts. Things are not that neat, so a typical 125-watt final runs a pair of 25-watt-plate-dissipation 6146's. (The Valiant is actually capable of 150+ watts output). However, Class-C amplifiers are NOT LINEAR. Driving one with a modulated RF signal results in a severely distorted output signal that is useless for communications. The extreme nonlinearity of a Class-C amplifier is actually the reason it is able to achieve its high efficiency. The reason the modulation is not distorted in a modulated Class-C amplifier is that it is applied in series with the plate supply and actually varies the gain of the Class-C stage in a linear manner without relying on the amplification of the stage itself. Amplifying an RF signal already modulated by the driver (in the present case, the Ranger) requires a linear amplifier. Linear amplifiers have low efficiencies at low signal levels and only achieve reasonable efficiency on signal peaks. Unfortunately, for AM, the carrier level must be held at 1/4 the peak output power, so it is always in the low-efficiency part of the linear-amplifier characteristic. If the carrier amplitude is raised so that it is in the high-efficiency part of the linear-amplifier characteristic, positive modulation peaks will cause the amplifier to saturate and extreme distortion will result. Using linear amplifiers to amplify low-level-modulated signals is a viable mode of operation for radio services that transmit on an intermittent basis at relatively low power levels (as amateur radio does). However, in radio services such as broadcasting where the transmitter is on the air continuously (at high power levels), the electric power wastage becomes a significant expense factor. And the roughly 4X increase in power supplies and tubes required presents an unjustifiable capital expense, even for amateur stations. The result is the almost universal adoption of high-level modulated transmitters by both commercial and amateur operators. The emergence of the requirement of linear amplification for SSB over the past half century has resulted in the creation of relatively cheap linear amplifiers for amateur radio use - so much so, in fact, that the economics have now swung back in favor of low-level modulation, or at least placed it on par with high-level methods. Price a modulation transformer from Peter Dahl, or look at the nearly $4000 tag on the resurrected Globe King 500D. That Ranger driving a funky old Heath SB-220 begins to look pretty good. Jim Bromley, K7JEB Glendale, AZ
Re: [AMRadio] Swampland in Arizona
Glad I have my hip waders on :) -- Original Message --- From: RoadKing <[EMAIL PROTECTED]> To: amradio@mailman.qth.net Sent: Sat, 20 Dec 2003 11:49:43 -0600 Subject: [AMRadio] Swampland in Arizona > Hey Jim! > > As the "Owner" of some of the most exquisite Swampland in Arizona, I > was very happy to see that you TOO have the deed/ownership to some > property in what is certain to become some of the most sought after > "Retirement" hideaways in the entire state. My property was > acquired one tract at a time from some "Dream" Seekers also offering > up similar products. > > I find the Conduction cooled Heat sink approach to cooling the shack > a much preferred avenue rather than total Hot Air Expulsion. I at > present am seeking a patent on a very unique (H.A.E.) Valve. It was > designed here at the 'River House' and has been going thru R & D > with what is considered by many to be totally successful. Jim, I > hate to offer up a suggestion but perhaps thru some '3rd' party we > can combine our collective properties and build a true mecca for > developing future new ideas worthy of acceptance by those perhaps > less astute in the complicated world of new design. I've come up > with a simple formula for working with some fairly complicated > mathematics involved in tracing the first frequency of Audio through > all the many, tubes,capacitors, resistors that comprise an "AM" emission. > > GVC + GM x GSA + SMT + GFT = SSAMS > > This simple Formula works for me and many others that I hear out > there on the bands. Thanks Jim for reminding me of this simple formula. > > 73, > Tony/W5OD > River House Radio > Boling, TX > > ___ > AMRadio mailing list > AMRadio@mailman.qth.net > http://mailman.qth.net/mailman/listinfo/amradio --- End of Original Message ---
RE: [AMRadio] Swampland in Arizona
