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Author Topic: Using Collins 30 L-1 amplifier for AM  (Read 4160 times)
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ko4ctm
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« on: December 09, 2023, 05:28:46 PM »

Let me start by introducing myself. This is Jim from Climax NC KO4CTM. This is my first post in the forums.

I just started dabbling in AM using my old Heathkit DX40 and Hallicrafters HA-5 and HT-40. Iíve only made a few contacts, but have enjoyed venturing out into AM. Most of the time, I operate CW.

I also have a Ten Tec Century 21 and Jupiter along with a Yaesu 991A and Johnson Viking Adventurer.

I have a good friend that has offered a Collins 30 L-1 amplifier for my use, but was just not sure if it could, OR should be used on AM.

I know the manual saysÖÖ.. NO, but thought I would defer to those with much more experience than myself.

Can this amp be used for AM at all?

I know I can use it for my SSB rigs and CW.

If not, what should I be looking for to help out on the AM side?

Thanks for any help.
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Pete, WA2CWA
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« Reply #1 on: December 09, 2023, 06:11:22 PM »

Google: can you use a collins 30L1 on am
And you get, just listing two (you can pick out the rest).
https://owenduffy.net/tx/30L1/AM.htm
http://amfone.net/Amforum/index.php?topic=31320.0

And Google says:
"Tuned / loaded for AM If the PA is tuned / loaded for a little over 500W PEP (say 510W) with the least drive, the PI coupler is adjusted for the optimal resonant load for AM within the dissipation limit. AM drive is then adjusted for 123W carrier output, and modulation will take the signal to 492W PEP."
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W1ITT
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« Reply #2 on: December 09, 2023, 06:36:14 PM »

J wouldn't worry so much about the anode dissipation of the 811s as much as I would about the integrity of the HV transformer.  Those table top amplifiers had to cram everything into a relatively small box and the sizes of components had to be small to keep it within the desired footprint.  I think it was in an edition of the West Coast Handbook that I saw a chart relating the weight of a plate transformer to its power capability, given typical manufacturing practices.  Bigger is better and it's fairly linear as a generalization. 
If you cook that transformer, you now have a grey door stop.  I bought
 a Henry 1kD5 carcass with a nuked HV transformer.  The space for the original wasn't much bigger than my fist. It's not an uncommon situation with 1KD5s, sadly.   I have acquired a slightly larger transformer that I can stuff in the void and change the rectification to voltage doubler instead of bridge and it'll work OK but it won't be a barn burner.  If you run the 30L1 on AM, resist the temptation  to load it up far, and don't make long Old Buzzard transmissions like some of the boys running big iron and having a big spare parts stash out in the shed.  However, that 30L1 would be swell on CW and would appreciate a warm home.
73 de Norm W1ITT
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n8fvj
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« Reply #3 on: December 09, 2023, 08:42:58 PM »

Collins 30L-1 cannot perform AM due to the weak 811A tubes. Even lower wattage carrier at 150 watts is damaging as the tube lose efficiency at lower wattage. Install four 572B tubes and you can have a 200 watt carrier on AM.
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WQ9E
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« Reply #4 on: December 09, 2023, 09:33:45 PM »

Jim KO4CTM,

I wouldn't use the 30L-1 with a full carrier AM rig like a Ranger or DX-100 however your DX-40 uses controlled carrier modulation so the carrier level follows the average of the audio level and drops to around 10 watts output during pauses in speech.  This provides a far lower duty cycle than typical plate modulated, full carrier rigs and it is much kinder to light duty linear amplifiers.

With the DX-40 and most vintage linear amplifiers you could run them near their SSB ratings without concern.  With the 30L-1 and its lightweight power transformer, I wouldn't run it at where peaks are more than 75% of the rated CW output. 

I wouldn't run the 30L-1 at all for full carrier AM, it isn't a good amp for that choice.  Changing the output tube type isn't going to help with this because the power transformer is the weak link in a 30L-1.  The only linear amp I own that I would feel safe running legal limit full carrier AM for long transmissions is my homebrew amp which uses three 4CX800 tubes with plenty of air cooling and a 4KW CCS rated P Dahl transformer.  But I wouldn't hesitate to run my Drake L-4B at its rated 2KW PEP input when being driven by a controlled carrier T-4X series transmitter.

