[AMRadio] Modulator feedback
I've posed a couple of questions on some other lists and received some good advice, but I am still in need of more. My BC-610-E has a bad feedback or "talk back" problem. I've placed a capacitor across the overload relay (RY-5) and that did eliminate a little of the talk back. However, with much audio gain at all, not nearly enough to attain 100% modulation, I get feedback. Not just talk back, but feedback. I have to assume it's coming from the modulation transformer. The modulator bias is set for 40 ma as specifications state. The bolts on the modulation transformer are all tight. What am I over looking here? I'm using a BC-614-E speech amplifier with a D-104 non amplified mic. I did a few modifications to the dynamic input circuitry of the BC-614 to better match the D-104, but that is the only modification in either the speech amp or the BC-610-E. Rick/K5IZ
RE: [AMRadio] Amplifier to use with my DX-60
I still say, forget the linear, and use less money to build a plate modulator for the DX60. It will work better, sound better, cost less, and heat the shack up less. As I recall the DX 60 has a 6146 in the final for class C CW and puts out about 40-50 watts of carrier if it were plate modulated it would do at least 200 watts PEP and sound great. There is a number of different ways to do the modulator. A lot of guys just find and old PA and a transformer to match to the final. Some build the modulator output stages only, input XFMR tubes and modulation XFMR. Then they drive it with a small microphone amp. That's more stuff to set around on the desk but it works. There are a lot of self contained 25 and 50 watt modulator circuits around and probably a lot of complete one piece store bought modulators as well. As I recall, EICO had a pretty nice one that was to go with the EICO model 720 but it was used on many different rigs as well as being used as a driver for big modulators. A buddy of mine had an ECIO 720 and built a nice home brewed modulator for it using 1625s in AB1. It sounded real good. I built one similar to it with less power output for my Knight Kit T60. The T60 had the same control carrier AM that the DX60 does. What a difference it made when it was plate modulated. Very little modification is necessary in the DX60 to accommodate the external modulator. John, WA5BXO
Re: [AMRadio] Amplifier to use with my DX-60
From: "kenw2dtc" <[EMAIL PROTECTED]> Don says: "So you could run maximum 1500 watts DC input to those tubes, with 500 watts carrier output, and 1000 watts dissipated by the tubes" ***I need a little help with the math here Don. You are suggesting that with a class B linear in AM mode, one can get 2000 watts PEP with 1500 watts input ? Assuming 100% positive peak modulation, yes. ___ This message was typed using the DVORAK keyboard layout. Try it - you'll like it. http://www.mwbrooks.com/dvorak/ http://gigliwood.com/abcd/
RE: [AMRadio] Amplifier to use with my DX-60
Thanks so much for taking the time to remind me about all this stuff!!! When I was 25 I worked on a Gates 50B that was as old as I was. I mostly just monitored voltages and looked for trouble. I was facsinated back then as I find myself being now while I foray into the world of AM again. I spent too much time in Broadcast as a studio tech. Cheers, Alan VY2WU Quoting Donald Chester <[EMAIL PROTECTED]>: > > > > >From: Alan Beck <[EMAIL PROTECTED]> > > >I would like to use a cheap am with my DX-60. > > > >An SB-200-230 seems to be a Class B amp. There for it only conducts on the > >positive going cycle. I don't mean to sound silly, but someone told me I > >could run this in SSB Mode using AM input from my DX-60, I run 100 Watts > >carrier for 400 Watts peak, now that makes sense. > > > >What does not make sense is how do I get the other side of the wave > >form The Tank??? I guess the tank. > > > > The linear will work on AM as long as you don't exceed the peak power output > > rating. Exceeding the peak output rating will cause the signal to flat-top, > > distort and splatter. > > Another thing to watch for is the plate dissipation of the tubes. If I > recall correctly, the SB-200 series uses a pair of 3-500Z tubes in the > final. That means you have 1000 watts of plate dissipation available. > Running AM linear @ 100% modulation will give carrier output efficiency of > about 30%. So you could run maximum 1500 watts DC input to those tubes, > with 500 watts carrier output, and 1000 watts dissipated by the tubes. With > > modulation, the tubes will actually cool down slightly, since the DC input > will not vary, but the amplifier will deliver sideband power in addition to > carrier power output. So some of the input power will be converted to rf in > > the sidebands instead of heat in the tube plates. > > But you also have to be careful with the power supply. AM runs at 100% duty > > cycle, so the power supply in the amplifier may not be rated to run 1500 > watts continuous duty. After a few minutes, the