Hey guys, I got a novel idea. Lets fire up on 7290 AM, and get off the internet. Going to turn on the filaments momentarily... Jim -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of John Coleman, ARS WA5BXO Sent: Saturday, December 20, 2003 12:26 PM To: amradio@mailman.qth.net Subject: RE: [AMRadio] Swampland in Arizona I don't know Geoff, I think the real, universal, and best part, for a loss of better words, might be lost the lengthy, but I'm sure exquisite, explanation. Tony has my vote as the best in this category. BXO -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Geoff Edmonson Sent: Saturday, December 20, 2003 12:12 PM To: amradio@mailman.qth.net Subject: Re: [AMRadio] Swampland in Arizona I imagine Tony wouldn't mind you quoting it, all you wanted. I think a prerequisite, however, would be to have him Explain it, first! ;-) ___ AMRadio mailing list AMRadio@mailman.qth.net http://mailman.qth.net/mailman/listinfo/amradio
RE: [AMRadio] Swampland in Arizona
I don't know Geoff, I think the real, universal, and best part, for a loss of better words, might be lost the lengthy, but I'm sure exquisite, explanation. Tony has my vote as the best in this category. BXO -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Geoff Edmonson Sent: Saturday, December 20, 2003 12:12 PM To: amradio@mailman.qth.net Subject: Re: [AMRadio] Swampland in Arizona I imagine Tony wouldn't mind you quoting it, all you wanted. I think a prerequisite, however, would be to have him Explain it, first! ;-)
Re: [AMRadio] Swampland in Arizona
I spewed my drink all over the monitor when on Saturday 20 December 2003 12:07, John Coleman, ARS WA5BXO said (and I am -not- making this up!):: > May I have the profound pleasure of quoting this some day? > > BXO I imagine Tony wouldn't mind you quoting it, all you wanted. I think a prerequisite, however, would be to have him Explain it, first! ;-) -- 12:10pm up 12:21, 5 users, load average: 0.18, 0.14, 0.15
RE: [AMRadio] Swampland in Arizona
May I have the profound pleasure of quoting this some day? BXO -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of RoadKing Sent: Saturday, December 20, 2003 11:50 AM To: amradio@mailman.qth.net Subject: [AMRadio] Swampland in Arizona Hey Jim! As the "Owner" of some of the most exquisite Swampland in Arizona, I was very happy to see that you TOO have the deed/ownership to some property in what is certain to become some of the most sought after "Retirement" hideaways in the entire state. My property was acquired one tract at a time from some "Dream" Seekers also offering up similar products. I find the Conduction cooled Heat sink approach to cooling the shack a much preferred avenue rather than total Hot Air Expulsion. I at present am seeking a patent on a very unique (H.A.E.) Valve. It was designed here at the 'River House' and has been going thru R & D with what is considered by many to be totally successful. Jim, I hate to offer up a suggestion but perhaps thru some '3rd' party we can combine our collective properties and build a true mecca for developing future new ideas worthy of acceptance by those perhaps less astute in the complicated world of new design. I've come up with a simple formula for working with some fairly complicated mathematics involved in tracing the first frequency of Audio through all the many, tubes,capacitors, resistors that comprise an "AM" emission. GVC + GM x GSA + SMT + GFT = SSAMS This simple Formula works for me and many others that I hear out there on the bands. Thanks Jim for reminding me of this simple formula. 73, Tony/W5OD River House Radio Boling, TX ___ AMRadio mailing list AMRadio@mailman.qth.net http://mailman.qth.net/mailman/listinfo/amradio
Re: [AMRadio] Looking for Linear Amp
Thanks to all for the information. The way everyone explained it makes perfect sense. Besides putting up the better antenna, I think the better way is to get a viking 2 or similar radio and get the 125 watts without having to purchase the linear. 