Rodger WQ9E
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ko4ctm
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« Reply #5 on: December 10, 2023, 08:15:34 AM »

Thank you all for the replies, and the info. I appreciate the help on something I donít have a lot of knowledge about.

I have only been a Ham about 5 years and have always just run barefoot so amplifiers is something totally new to me.
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n8fvj
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« Reply #6 on: December 10, 2023, 10:09:05 AM »

The Collins 30L-1 has a 19lb transformer. It is large enough for 200 watt carrier with 800 watt PEP out at 50% duty cycle.
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WQ9E
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« Reply #7 on: December 10, 2023, 12:28:01 PM »

A Collins 30L-1 won't even do 800 watts output on SSB without overload and excessive distortion.  With typical class B efficiency coupled with losses in the output network, it will have to develop over 1,400 watts input to provide 800 watts output.  Collins specs call for a nominal 600 watts output with 1,000 input or 60% efficiency.

Switching to 572B tubes doesn't solve that issue because these tubes were designed for higher plate voltage to approach their maximum output ratings, NOT the 1,600 volts the 30L-1 provides under load.  Amps designed around twin 572B tubes run over 2,000 volts on the plates to reach the rated 1,200 watts PEP input, not the 1,600 volts of the 30L-1 designed around 811A tubes and in those amps (i.e. Heathkit SB-200, Yaesu FL-2100B) you still won't get 800 watts PEP output when running at rated input.

The Collins 30L-1 is an excellent amp when used as designed and it will work pretty well with controlled carrier AM rigs (like the DX-40) to provide some increase in power for AM. 

Weight is not a good indicant of how a transformer will handle high duty cycle operaton.  Core material, primary efficiency, number of other windings (filament etc.), and the case/mounting system all drive performance and weight.  Ambient temperature/cooling is also a major factor in how it will handle the load of increased duty cycle operation.  A Heathkit SB-220 will withstand abusive operation much better when run without the outer case which allows it to better reject heat developed in operation and its plate transformer will withstand much more demanding conditions that way than it does when packaged as designed. 

A Drake L-4B is a good example of a robust design and will easily run 1KW RTTY input.  It uses proper chimneys and a blower with its 3-500Z tubes and an external power supply that supplies only HV (filament and bias transformer is on the RF chassis).  Its plate transformer is twice the weight of the 30L-1 combined transformer and yet even with this transformer and well cooled heavy transmitting tubes, Drake restricts full carrier AM to 500 watts in / 300 watts out.  They designed and rated it for proper operation without stressing any components.

Design engineers actually know what they are doing and they understand what they designed is a system.  Changing one part doesn't change the other original design constraints because it is a system, not just a collection of discrete components.

Rodger WQ9E
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« Reply #8 on: December 10, 2023, 01:26:58 PM »

I once owned a Collins 30L-1 (round emblems with Teflon wire) with stock 811As.

To allow for decent positive peaks and cleanliness on AM,  I found 600 watts pep was the absolute maximum out before distortion.  Thus, about 100 watts of carrier (100W carrier X6) was a good AM carrier level output. (They have marginal side-fan cooling.)  If you have low positive peaks then 125W carrier can eek out the 600W pep.  Adjust all parameters for the best heat, cleanliness and highest peaks. Adding some diodes in the cathode CT for better AM efficiency will help.

*The Collins 30L-1 does make a good IPA driver for a big power grid, cathode driven tube, like a YC-156, etc.... :-)

That said, for a stand-alone linear amplifier, I must agree that the Drake L-4B is an excellent choice using a pair of 3-500Zs.  250 watts of AM carrier at 1500W pep is a good level. (peaks are conservative X6 carrier)  They did it up right.  The L-4B market price usually reflects this quality, but well worth it. You must look around for good prices. I know a number of friends running them and they are all very pleased; to the point of bragging about them...

T

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n8fvj
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« Reply #9 on: December 10, 2023, 05:18:55 PM »

A Collins 30L-1 won't even do 800 watts output on SSB without overload and excessive distortion.  With typical class B efficiency coupled with losses in the output network, it will have to develop over 1,400 watts input to provide 800 watts output.  Collins specs call for a nominal 600 watts output with 1,000 input or 60% efficiency.