power transformer may > overheat. In that case you will have to run it at reduced power. But be > careful that the plate efficiency does not exceed about 33%. If you run it > at too high plate efficiency, it will not leave you enough headroom to > accomodate the positive peaks, and flat-topping/distortion/splatter will > result. > > Don't worry about the missing half of the rf cycle. It works with AM > exactly the same way as it does with SSB. Since the amplifier is single > ended and not pushpull, the missing half of the rf cycle is filled in by the > > "flywheel effect" of the rf tank circuit. > > In summary, with class-B linear AM operation, the final will run about 33% > carrier efficiency. The peak efficiency on modulation peaks will be about > double that, 67%. Two-thirds of the DC input to the final will be > dissipated as heat in the plates of the tubes under carrier-only, no > modulation conditions. That means the carrier output will be one half the > plate dissipation of the tubes. The peak power output should be about 4 > times the resting carrier output at 100% modulation, if flat-topping is to > be avoided. > > Linear amplifier AM operation dates back to the very earliest days of radio. > > The earliest high power broadcast stations used it. It was used for years > > before anyone figured out how to run audio amplifiers in class-B. Before > then, the only kind of high level plate modulation that was used employed > class A audio amplifiers, usually the "Heising" circuit but sometimes series > > modulation was used. Both those systems ran at lower ovarall efficiency > than linear rf amplification. Therefore, AM linears were used long before > high level plate modulation for high powered AM transmitters. > _ > > This message was typed using the DVORAK keyboard layout. Try it - you'll > like it. > http://www.mwbrooks.com/dvorak/ > http://gigliwood.com/abcd/ > > > __ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb >
Re: [AMRadio] Amplifier to use with my DX-60
The SB-200 uses two 572B's. The SB-220 is the amp that uses two 3-500Z's. Joe W4AAB - Original Message - From: "Donald Chester" <[EMAIL PROTECTED]> To: Sent: Thursday, March 16, 2006 3:48 PM Subject: RE: [AMRadio] Amplifier to use with my DX-60 > > > > >From: Alan Beck <[EMAIL PROTECTED]> > > >I would like to use a cheap am with my DX-60. > > > >An SB-200-230 seems to be a Class B amp. There for it only conducts on the > >positive going cycle. I don't mean to sound silly, but someone told me I > >could run this in SSB Mode using AM input from my DX-60, I run 100 Watts > >carrier for 400 Watts peak, now that makes sense. > > > >What does not make sense is how do I get the other side of the wave > >form The Tank??? I guess the tank. > > > > The linear will work on AM as long as you don't exceed the peak power output > rating. Exceeding the peak output rating will cause the signal to flat-top, > distort and splatter. > > Another thing to watch for is the plate dissipation of the tubes. If I > recall correctly, the SB-200 series uses a pair of 3-500Z tubes in the > final. That means you have 1000 watts of plate dissipation available. > Running AM linear @ 100% modulation will give carrier output efficiency of > about 30%. So you could run maximum 1500 watts DC input to those tubes, > with 500 watts carrier output, and 1000 watts dissipated by the tubes. With > modulation, the tubes will actually cool down slightly, since the DC input > will not vary, but the amplifier will deliver sideband power in addition to > carrier power output. So some of the input power will be converted to rf in > the sidebands instead of heat in the tube plates. > > But you also have to be careful with the power supply. AM runs at 100% duty > cycle, so the power supply in the amplifier may not be rated to run 1500 > watts continuous duty. After a few minutes, the power transformer may > overheat. In that case you will have to run it at reduced power. But be > careful that the plate efficiency does not exceed about 33%. If you run it > at too high plate efficiency, it will not leave you enough headroom to > accomodate the positive peaks, and flat-topping/distortion/splatter will > result. > > Don't worry about the missing half of the rf cycle. It works with AM > exactly the same way as it does with SSB. Since the amplifier is single > ended and not pushpull, the missing half of the rf cycle is filled in by the > "flywheel effect" of the rf tank circuit. > > In summary, with class-B linear AM operation, the final will run about 33% > carrier efficiency. The peak efficiency on modulation peaks will be about > double that, 67%. Two-thirds of the DC input to the final will be > dissipated as heat in the plates of the tubes under carrier-only, no > modulation conditions. That means the carrier output will be one half the > plate dissipation of the tubes. The peak power output should be about 4 > times the resting carrier output at 100% modulation, if flat-topping