73s and thanks again, Paul From: "John Coleman, ARS WA5BXO" <[EMAIL PROTECTED]> To: Sent: Saturday, December 20, 2003 11:48 AM Subject: RE: [AMRadio] Looking for Linear Amp > The Ranger, Viking, DX100 and the 32V3, etc. rigs are running Class C > finals using plate modulation. They do not have an RF linear amplifier > in them. Being a new comer you may not be familiar with the pros and > cons of linear verses class C. I will try to stir up some interest here > in maybe home brewing a larger rig but first you need to now a little > about what you might build. Rigs such as Yasues, and Kenwoods, and > other more modern SSB type, "Rice Box type" to coin a phrase, including > the ones that have an AM mode, have small linear amplifiers built into > the box. The modulation is done at a very low level (less than a watt) > then the whole envelope (carrier plus sidebands in the case of AM mode) > is amplified by the built in linear amplifiers to a 20 - 150 watt level > depending on the mode and rig. These rigs may use a pair of 6146s for > the linear amp outputs running in class AB1 or AB2. In the case of the > Rangers and others the RF carrier is amplified using non linear class C > circuits. We don't care if the amplifiers have a lot of RF distortion > in the carrier because each stage is tuned with a LC circuit that > removes the distortion and puts the output of each stage back to a pure > sine wave at a single frequency of RF. Prior to tuning, these stages > are rich in harmonic distortion because of the clipping of the current > in the tube's class C biasing. They even tune some of the lower level > stages outputs to the second harmonic so that, for example, the VFO may > run on 1.9 MHZ and the output on 3.8 MHZ. At the last stage of class C > amplification, the signal is tuned and matched to the antenna line. The > carrier that is produce here is modulated by varying the plate supply > voltage to the output stage (6146), with the audio wave form. This > requires a high level audio amplifier (also built in the Ranger box). > This audio amplifier is similar to any PA type amplifier with the > exception that it's output XFMR is not designed to drive speakers but > instead to match the impedance of the Class C final (6146), > Ep/IP=Zmodulated. This is high level modulation. The Class C finals > are good for CW, FM and AM high level modulation because of their high > plate efficiency (70 - 80%). There or efficient because they don't > spend much time between cutoff and saturation. Much like a switch that > doesn't get hot as long as it is all the way on or off. But if you > replace the switch with a normal variable resistor to try to actually > control the level of output power then the resistor will produce a lot > of heat. The power of the heat dissipation in the resistor plus the > delivered output power is equal to the total input power. The linear > amplifiers work similarly as for as efficiency is concerned. This does > not mean that they are not a viable answer to you needs. The class C > rigs of a few hundred watts require a large audio amplifier for the > modulator. For instants, you might use your Ranger in CW mode to drive > a pair of 812s in class C mode at a plate input power of 400 watts. In > class C at this level, these will produce about 300 watts RF output and > dissipate 100 watts in heat. You will need at least 200 watts of audio > to modulate the 400 watt DC to the finals. This could be produce by a > pair of 811As for modulators. You will need a modulation XFMR, filament > XFMRS of finals and modulators. Enough plate voltage supply to power > both modulator and final. You will also need the audio preamp stages > for the modulator unless you plan on extracting the audio for the Ranger > since it is not being used in the Ranger. Remember the Ranger in CW > mode, is their to produce a carrier to drive the 812s and you only need > 10 to 20 watts to do that so the audio circuitry in the Ranger is idle. > I believe it has jumpers on the ACC plug that can be modified for this > purpose. A linear on the other hand uses the AM output of the Ranger > and requires on audio of its own. Simplicity trade off for plate > efficiency. As to which ay is best for you depends, on what's > available, your space, and what you want to learn. > > Good Luck, > John > > > -Original Message- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Paul Sokoloff > Sent: Friday, December 19, 2003 9:30 PM > To: amradio@mailman.qth.net > Subject: Re: [AMRadio] Looking for Linear Amp > > Hello again, > I had no idea I was going to stir up such an interesting discussion. > I > was the person who originally posted thi
[AMRadio] Swampland in Arizona