Switching to 572B tubes doesn't solve that issue because these tubes were designed for higher plate voltage to approach their maximum output ratings, NOT the 1,600 volts the 30L-1 provides under load.  Amps designed around twin 572B tubes run over 2,000 volts on the plates to reach the rated 1,200 watts PEP input, not the 1,600 volts of the 30L-1 designed around 811A tubes and in those amps (i.e. Heathkit SB-200, Yaesu FL-2100B) you still won't get 800 watts PEP output when running at rated input.

The Collins 30L-1 is an excellent amp when used as designed and it will work pretty well with controlled carrier AM rigs (like the DX-40) to provide some increase in power for AM. 

Weight is not a good indicant of how a transformer will handle high duty cycle operaton.  Core material, primary efficiency, number of other windings (filament etc.), and the case/mounting system all drive performance and weight.  Ambient temperature/cooling is also a major factor in how it will handle the load of increased duty cycle operation.  A Heathkit SB-220 will withstand abusive operation much better when run without the outer case which allows it to better reject heat developed in operation and its plate transformer will withstand much more demanding conditions that way than it does when packaged as designed. 

A Drake L-4B is a good example of a robust design and will easily run 1KW RTTY input.  It uses proper chimneys and a blower with its 3-500Z tubes and an external power supply that supplies only HV (filament and bias transformer is on the RF chassis).  Its plate transformer is twice the weight of the 30L-1 combined transformer and yet even with this transformer and well cooled heavy transmitting tubes, Drake restricts full carrier AM to 500 watts in / 300 watts out.  They designed and rated it for proper operation without stressing any components.

Design engineers actually know what they are doing and they understand what they designed is a system.  Changing one part doesn't change the other original design constraints because it is a system, not just a collection of discrete components.

Rodger WQ9E
Ameritron AL-811H sells the AL-811H with four 572B and it meets FCC requirements for IMD. It is also rated at 800 watts PEP out with a 17lb transformer.
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n8fvj
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« Reply #10 on: December 10, 2023, 05:21:58 PM »

I once owned a Collins 30L-1 (round emblems with Teflon wire) with stock 811As.

To allow for decent positive peaks and cleanliness on AM,  I found 600 watts pep was the absolute maximum out before distortion.  Thus, about 100 watts of carrier (100W carrier X6) was a good AM carrier level output. (They have marginal side-fan cooling.)  If you have low positive peaks then 125W carrier can eek out the 600W pep.  Adjust all parameters for the best heat, cleanliness and highest peaks. Adding some diodes in the cathode CT for better AM efficiency will help.

*The Collins 30L-1 does make a good IPA driver for a big cathode driven tube, like a YC-156, etc.... :-)

That said, for a stand-alone linear amplifier, I must agree that the Drake L-4B is an excellent choice using a pair of 3-500Zs.  250 watts of AM carrier at 1500W pep is a good level. (peaks are conservative X6 carrier)  They did it up right.  The L-4B market price usually reflects this quality, but well worth it. You must look around for good prices. I know a number of friends running them and they are all very pleased; to the point of bragging about them...
A Drake L4-B can only generate 1000 watts PEP output on AM, not 1500 watts PEP.
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K1JJ
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« Reply #11 on: December 10, 2023, 08:32:28 PM »

A Drake L4-B can only generate 1000 watts PEP output on AM, not 1500 watts PEP.
-----------------------


A pair of 3-500Zs will actually do 2,000 watts pep output with 3500V HV and a good tank efficiency.  

The mode does not matter; 1500W pep output is good for AM, CW or SSB.  The real goal is to determine how much instantaneous PEAK power the amplifier will put out and still remain clean.  A single 1 KHz audio tone on AM with a good scope and accurate reading peak wattmeter will tell the story.

Then, for AM, divide the peak power capability by 6 to determine the appropriate carrier level.  This is a combination of keeping the amplifier cool with clean positive peaks. So, for 1500W pep / 6 = 250 watts AM carrier. A well cooled pair of 3-500Zs will run FB at a conservative 250W AM carrier at 1500W pep output.  The peak power will then be determined by the audio level and asymmetry of your voice achieving a dynamic carrier to peak power ratio.