is to > be avoided. > > Linear amplifier AM operation dates back to the very earliest days of radio. > The earliest high power broadcast stations used it. It was used for years > before anyone figured out how to run audio amplifiers in class-B. Before > then, the only kind of high level plate modulation that was used employed > class A audio amplifiers, usually the "Heising" circuit but sometimes series > modulation was used. Both those systems ran at lower ovarall efficiency > than linear rf amplification. Therefore, AM linears were used long before > high level plate modulation for high powered AM transmitters. > _ > > This message was typed using the DVORAK keyboard layout. Try it - you'll > like it. > http://www.mwbrooks.com/dvorak/ > http://gigliwood.com/abcd/ > > > __ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb >
Re: [AMRadio] Amplifier to use with my DX-60
Jim, I guess my question is really: Can anyone actually demonstrate a real AM linear that can output 500 watts carrier and show 2000 watts PEP into a dummy load with a nice looking audio sine wave on the scope, from the RF pickup, while running 1500 watts DC input ? If so, please send me an email at [EMAIL PROTECTED] The reason I ask is: A. None of my amps has ever been that good and B. Unfortunately, a number of people running AM linears do not have scopes and if you tell them that a pair of whatever tubes can achieve a certain carrier power, they will put the carrier to that level via dipping and peaking the pi-net until their wattmeter reaches the specified power and talk. In my experience, by the time you heavily load the output to achieve the perfect audio sine wave, your tuning controls are quite different than what is was when you peaked everything and the efficiency is no longer as good as what the calculations show. On top of that most male voices have peaks that should have an additional de-rating of output power. So when someone asks about what kind of carrier power a certain pair of tubes can put out in AM linear service, I really like to give a conservative number, not the math numbers. 73, Ken W2DTC __ Ken Barber Middletown, NJ Radio Website: http://w2dtc.com Family Photos: http://kenw2dtc.home.comcast.net __ - Original Message - From: "Jim candela" <[EMAIL PROTECTED]> To: "Discussion of AM Radio" Sent: Thursday, March 16, 2006 7:22 PM Subject: RE: [AMRadio] Amplifier to use with my DX-60 Don, You said: "So you could run maximum 1500 watts DC input to those tubes, with 500 watts carrier output, and 1000 watts dissipated by the tubes". Reply from Jim WD5JKO: What is stated above is correct if the tubes can dissipate 1000 watts of heat (like two 3-500Z's flat out blushing), and the drive is adjusted to about 1/4th that for maximum PEP output. In this case the efficiency is assummed to be about 33%, so 1500 X .333 = 500 watts. The efficiency may vary some, and is usually lower then that, so the 33% assumption is only a first guess. It could be 25%, and that really upsets the situation making the linear more of a heater, and less of a transmitter. One good thing about the 1500 watt PEP output power rule we all complain about is that efficiency doesn't matter as much now. You can legally run a 15 KW PEP input amplifier with 10% efficiency to provide 1500 watts PEP output. It wouldn't make a lot of sense, or be practical, but it's now legal. Back in the 1000 watts DC input days things were a lot different, and the SB-220's input would likely exceed 1000 watts DC before the AM carrier got to 375 like we often do today with these amps. The point here is that for low efficiency linears, or grid modulated amplifiers, we can sometimes run more power today on AM then before the rules changed from 1000 watts DC input to 1500 watts PEP output. Of course this isn't the case with plate modulation where an output PEP at or maybe more than 3KW PEP WAS possible, and completely legal. Regards, Jim WD5JKO -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of kenw2dtc Sent: Thursday, March 16, 2006 4:21 PM To: Discussion of AM Radio Subject: Re: [AMRadio] Amplifier to use with my DX-60 Don says: "So you could run maximum 1500 watts DC input to those tubes, with 500 watts carrier output, and 1000 watts dissipated by the tubes" ***I need a little help with the math here Don. You are suggesting that with a class B linear in AM mode, one can get 2000 watts PEP with 1500 watts input ? 73, Ken W2DTC __ AMRadio mailing list Home: http://mailman.qth.net/mailman/listinfo/amradio Help: http://mailman.qth.net/mmfaq.html Post: mailto:AMRadio@mailman.qth.net AMfone Website: http://www.amfone.net AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb -- No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.1.385 / Virus Database: 268.2.4/283 - Release Date: 3/16/2006 -- No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.1.385 / Virus Database: 268.2.4/283 - Release Date: 3/16/2006 __ AMRadio mailing list Home: http://mailman.qth.net/mailman/listinfo/amradio Help: http://mailman.qth.net/mmfaq.html Post: mailto:AMRadio@mailman.qth.net AMfone Website: http://www.amfone.net AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb
Re: [AMRadio] Amplifier to use with my DX-60
Yes, those numbers are possible in amateur service. When I ran a pair of 3-400s linear, I ran about 800 watts carrier input, I got about 160 watts carrier output, disspipation about 640 watts, 200 % mod, and about 1500 PEP out. (Efficiency gets bad when you set them up that way.) If I turned the audio down to about 100%, I could raise the carrier level and get 350 watts carrier output, carrier input about 1100 watts, PEP about 1500 watts, dissipation about 750 watts. The tubes did get hot that way, though. Bacon, WA3WDR - Original Message - From: "Jim candela" <[EMAIL PROTECTED]> To: "Discussion of AM Radio" Sent: Thursday, March 16, 2006 7:22 PM Subject: RE: [AMRadio] Amplifier to use with my DX-60 > > Don, > >You said: "So you could run maximum 1500 watts DC input to those tubes, > with 500 watts > carrier output, and 1000 watts dissipated by the tubes". > > Reply from Jim WD5JKO: > >What is stated above is correct if the tubes can dissipate 1000 watts of > heat (like two 3-500Z's flat out blushing), and the drive is adjusted to > about 1/4th that for maximum PEP output. In this case the efficiency is > assummed to be about 33%, so 1500 X .333 = 500 watts. The efficiency may > vary some, and is usually lower then that, so the 33% assumption is only a > first guess. It could be 25%, and that really upsets the situation making > the linear more of a heater, and less of a transmitter. > >One good thing about the 1500 watt PEP output power rule we all complain > about is that efficiency doesn't matter as much now. You can legally run a > 15 KW PEP input amplifier with 10% efficiency to provide 1500 watts PEP > output. It wouldn't make a lot of sense, or be practical, but it's now > legal. Back in the 1000 watts DC input days things were a lot different, and > the SB-220's input would likely exceed 1000 watts DC before the AM carrier > got to 375 like we often do today with these amps. The point here is that > for low efficiency linears, or grid modulated amplifiers, we can sometimes > run more power today on AM then before the rules changed from 1000 watts DC > input to 1500 watts PEP output. Of course this isn't the case with plate > modulation where an output PEP at or maybe more than 3KW PEP WAS possible, > and completely legal. > > Regards, > Jim > WD5JKO > > > -Original Message- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] Behalf Of kenw2dtc > Sent: Thursday, March 16, 2006 4:21 PM > To: Discussion of AM Radio > Subject: Re: [AMRadio] Amplifier to use with my DX-60 > > > Don says: > > "So you could run maximum 1500 watts DC input to those tubes, with 500 watts > carrier output, and 1000 watts dissipated by the tubes" > > ***I need a little help with the math here Don. You are suggesting that > with a class B linear in AM mode, one can get 2000 watts PEP with 1500 watts > input ? > > 73, > Ken W2DTC > > ___ ___ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb > -- > No virus found in this incoming message. > Checked by AVG Free Edition. > Version: 7.1.385 / Virus Database: 268.2.4/283 - Release Date: 3/16/2006 > > -- > No virus found in this outgoing message. > Checked by AVG Free Edition. > Version: 7.1.385 / Virus Database: 268.2.4/283 - Release Date: 3/16/2006 > > ___ ___ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb >
RE: [AMRadio] Amplifier to use with my DX-60
Don, You said: "So you could run maximum 1500 watts DC input to those tubes, with 500 watts carrier output, and 1000 watts dissipated by the tubes". Reply from Jim WD5JKO: What is stated above is correct if the tubes can dissipate 1000 watts of heat (like two 3-500Z's flat out blushing), and the drive is adjusted to about 1/4th that for maximum PEP output. In this case the efficiency is assummed to be about 33%, so 1500 X .333 = 500 watts. The efficiency may vary some, and is usually lower then that, so the 33% assumption is only a first guess. It could be 25%, and that really upsets the situation making the linear more of a heater, and less of a transmitter. One good thing about the 1500 watt PEP output power rule we all complain about is that efficiency doesn't matter as much now. You can legally run a 15 KW PEP input amplifier with 10% efficiency to provide 1500 watts PEP output. It wouldn't make a lot of sense, or be practical, but it's now legal. Back in the 1000 watts DC input days things were a lot different, and the SB-220's input would likely exceed 1000 watts DC before the AM carrier got to 375 like we often do today with these amps. The point here is that for low efficiency linears, or grid modulated amplifiers, we can sometimes run more power today on AM then before the rules changed from 1000 watts DC input to 1500 watts PEP output. Of course this isn't the case with plate modulation where an output PEP at or maybe more than 3KW PEP WAS possible, and completely legal. Regards, Jim WD5JKO -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of kenw2dtc Sent: Thursday, March 16, 2006 4:21 PM To: Discussion of AM Radio Subject: Re: [AMRadio] Amplifier to use with my DX-60 Don says: "So you could run maximum 1500 watts DC input to those tubes, with 500 watts carrier output, and 1000 watts dissipated by the tubes" ***I need a little help with the math here Don. You are suggesting that with a class B linear in AM mode, one can get 2000 watts PEP with 1500 watts input ? 73, Ken W2DTC __ AMRadio mailing list Home: http://mailman.qth.net/mailman/listinfo/amradio Help: http://mailman.qth.net/mmfaq.html Post: mailto:AMRadio@mailman.qth.net AMfone Website: http://www.amfone.net AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb -- No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.1.385 / Virus Database: 268.2.4/283 - Release Date: 3/16/2006 -- No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.1.385 / Virus Database: 268.2.4/283 - Release Date: 3/16/2006
Re: [AMRadio] Amplifier to use with my DX-60
YES,in fact he could. 100 watts carrier or 80 watts carrier. The power supply is the limiting factor here. The SB200 with a big fan and an external power supply could actually run 160 watts carrier. The word Max is actually maximum. The wimpy supply holds it to about 80 watts. You might like the smell of hot tar and burned kraft paper! I would stick to 80 watts or there abouts and check the transformer with the " can I hold a finger full on it for 3 full seconds" test.. Mike > If I understand these responses this all boils down to answer Alan's > original question and that is that a SB-200 would be ok with the DX-60 at > the DX-60's max output . Correct? > > Tom K3TVC >An SB-200-230 seems to be a Class B amp. There for it only conducts on the > >positive going cycle. I don't mean to sound silly, but someone told me I > >could run this in SSB Mode using AM input from my DX-60, I run 100 Watts > >carrier for 400 Watts peak, now that makes sense. > >
Re: [AMRadio] Amplifier to use with my DX-60
If I understand these responses this all boils down to answer Alan's original question and that is that a SB-200 would be ok with the DX-60 at the DX-60's max output . Correct? Tom K3TVC - Original Message - From: "Mike Dorworth, K4XM" <[EMAIL PROTECTED]> To: "Discussion of AM Radio" Sent: Thursday, March 16, 2006 5:45 PM Subject: Re: [AMRadio] Amplifier to use with my DX-60 > YUP. The two things are the tubes and the power supply.. One half > dissipation is MAX.. you are using 800 watt tubes so 400Watt carrier is max. > The Thunderbolt has a real power supply, so, sure 300 watts is fine.Since > SSB is 25 to 30 percent average of peaks the manufactures can squeeze in > small supplies for voice or CW service. Ever make you wonder that they might > allow 2500 watts input SSB but only 400 for RTTY. AM and RTTY separates the > Men from the boys.. Mike > - Original Message - > From: "Dale Smith" <[EMAIL PROTECTED]> > To: "Mike Dorworth, K4XM" <[EMAIL PROTECTED]>; "Discussion of AM Radio" > > Sent: Thursday, March 16, 2006 5:43 PM > Subject: Re: [AMRadio] Amplifier to use with my DX-60 > > > > How about a Johnson thunder bolt is 300 watt carrier ok ? I hope so > > cause that is what I have been doing > > The transformer in there is twice as big as my swan mark 1. > > thanks ..de/dale/ka5who > > > > __ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb >
Re: [AMRadio] Amplifier to use with my DX-60
YUP. The two things are the tubes and the power supply.. One half dissipation is MAX.. you are using 800 watt tubes so 400Watt carrier is max. The Thunderbolt has a real power supply, so, sure 300 watts is fine.Since SSB is 25 to 30 percent average of peaks the manufactures can squeeze in small supplies for voice or CW service. Ever make you wonder that they might allow 2500 watts input SSB but only 400 for RTTY. AM and RTTY separates the Men from the boys.. Mike - Original Message - From: "Dale Smith" <[EMAIL PROTECTED]> To: "Mike Dorworth, K4XM" <[EMAIL PROTECTED]>; "Discussion of AM Radio" Sent: Thursday, March 16, 2006 5:43 PM Subject: Re: [AMRadio] Amplifier to use with my DX-60 > How about a Johnson thunder bolt is 300 watt carrier ok ? I hope so > cause that is what I have been doing > The transformer in there is twice as big as my swan mark 1. > thanks ..de/dale/ka5who >
Re: [AMRadio] Amplifier to use with my DX-60
How about a Johnson thunder bolt is 300 watt carrier ok ? I hope so cause that is what I have been doing The transformer in there is twice as big as my swan mark 1. thanks ..de/dale/ka5who
[AMRadio] Re: [Hallicrafters] Free magazines
Saw this somewhere; Bob is putting them to the curb. On March 29, several LARGE stacks of QST, CQ, 73, Ham Radio Horizons, and Ham Radio will be put by the curb for recycle. Many of the Ham Radio magazines are in beautiful yellow binders. If you know of anyone who would like to "save" these, please call me at 908-464-7958. W2EME 65 Hillside Ave. Berkeley Heights, NJ
