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Old 6th July 2006, 06:23 PM   #1
diyAudio Member
Join Date: Apr 2006
Location: Utica
Default Guitar amp input tube paralleled

Hi all

Has anybody tried using a paralleled ECC 83 (jumped pins 1 to 6, 2 to 7, and 3 to 8) as input stage of a guitar amp? I found a related thread( Massive Parallel Operating ), but it’s not guitar amp oriented and is a bit too tech for me? Would paralleling increase sensitivity, signal to noise ratio, warmth, and other such nice things. Is it worth trying for a guitar amp input stage?

Also, I noticed that most tube effects loop circuits use two gain stages, a “buffer” which lowers the signal level and then a recovery stage. What will happen if I use a resistor network (or a pot) to lower the signal level instead of the buffer? Will this work?

The reason I’m asking is because after modifying the preamp sections of a guitar amp (fender tremolux clone), I ended with half of the first ECC83 and half of the third ECC83 being unused, so wonder if I should parallel the first half with the input stage and use the other half for an effects loop recovery stage.

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Old 7th July 2006, 02:51 AM   #2
diyAudio Member
Join Date: Oct 2004
Location: Adelaide South Oz
Paralleling the input stage works well
You get 2 x the gain
1/ root 2 the noise.

You need to reduce anode load resistor to half and cathode bias resistor to half - you might also need to reduce grid stop resistor (probably 68K) to half.

You can also play with harmonic structures by using separate (original value) cathode resistor on each half (rather than connecting cathodes together) and bypassing one side with say 22uF and the other with say 0.47uF. Or even different value cathode resistors to run the 2 halves at different operating points.

Play to your hearts content.

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Old 8th July 2006, 12:03 PM   #3
diyAudio Member
Join Date: Apr 2006
Location: Utica
Thanks gingertube,

I paralleled the input tube and AUSOME, especially the OD channel - much quieter now. At lower gain settings the sound became creamier and thicker. At higher gain, I get full out skull-crushing shred that is still very quiet......just amazing

This is a great mod that I would recommend to anybody messing around with DIY guitar amps. I wonder how come parallening the input tube is not more widely used in commercial amps. As far as I know Matchless are the only amps that have it. Certainly my next project will involve using paralleled ECC83 in all preamp stages.

Does anybody have any thoughts about my effects loop question?


PS forgot to mention that I left the anode, cathode, and grid resistors as they were ...220k, 1k5, 68k. Cathode bypass cap is 680n
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Old 8th July 2006, 06:11 PM   #4
amperex is offline amperex  United States
diyAudio Member
Join Date: Feb 2005
Location: MI
Default Matchless

I believe some Matchless models do the parallel tube trick.
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