T
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n8fvj
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« Reply #12 on: December 10, 2023, 11:08:55 PM »

A Drake L4-B can only generate 1000 watts PEP output on AM, not 1500 watts PEP.
-----------------------


A pair of 3-500Zs will actually do 2,000 watts pep output with 3500V HV and a good tank efficiency.  

The mode does not matter; 1500W pep output is good for AM, CW or SSB.  The real goal is to determine how much instantaneous PEAK power the amplifier will put out and still remain clean.  A single 1 KHz audio tone on AM with a good scope and accurate reading peak wattmeter will tell the story.

Then, for AM, divide the peak power capability by 6 to determine the appropriate carrier level.  This is a combination of keeping the amplifier cool with clean positive peaks. So, for 1500W pep / 6 = 250 watts AM carrier. A well cooled pair of 3-500Zs will run FB at a conservative 250W AM carrier at 1500W pep output.  The peak power will then be determined by the audio level and asymmetry of your voice achieving a dynamic carrier to peak power ratio.
At 250 watts carrier any peak over 1000 watts is over 100% modulation. 100% modulation is four, not six times the carrier. The L4-B does not have 3500 volts on the plates. The Drake L4-B produces about 2750 volts. The Drake can only produce 1200 watts out with 100 watts drive.
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K1JJ
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« Reply #13 on: December 11, 2023, 02:19:08 AM »

N8FVJ said:   "At 250 watts carrier any peak over 1000 watts is over 100% modulation. 100% modulation is four, not six times the carrier. The L4-B does not have 3500 volts on the plates. The Drake L4-B produces about 2750 volts. The Drake can only produce 1200 watts out with 100 watts drive."

-----------------------
I have 3500V on my pair of 3-500Zs and they will do 2KW pep out. But I am trying to talk in general terms so that this discussion can be applied to any linear setup.

You are limiting yourself by thinking in terms of only 100% positive peak AM modulation or X4.

The negative peaks should be limited to less than 100% using a neg peak limiter. But the positive peaks can be well over 100%.  Most male voices have natural asymmetry that is over 100% positive... some can be 120% - 140% positive. (or more) This requires a linear (or any transmitter) headroom of X5, X6, etc. to accommodate. You can stop this asymmetry with an all-pass phase rotator audio circuit and keep the audio -99% negative and 100% positive.   Or run it natural with -99% negative and 120%+ positive, etc.  

The point is if you allow just X4 headroom from carrier to peak power, then any natural peaks above positive 100% will flat top and cause distortion and splatter.

So if your 3-500Z amplifier is only capable of 1200 watts pep, then the carrier must be 1200W / 6 = ~200 watts to allow for most mens' voice asymmetrical peaks.  Once this asymmetry is determined, you can fine tune the carrier to allow for the biggest  carrier with nice rounded peaks... no flat-topping.

We once did an experiment with six hams in person. There was a mic set up into a scope with a phase A - phase B polarity switch. Each took a turn talking and recording his own natural asymmetrical data.  The readings ranged from 110% all the way up to 140% positive. IE, each ham would have to use a different divisor (peak power / divisor) to allow for the proper peak power headroom.

As you can see, each AM system needs to be tailored to each particular voice. Some guys like big positive peaks - while others would rather have +- 100% phase rotator scrambling.

Once you spend some time fine tuning and setting up your audio, you will understand what I am saying and tailor your overall system to  improve your own "sound" and goals.

T
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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed.  Easily done in DSP.

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« Reply #14 on: December 11, 2023, 07:47:49 AM »

A Drake L4-B can only generate 1000 watts PEP output on AM, not 1500 watts PEP.
-----------------------


A pair of 3-500Zs will actually do 2,000 watts pep output with 3500V HV and a good tank efficiency.  

The mode does not matter; 1500W pep output is good for AM, CW or SSB.  The real goal is to determine how much instantaneous PEAK power the amplifier will put out and still remain clean.  A single 1 KHz audio tone on AM with a good scope and accurate reading peak wattmeter will tell the story.