Re: [AMRadio] Amplifier to use with my DX-60
Don says: "So you could run maximum 1500 watts DC input to those tubes, with 500 watts carrier output, and 1000 watts dissipated by the tubes" ***I need a little help with the math here Don. You are suggesting that with a class B linear in AM mode, one can get 2000 watts PEP with 1500 watts input ? 73, Ken W2DTC
Re: [AMRadio] Amplifier to use with my DX-60
Short answer. The SB200 uses a pair of 572B/T160L rated at 160 watts each. AM Linear output can not be more than one half of total dissipation. The power supplies are usually rated for continous service (AM) at 25 percent of the peak. For SB220 a 400 watt transformer is used for 2000 watts pep input. The SB200 is rated at 1200 watts pep input and would have about a 300 watt transformer. If the supply were strong enough the SB200 could run 160 watts carrier. Best to stick with one half of that..80 watts. For the SB220, L4B, TL922A best to stick with 250 watts carrier, or less. The answer below is exactly correct except for the tubes in the SB200.. The SB230 uses a conduction cooled 8873 with about 300 watts dissipation, 80 watts carrier would probably cook it in short order because of the non-cooling system heat load. 73 Mike - Original Message - From: "Donald Chester" <[EMAIL PROTECTED]> To: Sent: Thursday, March 16, 2006 4:48 PM Subject: RE: [AMRadio] Amplifier to use with my DX-60 > > > > >From: Alan Beck <[EMAIL PROTECTED]> > > >I would like to use a cheap am with my DX-60. > > > >An SB-200-230 seems to be a Class B amp. There for it only conducts on the > >positive going cycle. I don't mean to sound silly, but someone told me I > >could run this in SSB Mode using AM input from my DX-60, I run 100 Watts > >carrier for 400 Watts peak, now that makes sense. > > > >What does not make sense is how do I get the other side of the wave > >form The Tank??? I guess the tank. > > > > The linear will work on AM as long as you don't exceed the peak power output > rating. Exceeding the peak output rating will cause the signal to flat-top, > distort and splatter. > > Another thing to watch for is the plate dissipation of the tubes. If I > recall correctly, the SB-200 series uses a pair of 3-500Z tubes in the > final. That means you have 1000 watts of plate dissipation available. > Running AM linear @ 100% modulation will give carrier output efficiency of > about 30%. So you could run maximum 1500 watts DC input to those tubes, > with 500 watts carrier output, and 1000 watts dissipated by the tubes. With > modulation, the tubes will actually cool down slightly, since the DC input > will not vary, but the amplifier will deliver sideband power in addition to > carrier power output. So some of the input power will be converted to rf in > the sidebands instead of heat in the tube plates. > > But you also have to be careful with the power supply. AM runs at 100% duty > cycle, so the power supply in the amplifier may not be rated to run 1500 > watts continuous duty. After a few minutes, the power transformer may > overheat. In that case you will have to run it at reduced power. But be > careful that the plate efficiency does not exceed about 33%. If you run it > at too high plate efficiency, it will not leave you enough headroom to > accomodate the positive peaks, and flat-topping/distortion/splatter will > result. > > Don't worry about the missing half of the rf cycle. It works with AM > exactly the same way as it does with SSB. Since the amplifier is single > ended and not pushpull, the missing half of the rf cycle is filled in by the > "flywheel effect" of the rf tank circuit. > > In summary, with class-B linear AM operation, the final will run about 33% > carrier efficiency. The peak efficiency on modulation peaks will be about > double that, 67%. Two-thirds of the DC input to the final will be > dissipated as heat in the plates of the tubes under carrier-only, no > modulation conditions. That means the carrier output will be one half the > plate dissipation of the tubes. The peak power output should be about 4 > times the resting carrier output at 100% modulation, if flat-topping is to > be avoided. > > Linear amplifier AM operation dates back to the very earliest days of radio. > The earliest high power broadcast stations used it. It was used for years > before anyone figured out how to run audio amplifiers in class-B. Before > then, the only kind of high level plate modulation that was used employed > class A audio amplifiers, usually the "Heising" circuit but sometimes series > modulation was used. Both those systems ran at lower ovarall efficiency > than linear rf amplification. Therefore, AM linears were used long before > high level plate modulation for high powered AM transmitters. > _ > > This message was typed using the DVORAK keyboard layout. Try it - you'll > like it. > http://www.mwbrooks.com/dvorak/ > http://gigliwood.com/abcd/ > > > __ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb > >
RE: [AMRadio] Amplifier to use with my DX-60
From: Alan Beck <[EMAIL PROTECTED]> I would like to use a cheap am with my DX-60. An SB-200-230 seems to be a Class B amp. There for it only conducts on the positive going cycle. I don't mean to sound silly, but someone told me I could run this in SSB Mode using AM input from my DX-60, I run 100 Watts carrier for 400 Watts peak, now that makes sense. What does not make sense is how do I get the other side of the wave form The Tank??? I guess the tank. The linear will work on AM as long as you don't exceed the peak power output rating. Exceeding the peak output rating will cause the signal to flat-top, distort and splatter. Another thing to watch for is the plate dissipation of the tubes. If I recall correctly, the SB-200 series uses a pair of 3-500Z tubes in the final. That means you have 1000 watts of plate dissipation available. Running AM linear @ 100% modulation will give carrier output efficiency of about 30%. So you could run maximum 1500 watts DC input to those tubes, with 500 watts carrier output, and 1000 watts dissipated by the tubes. With modulation, the tubes will actually cool down slightly, since the DC input will not vary, but the amplifier will deliver sideband power in addition to carrier power output. So some of the input power will be converted to rf in the sidebands instead of heat in the tube plates. But you also have to be careful with the power supply. AM runs at 100% duty cycle, so the power supply in the amplifier may not be rated to run 1500 watts continuous duty. After a few minutes, the power transformer may overheat. In that case you will have to run it at reduced power. But be careful that the plate efficiency does not exceed about 33%. If you run it at too high plate efficiency, it will not leave you enough headroom to accomodate the positive peaks, and flat-topping/distortion/splatter will result. Don't worry about the missing half of the rf cycle. It works with AM exactly the same way as it does with SSB. Since the amplifier is single ended and not pushpull, the missing half of the rf cycle is filled in by the "flywheel effect" of the rf tank circuit. In summary, with class-B linear AM operation, the final will run about 33% carrier efficiency. The peak efficiency on modulation peaks will be about double that, 67%. Two-thirds of the DC input to the final will be dissipated as heat in the plates of the tubes under carrier-only, no modulation conditions. That means the carrier output will be one half the plate dissipation of the tubes. The peak power output should be about 4 times the resting carrier output at 100% modulation, if flat-topping is to be avoided. Linear amplifier AM operation dates back to the very earliest days of radio. The earliest high power broadcast stations used it. It was used for years before anyone figured out how to run audio amplifiers in class-B. Before then, the only kind of high level plate modulation that was used employed class A audio amplifiers, usually the "Heising" circuit but sometimes series modulation was used. Both those systems ran at lower ovarall efficiency than linear rf amplification. Therefore, AM linears were used long before high level plate modulation for high powered AM transmitters. _ This message was typed using the DVORAK keyboard layout. Try it - you'll like it. http://www.mwbrooks.com/dvorak/ http://gigliwood.com/abcd/
[AMRadio] pricing
Folks, May I share my opinion on controversial pricing? Whether or not an asking price is sincere, it can stand or fall on its own merit. If it feels ridiculous to you, others will probably feel the same way. Just get a good laugh and let it go, and try to resist the urge to utter catcalls and profanity. The end result of that kind of behavior can look nearly as silly as how the asking price hits people, believe me. If you really want to question a price, simply do so. The seller will provide an answer, and maybe more entertainment, you know ? Paul/VJB __ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
RE: [AMRadio] Class AB and B audio XFMRS
I love this stuff! John, WA5BXO -Original Message-Not in its entirety. From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Bob Bruhns Sent: Thursday, March 16, 2006 10:12 AM To: Discussion of AM Radio Subject: Re: [AMRadio] Class AB and B audio XFMRS Magnetic hysteresis is a complicating factor. When you apply a magnetic field to a magnetic material, it is partially magnetized. When you saturate it, it is strongly magnetized. When it is magnetized, it opposes the application of a reverse magnetic field, and it takes a certain reverse applied field to overcome the residual field in the material, and it takes a little more reverse applied field to reverse the residual field. This causes a timing delay in the magnetic transitions. The amount of delay depends on the applied signal level.
