Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: bmccowan on October 27, 2020, 09:53:15 am
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I just started rewiring an early all octal GA-40 Les Paul amp that came to me pretty rough. It has 2 chokes. I typically like to keep vintage amps mostly stock, but I also often up the filtering. In this case, I'm not very schooled in chokes and wondering if I would be better off to keep the stock filter cap values.
2 schematics, which seem to accurately reflect the amp are attached. The clear one was drawn by Jack Hester who used to contribute here.
The first filter cap is 10uf followed by a 10H choke. I was about to up that cap to 20uf, and thought I'd ask here first. should I keep that cap at 10uf since its immediately followed by a choke?
The second choke is 30H and is in the feed to the tremolo circuit and is bypassed by a 40uf 150V cap. I will keep this 40uf but up the voltage rating because that's what I have. But I am really curious about the bypassed choke. Who here can school me on this?
Thanks
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The choke and cap make up a tuned LC tank circuit that is part of the tremolo oscillator. It has nothing to do with B+ filtering. Leave the values as they are.
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What Steve said^
the PS filtering, C16,17 and L1 can be tweaked, I'd be inclined to 40uF L1 40Uf (after verifying the Rec tube datasheet)
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Thanks to both of you. I went and looked up "tuned LC tank circuit." I need to read about it to understand (Political Science major here) but will leave those values be, with a fresh cap.
And I'll up that first filter cap value within spec for the rectifier (5V4)
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Political Science major here
:l2:
I could never figure out the "science" part of that degree, so I switched to engineering, way more confusing but they do use logic :icon_biggrin:
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I think "arts" didn't want us either and there was a round of rock, paper, scissors. I loved studying politics, political philosophy, and political history; but I no longer recognize what is happening with politics.
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I was taught about thermal dynamics, I think it's reached Chaos :icon_biggrin:
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...I'll up that first filter cap value within spec for the rectifier (5V4)
No. Don't. A 3-part filter is "cubed better" than a 1-part filter. I figure less than 1V ripple, where simple cap-input filter may be 20V ripple. It is plenty clean as designed. It is over-cost, but that cost was paid in 1947 dollars and is now forgotten. The weight is still there but this is no longer a touring amp (and who tours this year?).
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Shooter - Chaos it is!
PRR - thanks. I just went out for a motorcycle ride and while riding was wondering if Steve meant to not change any of the values, or was just referring to the trem circuit. And I think I have some 1947 dollars around here somewhere, so 10uf it is.
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the great thing about Chaos, it's real easy to spot "anomalies" :icon_biggrin: