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Organ - Allen model 20a amp

nerdorama said:
What voltage do you see at the #8 pins? Measured to ground correct?
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Good evening. I took some measurements on the amp. With 116VAC, I'm getting 6.3VAC at the heaters, grounded on the chassis. I am getting 33VDC on pin 8 of the two 6L6's.
V1 pin 1 3 6 8
80V 1.11V 87V 1.65V
V2 pin 1 2 3 6 7 8
282V 87V 97V 280V 80V 97V
V3 and V4 pin 3 4 5 8
412V 420V 0V 33V
All of these are close,m thanks to your print nerdorama. Might be light on voltage for the plates of the phase inverter. I'm getting 49 and 47 mA draw according to my bias test pro from amplified parts. Not bad for two mismatched 6L6's. I was playing my guitar through the amp with a 1x12 eminence swamp thang. Seriously considering rebuilding this into a fixed bias amp with two 12ax7's.
 
WindyJohn said:
Thanks Selmerdave and nerdorama. I've poked around inside it and I'm not getting the 35V at pin 8 of the 6l6's. But the amp works, like said before, it's quiet. I might try a set of 6l6cg's, the ones I'm using aren't GC's. Might make a difference? Have to see. Again, thanks so much for the help.
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Not GC’s but what version of 6L6s are you using? Any issues after using it for a while, especially the screens? Screen voltage is high for non-GC versions of 6L6. Does it matter with UL connection?
 
The 20 is a nice amp but has too much gain for an audio application. I restored a pair some years ago and bypassed or eliminated the input stage. Can’t remember and not home right now. Turned out very well for the owner who had Klipsch La Scala’s. They were very quiet on these high sensitivity speakers.
 
nerdorama said:
The 20 is a nice amp but has too much gain for an audio application. I restored a pair some years ago and bypassed or eliminated the input stage. Can’t remember and not home right now. Turned out very well for the owner who had Klipsch La Scala’s. They were very quiet on these high sensitivity speakers.
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Those gain mods already done on these two amps.
 
Hey @BmWr75, have your Allen type 20‘s seen daylight yet? I have an unmolested pair and would like to learn from your experience.

What exactly did you do for those “gain mods”.
 
I might jump in here on the "gain mod". The pair I did for an acquaintance years ago was to just disconnect the first stage of the 12AY7 and connect the potentiometer to the grid of the second half. I made the two amps to use opposite halves so he could swap the tubes between channels periodically and get use of both halves.

If I was doing it for myself I would likely replace the 12AY7 double triode with some single triode. Kegger did a mod like this using a 6S4 single triode.
 

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spantou01 said:
Hey @BmWr75, have your Allen type 20‘s seen daylight yet? I have an unmolested pair and would like to learn from your experience.

What exactly did you do for those “gain mods”.
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Still packed up. Kegger walked me through the gain mods via PMs. If you will PM me I'll look on my PC when I get home and see if any documentation on the mods was saved by me.
 
spantou01 said:
Thanks for the replies. @nerdorama ’s “Kegger schematic” is probably it!
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I have three different schematics that Kegger sent me 10+ years ago. See attached, original circuit, mods V1 and mods version 2.
 

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One of Kegger's original posts.

Allen 20 watt amp

Well.....I finally got motivated to start on the Allen 20 watt amps I have. I was considering modding the circiut but I've decided to give it ago stock for now. I've completed the recap on one at this time. All caps were replaced save for one that goes to the extension socket. The carbon comp...
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nerdorama said:
What voltage do you see at the #8 pins? Measured to ground correct?
Click to expand...
Good morning. Sorry about the lack of communication, I was doing more testing last night and I'm getting 33V at pin 8. I'm only running it at 111VAC.
I'm beginning to think that the input needs a preamp level to drive the power section properly. I'm planning on a re-cap before I do that. And eliminating the gyro wiring as well.
Have a good one!
 
Haha, I see now. I never noticed who posted that. It was me!! I'm guessing it needs a preamp level input to drive the gain stage before the phase splitter. Did the person who posted the gain reduction modification specify how the input was being driven?
 
In my case it was used with a line stage. What are you planning, or hoping, to use for the source signal?
 
WindyJohn said:
Haha, I see now. I never noticed who posted that. It was me!! I'm guessing it needs a preamp level input to drive the gain stage before the phase splitter. Did the person who posted the gain reduction modification specify how the input was being driven?
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Haha! I read some good posts (or bad) sometimes and then realize I wrote it!

It may be helpful to you to read through the original thread by Kegger that nerdorama linked in post #51. In the original thread post #12 Kegger wrote:
“I'm assuming your using an preamp/external volume.”
 
so these are single channel yes? Whats the other half of the 12AY7 doing? If you need more gain it seems like it would be dead simple to just use the other half of that tube to get yourself some extra gain.
 
spantou01 said:
Haha! I read some good posts (or bad) sometimes and then realize I wrote it!

It may be helpful to you to read through the original thread by Kegger that nerdorama linked in post #51. In the original thread post #12 Kegger wrote:
“I'm assuming your using an preamp/external volume.”
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Thanks. I'll give it a read.
 
If the goal is guitar amp, you probably want a full on preamp ahead of it with tone controls and all that stuff. This is just a power amp.
 
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