Re: [AMRadio] Class AB and B audio XFMRS
Magnetic hysteresis is a complicating factor. When you apply a magnetic field to a magnetic material, it is partially magnetized. When you saturate it, it is strongly magnetized. When it is magnetized, it opposes the application of a reverse magnetic field, and it takes a certain reverse applied field to overcome the residual field in the material, and it takes a little more reverse applied field to reverse the residual field. This causes a timing delay in the magnetic transitions. The amount of delay depends on the applied signal level. Even below saturation level, hysteresis causes increasing distortion as level increased, because the residual magnetization is greater at higher levels of applied magnetic field. At the same time, the magnetic transfer of the core falls off at high levels, introducing more distortion. This is why bigger iron and better iron are favored. But the windings are important too. Issues with transformer windings can really affect high frequency response. Magnetic coupling of outer windings is not as good as the coupling of the inner windings, and different "leakage" inductance results. This, and different amounts of stray coupling between windings and to ground, cause high frequency rolloff, and it causes different windings to have slightly different frequency responses and throughput time delays. In class-B operation, these effects cause distortion of high frequency signals. Half of the waveform is delayed more than the other half, and you get asymmetrical crossover distortion. This distortion sounds terrible, especially on sibilants. The two halves of the waveform may have different amplitudes as well. I have improved this distortion by adding some capacitance to the faster side at the driver level. This tends to balance the delay and eliminate this effect. When a driver transformer is used, reversal of the grid connections may help by making the unequal delays of the driver cancel those of the output stage. The plate connections to the driver transformer can also be reversed to maintain the original audio polarization, if necessary. Eddy currents in the core absorb high frequency energy. This is why we 'laminate' the core, slicing it into thin layers, and coating them with insulating paint. The thinner the layers, the less high frequency eddy current loss there will be. This is why audio transformer laminations are usually thinner than power transformer laminations. In analog magnetic recording, hysteresis causes a huge crossover gap that must be compensated, or unbelievable crossover distortion results. Modern analog recorders use about 100 KHz AC bias, adjusted slightly higher than required for maximum recorded output, to achieve minimum crossover distortion. Typically this overbias reduces sensitivity just a little bit at 1 KHz , about 0.25dB. However, it reduces higher frequencies more strongly, about 2dB at 10 KHz. This is equalized out during recording. Bacon, WA3WDR - Original Message - From: "Larry Will" <[EMAIL PROTECTED]> To: "Discussion of AM Radio" Sent: Tuesday, March 14, 2006 3:12 PM Subject: Re: [AMRadio] Class AB and B audio XFMRS > Bob and all, > > Both of our discussions are correct but deal with a different part of > the problem. Core saturation is definitely one of the problems but > hysteresis, the inability of the magnetic core to instantly change > polarity is another. The core saturation causes a spiking due to > field collapse as Bacon said but the hysteresis causes the "crossover > distortion". Both contribute to the overall distortion. Higher > quality iron and enough of it helps LF but the higher interwinding > capacitance of the larger transformers can kill HF response. Thats > one reason many audio transformers can't go even to 10 or 20 kcs. > > > > > Nothing is simple. > > Larry > > > At 03:47 PM 3/13/2006, you wrote: > >Electromagnetism really confused the early scientists. > >They thought it should behave symmetrically. That is, > >if DC passing through a coil produces a fixed magnetic > >field, they thought that a similar fixed magnetic field > >should produce DC from a coil. This would have been > >every cool, because they had permanent magnets from > >which free power could have been derived. > > > >The problem was, it didn't work that way. There is a > >story about how this problem was solved. Michael > >Faraday was trying everything; he held a magnet in > >every possible place around a coil, he tried holding > >the magnet at every possible angle and direction, etc. > >But no matter what he did, no DC came out of his coil. > > > >Finally the great scientists had had enough. I imagine > >him standing up, cursing, and throwing the magnet > >violently at the coil, in anger. > > > >But something happened when he did that. The > >galvanometer twitched when the magnet passed through > >the coil! Faraday had discovered that the magnetic > >field needed to be changing in order to produce a > >volta
RE: [AMRadio] Amplifier to use with my DX-60
Alan, most all tube type linear amps are class B, or AB and can be single ended or push-pull. In RF service the tank tuning takes care of the output wave distortion making nice pretty sine waves. Linear amps are not class C because class C is really more like a switch than an amplifier. In most class C finals you can vary the input some and it will not make any difference in the output. For this reason they or good for CW and plate modulated AM. Class C finals have a characteristic of the output following the plate supply voltage up and down linearly. If the plate supply is dropped to half the RF output voltage will drop to half, and so on. For this reason the audio is inserted in the plate power supply line, hence plate modulated. As for power levels, an SB200 is only about 3DBs better than getting rid of the control carrier modulator in the DX 60 (put it in the CW position) and building an external plate modulator for it. And it will sound a lot better. It is a really cheap project too. John, WA5BXO -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Alan Beck Sent: Thursday, March 16, 2006 8:34 AM To: Discussion of AM Radio Subject: [AMRadio] Amplifier to use with my DX-60 I would like to use a cheap am with my DX-60. An SB-200-230 seems to be a Class B amp. There for it only conducts on the positive going cycle. I don't mean to sound silly, but someone told me I could run this in SSB Mode using AM input from my DX-60, I run 100 Watts carrier for 400 Watts peak, now that makes sense. What does not make sense is how do I get the other side of the wave form The Tank??? I guess the tank. I really need to go cheap on this project. I know, you guys will probably say "go big or go home". Best 73 Alan
[AMRadio] Amplifier to use with my DX-60
I would like to use a cheap am with my DX-60. An SB-200-230 seems to be a Class B amp. There for it only conducts on the positive going cycle. I don't mean to sound silly, but someone told me I could run this in SSB Mode using AM input from my DX-60, I run 100 Watts carrier for 400 Watts peak, now that makes sense. What does not make sense is how do I get the other side of the wave form The Tank??? I guess the tank. I really need to go cheap on this project. I know, you guys will probably say "go big or go home". Best 73 Alan