Then, for AM, divide the peak power capability by 6 to determine the appropriate carrier level.  This is a combination of keeping the amplifier cool with clean positive peaks. So, for 1500W pep / 6 = 250 watts AM carrier. A well cooled pair of 3-500Zs will run FB at a conservative 250W AM carrier at 1500W pep output.  The peak power will then be determined by the audio level and asymmetry of your voice achieving a dynamic carrier to peak power ratio.
At 250 watts carrier any peak over 1000 watts is over 100% modulation. 100% modulation is four, not six times the carrier. The L4-B does not have 3500 volts on the plates. The Drake L4-B produces about 2750 volts. The Drake can only produce 1200 watts out with 100 watts drive.

Sigh


https://youtu.be/cajJYlqSv6Q?si=2fFBvE83hdZ0EAZw

The bird is in peak mode with a 250 watt slug.  The B&W is an avg reading meter.

The scope speaks for itself.

Please explain where it's wrong.

Almost every male has an assymetrical voice print.  Ergo, you need positive peak headroom.  Phasing is of huge importance as well.

On an utterly stock rice box with no ALC I can easily make 175 watts pep from a 30 watt carrier, no outboard processing, just watching the scope for baseline.

Had I limited it to your textbook, I'd be at 100 pct positive peaks and 60 pct negative.

Wouldn't be that loud or have any punch to it.  Phased incorrectly it would be tons worse.

Don't generalize.

--Shane
WP2ASS / ex KD6VXI
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« Reply #15 on: December 11, 2023, 12:29:36 PM »

I just picked up a AL-82 at the hamfest last week for a very good price. It's the older one with the Peter Dahl transformer, 3600 V no load. Right at 2kw on SSB PEP on the Yaesu YS-2000 or the MFJ giant peak meters calibrated to the Bird.

Driving it with my custom modulator Icom 756 pro with peaks Op amp limited to 125 percent positive, 95 on neg & phase correct for my voice, 300 watts carrier gives me 1500 watts peak plus. Will go more but that good enough power and I don't do old buzzard key downs.

Shane , your right on rice box's. There not 100 watt radios, they are only 100 watts because thats were the ALC threshold (power control) is set by the factory. The PA will do way more as you know. My Icom 756pro with the ALC cut loose (just on AM only and 455khz drive controlled by my external modulator) will peak easy to 175 watts with a stout 14 volt supply & 35 watts carrier. That's on 40 & 75 meters only, does less as you go up in bands.

My 940 kenwood will do way over 225 watts peak AM with the MRF422 but power supply limited in that radio. Same finals as the Yaesu FT-1000D runs factory at conservative 200 watts all modes, except AM at 50 watts.

I run asymmetrical mod myself, truthfully it's only a little bit louder say at 150 percent. You can hear in that video it's gets louder but not much and heard the same on the Youtube Asymod guy vids. I just stay at 125 percent because the average is better ( more than 125 just eats up to much peak Amp power) and I like to see the meter Swing !! LOL  
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K1JJ
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« Reply #16 on: December 11, 2023, 01:15:23 PM »

John said:

"
I just picked up a AL-82 at the hamfest last week for a very good price. It's the older one with the Peter Dahl transformer, 3600 V no load. Right at 2kw on SSB PEP on the Yaesu YS-2000 or the MFJ giant peak meters calibrated to the Bird.

Driving it with my custom modulator Icom 756 pro with peaks Op amp limited to 125 percent positive, 95 on neg & phase correct for my voice, 300 watts carrier gives me 1500 watts peak plus. Will go more but that good enough power and I don't do old buzzard key downs.

Shane , your right on rice box's. There not 100 watt radios, they are only 100 watts because thats were the ALC threshold (power control) is set by the factory. The PA will do way more as you know. My Icom 756pro with the ALC cut loose (just on AM only and 455khz drive controlled by my external modulator) will peak easy to 175 watts with a stout 14 volt supply & 35 watts carrier. That's on 40 & 75 meters only, does less as you go up in bands.

My 940 kenwood will do way over 225 watts peak AM with the MRF422 but power supply limited in that radio. Same finals as the Yaesu FT-1000D runs factory at conservative 200 watts all modes, except AM at 50 watts.

