Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: hatchhh on April 18, 2010, 09:54:49 am
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Hi:
I am wanting to replace the filter capacitors in the above referenced amp. I asked a general question about capacitor values before and was told it is okay to go up in voltage but typically not down. My dilemma is that the original filter caps in this amp are 20uf/600v and the size of an equivalent replacement will not fit in the tray. So I am not sure what to do, or what my options are.
As an aside, the reason I want to replace the filter caps is the current caps in there seem odd (the amp works) the first two (left most with knobs facing toward you) are 100uf/350v with 220k/2w resistors soldered to them, the balance are 500V(sorry don't have the uf value with me), the black wire from the power transformer which would normally go to the negative of the first cap, goes to the second, and then there is a jumper wire from the positive of the second back to the negative of the first. Like I said the amp works, but seems like an odd solution. One of many odd solutions under the hood of this thing.
Thanks in advance for replies.
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The 100µF 350V caps are connected in series in order to double their voltage rating: 350V x2 = 700V, while capacitance is halved: 100µF / 2 = 50µF.
The PT should be a 8087 - app 350-0-350V loaded with today's 120V mains and 450V max B+, you can safely use 500V caps.
I would remove the whole cap board, keep it if original and fit a new one using modern components.
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Hi:I am wanting to replace the filter capacitors in the above referenced amp. I asked a general question about capacitor values before and was told it is okay to go up in voltage but typically not down. My dilemma is that the original filter caps in this amp are 20uf/600v and the size of an equivalent replacement will not fit in the tray. So I am not sure what to do, or what my options are.
As an aside, the reason I want to replace the filter caps is the current caps in there seem odd (the amp works) the first two (left most with knobs facing toward you) are 100uf/350v with 220k/2w resistors soldered to them, the balance are 500V(sorry don't have the uf value with me), the black wire from the power transformer which would normally go to the negative of the first cap, goes to the second, and then there is a jumper wire from the positive of the second back to the negative of the first. Like I said the amp works, but seems like an odd solution. One of many odd solutions under the hood of this thing.
Thanks in advance for replies.
I use the sprague 500 volt caps all the time in rebuilds with no issues, these amps never needed 600 volt caps (Leo most likely got a hell of a deal on a substantial quantity!).
Sounds like someone wanted more bottom from the super, I'd return her to stock. The amp in my avatar is my '61 Super rebuilt three years ago using the above mentioned caps with no issues, one of my favorite amps of all time. :wink: