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Old 15th May 2011, 02:10 PM   #1
roline is offline roline  United States
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Default Another PCB tube amp design

I received an Email from Kegger (AK site) to see if I would be interested in a simple design that he has built modifying a ST70 chassis and PCB. I modified one of my Compactron designs, leaving the tube spacings and mounting locations the same. Each PCB could fit the same mounting top plate. My goal was to try to find the cheapest available components to try out if you scrounged around in a goal of giving newbees another alternative to limited designs for getting started in tube audio. It is quiet as a church mouse until you crank it up, minimal resistive feedback used, no dominate pole between the first and second stage currently as evaluated.
The input tubes were $1 each and the 6L6 Russian 6P3S were under $4 each delivered. The power iron was the $20 10lb'r, I had bought 3 to play with 300-330V at 200ma. The out iron that I have to choose from are all Hammond's, 40 watt 6K and 60watt 6K. Lower Raa could be used for more power output and a little distortion with a little loss of class A performance.
Voltages 310 to 365 on the outputs, 250 second stage and 210 on the input.
I added a boost iron to get the 365, The limited specs on the 6P3S suggest that do not like over 375 volts, reduced life.
IN UL the 6P3S performed quite well and sounded better balanced than the EL34's that I had ( Chinese origin). 300v was fine but better sounding at 365v.
I would have to say the same for the SV6550-C- tubes preferring 365 over 300v. The caps are stacked on the PCB so the upper limit is 600v+.
With tube availability from the 6P3s to KT88, I'l be playing with this PCB for a while, then I'l have to try it in triode mode.....
And then there are more power transformers to try out as well...
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Old 15th May 2011, 04:23 PM   #2
kevinkr is offline kevinkr  United States
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Some of those filter caps seem awfully close to the output tubes, heat being the enemy of electrolytic capacitors and all, I'd recommend mounting them on the bottom as you did on one of the boards.
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Old 15th May 2011, 07:45 PM   #3
roline is offline roline  United States
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I check parts count while acquiring components by placing the components on the top side, all electrolytics go on the bottom when installed... it is the only way to get it to install onto the top plate without lots of extra holes....... Pic of the completed compactron version attached..
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Old 15th May 2011, 09:31 PM   #4
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by roline View Post
I check parts count while acquiring components by placing the components on the top side, all electrolytics go on the bottom when installed... it is the only way to get it to install onto the top plate without lots of extra holes....... Pic of the completed compactron version attached..
Very cool! I like the look of your amplifier a lot.

Good to know that you do place the supply caps on the bottom side of the PCB.
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