Hey Jim! As the "Owner" of some of the most exquisite Swampland in Arizona, I was very happy to see that you TOO have the deed/ownership to some property in what is certain to become some of the most sought after "Retirement" hideaways in the entire state. My property was acquired one tract at a time from some "Dream" Seekers also offering up similar products. I find the Conduction cooled Heat sink approach to cooling the shack a much preferred avenue rather than total Hot Air Expulsion. I at present am seeking a patent on a very unique (H.A.E.) Valve. It was designed here at the 'River House' and has been going thru R & D with what is considered by many to be totally successful. Jim, I hate to offer up a suggestion but perhaps thru some '3rd' party we can combine our collective properties and build a true mecca for developing future new ideas worthy of acceptance by those perhaps less astute in the complicated world of new design. I've come up with a simple formula for working with some fairly complicated mathematics involved in tracing the first frequency of Audio through all the many, tubes,capacitors, resistors that comprise an "AM" emission. GVC + GM x GSA + SMT + GFT = SSAMS This simple Formula works for me and many others that I hear out there on the bands. Thanks Jim for reminding me of this simple formula. 73, Tony/W5OD River House Radio Boling, TX
Re: [AMRadio] Looking for Linear Amp
Paul: Others have answered your question about Class C RF amps vs. Class AB linears. You can certainly use your Ranger to drive an amp like an SB220 for fully modulated AM at ~400watts carrier. Enough to make you a 'big gun'. BUT, you'll have to either modify the Ranger to permit reduction of its output to ~10-20 watts (variable screen voltage is one way), or attenuate the output accordingly. I much prefer the former method as it allows much better modulation performance and takes a load off the Ranger final. Using linears for AM like this is purely a convenience approach, as linear amplifiers are plentiful out there at reasonable cost. High level, high power AM transmitters are not. Using a linear is a legitimate way to get on quickly an start enjoying AM with a decent signal. You can 'move up' to big iron later if you like. But you must be very careful about how the exciter (Ranger, etc.) and linear are adjusted and operated. You can quickly blow something up or, worse, operate with a terrible on air signal and not know it, eating up wide chunks of the band causing SSB'ers to curse our lot even more. Before buying an amplifier, I'd suggest an oscilloscope to monitor your signal and become intimate with what's going on. Good luck! 73, g Paul Sokoloff wrote: > > Hello again, > I had no idea I was going to stir up such an interesting discussion. I > was the person who originally posted this. After reading all of the replies > and as a newcommer to this, I have one question. If one needs an 800 watt > amplifier to run 100 watts AM, then how does a Viking with 3 small 6146s run > 125 watts AM? > I have a Johnson Ranger (45 watts with one 6146) which I wish to drive > an amplifier for more output (maybe 125 to 150). Should I just get a viking > 2 or an amplifier? Does anyone have an amp they are interested in selling? > Thanks, > > Paul WA3GFZ
RE: [AMRadio] Looking for Linear Amp
SORRY - Typo and writing Corrections I need a proof reader HIH. There are probably more errors!!! Here it is again. The Ranger, Viking, DX100 and the 32V3, etc. rigs are running Class C finals using plate modulation. They do not have an RF linear amplifier in them. Being a new comer you may not be familiar with the pros and cons of linear verses class C. I will try to stir up some interest here in maybe home brewing a larger rig but first you need to now a little about what you might build. Rigs such as Yasues, and Kenwoods, and other more modern SSB type, "Rice Box type" to coin a phrase, including the ones that have an AM mode, have small linear amplifiers built into the box. The modulation is done at a very low level (less than a watt) then the whole envelope (carrier plus sidebands in the case of AM mode) is amplified by the built in linear amplifiers to a 20 - 150 watt level depending on the mode and rig. These rigs may use a pair of 6146s for the linear amp outputs running in class AB1 or AB2. In the case of the Rangers and others the RF carrier is amplified using non linear class C circuits. We don't care if the amplifiers have a lot of RF distortion in the carrier because each stage is tuned with a LC circuit that removes the distortion and puts the output of each stage back to a pure sine wave at a single frequency of RF. Prior to tuning, these stages are rich in harmonic distortion because of the clipping of the current in the tube's class C biasing. They even tune some of the lower level stages outputs to the second harmonic so that, for example, the VFO may run on 1.9 MHZ and the output on 3.8 MHZ. At the last stage of class C amplification, the signal is tuned and matched to the antenna line. The carrier that is produce here is modulated by varying the plate supply voltage to the output stage (6146), with the audio wave form. This requires a high level audio amplifier (also built in the Ranger box). This audio amplifier is similar to any PA type amplifier with the exception that it's output XFMR is not designed to drive speakers but instead to match the impedance of the Class C final (6146), Ep/IP=Zmodulated. This is high level modulation. The Class C finals are good for CW, FM and AM high level modulation because of their high plate efficiency (70 - 80%). These are efficient because they don't spend much time between cutoff and saturation. Much like a switch that doesn't get hot as long as it is all the way on or off. But if you replace the switch with a normal variable resistor to try to actually control the level of output power then the resistor will produce a lot of heat. The power of the heat dissipation in the resistor plus the delivered output power is equal to the total input power. The linear amplifiers work similarly as for as efficiency is concerned. This does not mean that they are not a viable answer to you needs. The class C rigs of a few hundred watts require a large audio amplifier for the modulator. For instants, you might use your Ranger in CW mode to drive a pair of 812s in class C mode at a plate input power of 400 watts. In class C at this level, these will produce about 300 watts RF output and dissipate 100 watts in heat. You will need at least 200 watts of audio to modulate the 400 watt DC to the finals. This could be produce by a pair of 811As for modulators. You will need a modulation XFMR, filament XFMRS of finals and modulators. You also need enough plate voltage supply to power both modulator and final. You will also need the audio preamp stages for the modulator unless you plan on extracting the audio from the Ranger since it is not being used in the Ranger. Remember the Ranger in CW mode, is their to produce a carrier to drive the 812s and you only need 10 to 20 watts to do that so the audio circuitry in the Ranger is idle. I believe it has jumpers on the ACC plug that can be modified for this purpose. A linear on the other hand uses the AM output of the Ranger and requires no audio of its own. Simplicity trade off for plate efficiency. As to which ay is best for you depends, on what's available, your space, and what you want to learn. Good Luck, John -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Paul Sokoloff Sent: Friday, December 19, 2003 9:30 PM To: amradio@mailman.qth.net Subject: Re: [AMRadio] Looking for Linear Amp Hello again, I had no idea I was going to stir up such an interesting discussion. I was the person who originally posted this. After reading all of the replies and as a newcommer to this, I have one question. If one needs an 800 watt amplifier to run 100 watts AM, then how does a Viking with 3 small 6146s run 125 watts AM? I have a Johnson Ranger (45 watts with one 6146) which I wish to drive an amplifier for more output (maybe 125 to 150). Should I just get a viking 2 or an amplifier? Does anyone have an amp they are interested in selling? Thanks,
RE: [AMRadio] Looking for Linear Amp
The Ranger, Viking, DX100 and the 32V3, etc. rigs are running Class C finals using plate modulation. They do not have an RF linear amplifier in them. Being a new comer you may not be familiar with the pros and cons of linear verses class C. I will try to stir up some interest here in maybe home brewing a larger rig but first you need to now a little about what you might build. Rigs such as Yasues, and Kenwoods, and other more modern SSB type, "Rice Box type" to coin a phrase, including the ones that have an AM mode, have small linear amplifiers built into the box. The modulation is done at a very low level (less than a watt) then the whole envelope (carrier plus sidebands in the case of AM mode) is amplified by the built in linear amplifiers to a 20 - 150 watt level depending on the mode and rig. These rigs may use a pair of 6146s for the linear amp outputs running in class AB1 or AB2. In the case of the Rangers and others the RF carrier is amplified using non linear class C circuits. We don't care if the amplifiers have a lot of RF distortion in the carrier because each stage is tuned with a LC circuit that removes the distortion and puts the output of each stage back to a pure sine wave at a single frequency of RF. Prior to tuning, these stages are rich in harmonic distortion because of the clipping of the current in the tube's class C biasing. They even tune some of the lower level stages outputs to the second harmonic so that, for example, the VFO may run on 1.9 MHZ and the output on 3.8 MHZ. At the last stage of class C amplification, the signal is tuned and matched to the antenna line. The carrier that is produce here is modulated by varying the plate supply voltage to the output stage (6146), with the audio wave form. This requires a high level audio amplifier (also built in the Ranger box). This audio amplifier is similar to any PA type amplifier with the exception that it's output XFMR is not designed to drive speakers but instead to match the impedance of the Class C final (6146), Ep/IP=Zmodulated. This is high level modulation. The Class C finals are good for CW, FM and AM high level modulation because of their high plate efficiency (70 - 80%). There or efficient because they don't spend much time between cutoff and saturation. Much like a switch that doesn't get hot as long as it is all the way on or off. But if you replace the switch with a normal variable resistor to try to actually control the level of output power then the resistor will produce a lot of heat. The power of the heat dissipation in the resistor plus the delivered output power is equal to the total input power. The linear amplifiers work similarly as for as efficiency is concerned. This does not mean that they are not a viable answer to you needs. The class C rigs of a few hundred watts require a large audio amplifier for the modulator. For instants, you might use your Ranger in CW mode to drive a pair of 812s in class C mode at a plate input power of 400 watts. In class C at this level, these will produce about 300 watts RF output and dissipate 100 watts in heat. You will need at least 200 watts of audio to modulate the 400 watt DC to the finals. This could be produce by a pair of 811As for modulators. You will need a modulation XFMR, filament XFMRS of finals and modulators. Enough plate voltage supply to power both modulator and final. You will also need the audio preamp stages for the modulator unless you plan on extracting the audio for the Ranger since it is not being used in the Ranger. Remember the Ranger in CW mode, is their to produce a carrier to drive the 812s and you only need 10 to 20 watts to do that so the audio circuitry in the Ranger is idle. I believe it has jumpers on the ACC plug that can be modified for this purpose. A linear on the other hand uses the AM output of the Ranger and requires on audio of its own. Simplicity trade off for plate efficiency. As to which ay is best for you depends, on what's available, your space, and what you want to learn. Good Luck, John -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Paul Sokoloff Sent: Friday, December 19, 2003 9:30 PM To: amradio@mailman.qth.net Subject: Re: [AMRadio] Looking for Linear Amp Hello again, I had no idea I was going to stir up such an interesting discussion. I was the person who originally posted this. After reading all of the replies and as a newcommer to this, I have one question. If one needs an 800 watt amplifier to run 100 watts AM, then how does a Viking with 3 small 6146s run 125 watts AM? I have a Johnson Ranger (45 watts with one 6146) which I wish to drive an amplifier for more output (maybe 125 to 150). Should I just get a viking 2 or an amplifier? Does anyone have an amp they are interested in selling? Thanks, Paul WA3GFZ ___ AMRadio mailing list AMRadio@mailman.qth.net http://mailman.qth.net/ma
RE: [AMRadio] Looking for Linear Amp
Paul, Linear AM as the others have described is not very efficient, but it is often convenient. For me, especially in the winter, it is efficient. Instead of heating the shack with a 1500 watt resistance heater, I can talk on the radio, and heat my shack at the same time with my linear. That is efficient! With a little sophistication I could use the resistance heater, and with a relay switching technique turn off the resistance heater whenever I am transmitting. That way I won't overload my single 115vac 15a outlet in the ham shack. Your question about the Ranger is a good one. Just remember that the 6146 in the RF circuit is operating class C where the efficiency can be more than twice that of linear running class AB, or B. Then the plate modulator is varying the 6146 B+ at an audio rate. When the crest of the modulation reaches 100% positive modulation, the 6146 B+ is doubled, and the current therefore doubles. This results in the peak power to be 4X the carrier value. Another rule of thumb like what Patrick stated is that a Class C plate modulated 6146 has a PEP output comparable to a single 811 in Class B linear mode. So an Ameritron linear with 3 811's running AM linear at the limits of the tubes is comparable to a Johnson valiant with 3 6146's in the final RF amplifier. There is one big difference though. The 6146's won't be running red, but the 811's will be. That is why several others recommend that with linears we throttle back some to increase tube longevity. With this de-rating to be easier on the linear, you could now compare the class C Plate modulated 6146 to a linear amp using a single 813. I run AM with a linear amplifier. I use a Gonset GSB-201 linear which has four type 572B tubes in parallel. This gives me a combined 640 watts of plate dissipation. With 10 (carrier) watts drive from my Central electronics 20A (modified for QRO), I get 200 watts carrier from the Gonset, with headroom to modulate upwards to about 125%. The 572b's only show a little color, so I am not too worried. I do however produce a lot of heat, and this can become unbearable in the summertime (no AC in the garage shack). Sigh. I wonder if one could use a conduction cooled RF amplifier tube attached to a thermoelectric plate with the intent to cool a heat sink. Blow air past the heat sink, and now the linear cools the shack! If you believe that, I got some swampland in Arizona for sale... Regards, Jim -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of RJ Mattson Sent: Friday, December 19, 2003 11:18 PM To: amradio@mailman.qth.net Subject: Re: [AMRadio] Looking for Linear Amp Paul, I believe, increasing your power from a 45 watt Ranger to 180 watts, is just one "S" unit on most receivers. Put your money into a good antenna. bob...w2ami - Original Message - From: "Paul Sokoloff" <[EMAIL PROTECTED]> To: Sent: Friday, December 19, 2003 10:30 PM Subject: Re: [AMRadio] Looking for Linear Amp > Hello again, > I had no idea I was going to stir up such an interesting discussion. I > was the person who originally posted this. After reading all of the replies > and as a newcommer to this, I have one question. If one needs an 800 watt > amplifier to run 100 watts AM, then how does a Viking with 3 small 6146s run > 125 watts AM? > I have a Johnson Ranger (45 watts with one 6146) which I wish to drive > an amplifier for more output (maybe 125 to 150). Should I just get a viking > 2 or an amplifier? Does anyone have an amp they are interested in selling? > Thanks, > > Paul WA3GFZ > > ___ > AMRadio mailing list > AMRadio@mailman.qth.net > http://mailman.qth.net/mailman/listinfo/amradio > ___ AMRadio mailing list AMRadio@mailman.qth.net http://mailman.qth.net/mailman/listinfo/amradio
Re: [AMRadio] Looking for Linear Amp
Paul, I believe, increasing your power from a 45 watt Ranger to 180 watts, is just one "S" unit on most receivers. Put your money into a good antenna. bob...w2ami - Original Message - From: "Paul Sokoloff" <[EMAIL PROTECTED]> To: Sent: Friday, December 19, 2003 10:30 PM Subject: Re: [AMRadio] Looking for Linear Amp > Hello again, > I had no idea I was going to stir up such an interesting discussion. I > was the person who originally posted this. After reading all of the replies > and as a newcommer to this, I have one question. If one needs an 800 watt > amplifier to run 100 watts AM, then how does a Viking with 3 small 6146s run > 125 watts AM? > I have a Johnson Ranger (45 watts with one 6146) which I wish to drive > an amplifier for more output (maybe 125 to 150). Should I just get a viking > 2 or an amplifier? Does anyone have an amp they are interested in selling? > Thanks, > > Paul WA3GFZ > > ___ > AMRadio mailing list > AMRadio@mailman.qth.net > http://mailman.qth.net/mailman/listinfo/amradio >