I run asymmetrical mod myself, truthfully it's only a little bit louder say at 150 percent. You can hear in that video it's gets louder but not much and heard the same on the Youtube Asymod guy vids. I just stay at 125 percent because the average is better ( more than 125 just eats up to much peak Amp power) and I like to see the meter Swing !! LOL  
"



------------------------------------

John,

You're doing everything right for the choice of running bigger positive peaks. I'll bet your rigs sound great.

The outboard  455 KHz balanced modulator is something I also did for my FT-102 rigs.  I also have an FT-1000D with the internal balanced modulator directly fed with audio.  DC to light and the ability to run unlimited positive peaks if desired.

These days I run most plate modulated rigs with a limit of 120%- 140% positive to allow for the guys with diode detectors and the QSB selective fading of AM/ high positive peaks.

There will always be a debate of which to choose: high positive peaks or symmetrical  phased-rotated +- 100%.  They both work FB, though I personally choose to go the natural positive peaks route most of the time.

T
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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed.  Easily done in DSP.

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« Reply #17 on: December 11, 2023, 01:35:43 PM »

Factory stock transmitters on AM do not perform over 100% positive modulation with less than 100% negative modulation. Your modified transmitters are confusing some Hams.
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« Reply #18 on: December 11, 2023, 01:43:21 PM »

Interestingly, seems a lot of my working stuff shouldn't. (according to some)
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« Reply #19 on: December 11, 2023, 03:00:47 PM »

Factory stock transmitters on AM do not perform over 100% positive modulation with less than 100% negative modulation. Your modified transmitters are confusing some Hams.

If you are confused, ask a question. The one/two liners aren't making much of an impression.
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« Reply #20 on: December 11, 2023, 04:15:17 PM »

Hey Tom

Thats cool you have a 1000D. I had one years ago and it performs great on AM with a few mods, I still have my FT-990 which is just about the same in the AM transmit circuit. Yes my 756pro sound very nice and get excellent audio reports with it. Only the absolute best Class E and plate transmitters are as good. It's all in the modulator and external audio gear, the radio is just a chain of linear amps with a frequency conversion to wherever I want to talk. Any radio with a transmit 455 IF would sound exactly the same.

I also have a FT-102 with the AM board and its sounds super with that factory TA7069 two quadrant multiplier modulator. Low level AM is easy to get nice super clean audio, one of the key's and I'm sure you know, Is you need to have negative mod limiting so the balance modulator does not phase invert and produce wavelet distortion that is normal for all four quadrant multiplier which any SSB modulator is.

Two quadrant multiplier modulator like whats on the factory FT-102 AM board does not have that issue and acts exactly like plated modulation on the scope were the carrier pinches off. The other issue is low efficiency, not so much in the radio, it can take it easily ... But in the linear amp. So you need a hefty amp to run a decent carrier with some key down time.
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« Reply #21 on: December 11, 2023, 04:25:16 PM »

I really like my Yaesu FT-1000D but the person who wrote the operating manual didn't understand the transceiver.

If either CW or AM is operated as stated in the manual, the transmitting results aren't great.  Yaesu has you adjust the RF output level control (basically a fast acting hard limiter) to set desired power output and then increase drive so that the ALC meter deflects to midscale.  This results in generating key clicks on CW and pretty much no upward modulation on AM.

Bringing ALC into action for either mode doesn't work well.  For CW and AM, set the output control so that it will have no impact upon the signal and use the drive control to set desired output level on CW or a safe carrier level on AM.

The only thing I use the output level (really limiter would be a better term) to do on Yaesu rigs of that era is to limit drive to a safe level for some amps that are easily damaged by overdrive.

Rodger WQ9E
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« Reply #22 on: December 11, 2023, 04:42:56 PM »

On the 1000D the RF power control sets the ALC threshold & transmit gain to control the power output. The drive control adjust the gate voltage on Q2036 3SK74L for CW carrier, RF processor output on SSB and AM carrier.

Correct operation for the radio is to set the power control wide open on AM so the radio can do 200 watts and adjust the drive control for 40 to 50 watts carrier. Then adjust mic gain so it kicks up a little ALC. Then your peaks will be at 200 watts , 100 percent mod

But with out external audio gear, compressor or clipper or both, its impossible to control the audio from phase inverting. You will have low average audio. But set up correctly with external gear it can sound unbelievable good and powerful. But just plugging a mic into a stock radio, it's lame.

