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I am restoring a Stromberg AU-42 - 6L6G question

I am restoring a Stromberg AU-42 and I want to keep the original can cap look. I cannot find a 50/40/30 in order to keep the 50uf cap at the cathode side of the 6L6 outputs. The circuit is push/pull (2 6L6’s) and the cathodes are tied together to 50uf/50v parallel to 200 ohm resistor to ground. I believe this is the current source for the 6L6’s. I can find a 70/40/40 and a 80/40/30 can cap. I am wondering if I can increase this 50uf on the 6L6 cathode to 80uf or 70uf. My gut says this will be okay although in the back of my head, more capacitance means more current on demand which my gut says should still be okay. I don’t want to heat up the 6L6’s. Any advice would be helpful. I really do not want to use individual caps but if I have to I will.

Thank, Tom
Epsom Repair Depot

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tommyboy60
oldhvymec
5,101 posts
 
You mean a by pass on a filter cap? They are usually pretty small right?
like .47 .22, you know .XXX  not 50 or are you talking filter caps? I agree you could go up a bit.  I'm no designer, lol, but I'm one tinkering fool sometimes.. It's the nosey mechanic in me... Can't help but think about it...  Through the years I've had to do a lot of repair work on heavy equipment, a tube amp it pretty simple in comparison. Getting it to sound the way YOU want is the real trick... You sound picky.. I'm very much so.
Never walked away without a fix, never gave up...I'm one of those for types for sure..

Orange drops, man those thing last 100 years..Silver micas, what are you going with, the same, orange drops and silver micas? MC225 use orange metalized drops, very special sound...I hate messing with them, I just usually test, them. I've found a couple in 35 years... I hate to lose that sound..

Let's see if rodman99999 will chime in..  Do you have a schemo?
elevick
2,636 posts
 
Can't you leave the caps but have all of the single once mounted underneath the chassis?  It can look neat and professional if someone ever opens it up and from the top it will all look mint.
roberjerman
4,319 posts
 
Go for the 80/40/30 cans!
bdgregory
1,710 posts
 
You should post this on The audioasylum tube diy forum. You’ll get multiple authoritative responses quickly there.

that said, if this is the cathode bias bypass cap, different values will materially affect tone. If it were me, I would not worry about using the multi section cap and mount a single cap across the bias resistor. I would buy the 70/40/40, test the 70, and compare it to a single 50uf cap (maybe other values too) mounted across the resistor.  I suspect you’ll lose bass with the higher values.
tommyboy60 OP
3 posts
 

Yes, I mean 6L6 cathode bypass cap and from what I read going from 50uf to 100uf will have very little change in response of the 6L6 but going lower than 50uf will.  Someone actually pointed me to a bypass circuit calculator and it figures it all for you.  This calculator does not have the 6L6 as choice (mainly pre-amps like 12AX7) but going from 50uf to 100uf does not change the gain and very little effect on the response.  You go under 50uf and you start to lose the low frequency response and lowers your gain.    At this point I think I am leaning toward the 10/10/10/20 and 80/40/30 can caps.  People tell me and I am in agreement that the individual caps are superior to the cans but call me anal/thorough, I would like to keep the look without the extra clutter.   Now my dilemma is replacing the current .1 Stromberg paper caps on the primary side and secondary filament side with safety caps.  Been reading about the X1/X2 and Y1/Y2 safety caps and this is my new dilemma.

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