The only newer type radios that Yaesu made that was set up correctly for AM is the FT-990 and they incorporated a audio clipper Toshiba TA7060AP that only was activated on AM and added a long time constant on the ALC circuit so the radio did not backward swing and that radio sounds great with just a 10 meg buffer amped D-104. I believe they did that so it would be popular on the CB bands.

The FT-One back in 1981 also used the same Toshiba TA7060AP clipper in it too with a Motorola MC1496 as a totally separate AM modulator. I have a mint condition latest serial number FT-One myself. The FT-102 with the stock AM board TA7069 modulator ( single gilbert cell ) is the best of them all after adjusting the differential bias for extended positive peaks.
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K1JJ
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« Reply #23 on: December 11, 2023, 05:26:10 PM »

Rodger and John,

FB on the FT-1000D, FT-990, etc., comments.  Your last few posts are filled with excellent suggestions and a road map to getting some of these older rigs to play well on AM.

Yes, the FT-1000D does need some tweaking to make AM work right.  And yes, that "wavelet" AM problem is a common issue with most balanced modulator rigs.  There are a few guys who have made up solutions to make it work like regular plate modulation as you said.  I think Steve/QIX made a little board for Bob/KBW that let the FT-101E modulate like a plate modulated rig.

I once built a plate modulated "upside-down" pair of 4-1000As in a class C AM final. It used a pair of 3CX-2500F3s modulators for huge positive peak audio capability. It was actually a high level balanced modulator.  It ran beautifully, but I could never understand why there was a bit of distortion whenever I went above 100% positive. Alas, it was the balanced modulator wavelet/crossover problem!  I experienced it again years later until I finally figured it out... :-)  (But it did sound great on a receiver sync detector at 180% positive - however, only a few guys had sync detectors years ago.)

But for a regular AM modulated rig, there's nothing like a negative peak limiter holding the neg peaks below -99% and letting the positive peaks fly where they may, based on your natural voice. No wavelets, just a carrier and audio peaks with clean crossover.   We need to keep an eye on crossover distortion too. This can be generated in the linear amplifier or in any modulator -  right along with peak distortion.

Again, getting an AM rig to function perfectly can take some time and experience.  Even the newest SDR rigs and SS amplifiers need us to pay the price in time and frustraton... It's easy to spend a lifetime playing with software. But it's hard to beat the pre-distortion "pure signal" RF negative feedback software stuff these days.

T
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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed.  Easily done in DSP.

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« Reply #24 on: December 11, 2023, 06:30:30 PM »

I have a few friends running the pre-distortion "pure signal" stuff on SSB. It's very impressive to watch the waterfall on my SDR Play and see it so perfect and somewhat sterile. I might get into that eventually but my stuff is clean enough on both SSB and AM I don't get crazy about it. Actually a little bit of splash on the waterfall adds a little character to my signal LOL !!

For real tight peak limiting I find these shunt diode clipping circuit with op amp to compensate for the diode's knee work great. All these circuits, you can adjust the positive and negative audio clipping independently very important. All except one need a split power supply.

The one I use is close to these, ( I never built these ) but I made some changes. One day I draw up a schematic on mine I use TL-072 for op amps. I like that these shunt clippers do nothing to the audio until the diode/op amp activate.  They are like precision clipping switches. Under the clipping threshold they do nothing, over a just a little they clip and dead stop the audio. It's interesting to watch on the audio scope.

I use my Alesis 3630 to drive the clipper, the 3630 is a super fast VCA peak compressor with 100us attack time but as normal still has overshoot. I only run about 2 to 3 db max of clipping. At those levels the audio still sounds clean, but the positive and negative audio control is perfect and that solves all the negative wavelet problems on the SSB type modulators.  This is all the same stuff that Orban, Inovonics, Dorrough and the rest use in the analog days before DSP. In fact I got lot of ideas from Dorrough DAP 610 & 310


* Op Amp Clipper.jpg (57.61 KB, 610x616 - viewed 55 times.)

* Fast precision clipper Shunt Type.JPG (65.23 KB, 1187x732 - viewed 52 times.)
* Audio Clipper Op amp type.pdf (221.46 KB - downloaded 28 times.)
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