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Thread: 16uf 475v caps ok for 1966 deluxe reverb?

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    16uf 475v caps ok for 1966 deluxe reverb?

    I have a 1966 deluxe reverb on the bench in for a recap and general maintenance. I have 5 16uf 475v F&T’s on hand. Voltage tolerance too low for this amp? There’s roughly 530 volts across them. For the first, since they’re in parallel should have a tolerance of 950v, so those are fine. Should I consider dropping the voltage for the caps in series? This voltage might even be too high... for what reason? I know a load resistor will do, but is it necessary? Will probably prolong the life of the caps. I have some 22uf 500v on hand too, but will still exceed the voltage tolerance

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    "Thermionic Apocalypse" -JT nickb's Avatar
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    Have you actually measured 530V? Where and under what conditions?

    I can believe that with the standby open you might be getting toward 500V on the first parallel pair of 16uF caps. The DR calls out a 450V rating (BTW caps in parallel have the same voltage rating as a single cap, for caps in series add the voltages). So your 475V one would be an improvement. If these amps have been around for 50 years with 450V why worry about 475V? That said, if you are seeing over 475V I personally would use the 22uF 500V caps as it's well within the tolerance range of the originals.

    Don't drop the voltage. It is waste of power and will significantly reduce the power output and change the tone.

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    Yeah I actually double checked and my variac was a bit beyond line voltage. Ok, so it’s actually 480. So the parallels will get 22uf 500v and series can be these sweet 475v F&T’s thanks!!

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    I am seeing 480 on the first of the caps in series, but the voltage tolerance should tripled for these correct?

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    Only because I have 2 22uf

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    Don't forget the joker g1's Avatar
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    In parallel the voltage ratings remain the same. So five or 10 caps in parallel rated at 500V are still only rated for 500V.
    Series caps the voltage ratings add.

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    Yeah I just realized I got them mixed up! Series voltage is additive, but is that true for the first cap in series? Additively there should be a tolerance for 1425v. Is that between all of them regardless of order?

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    Don't forget the joker g1's Avatar
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    Please post schematic you are referring to. I don't see any series caps in a vintage Deluxe Reverb.
    Something like a Twin will have a 'totem-pole' arrangement at the first filter node, where two 350V caps are placed in series to make a 700V rated filter.

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    Agree with g1 -post the schematic. Your comments don't tally with anything I have.

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    I am confused by what the op means by "voltage tolerance".

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    It's weird, because it WAS working fine.....

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    Sorry for the late reply, y’all! This is the schematic I have http://www.thevintagesound.com/ffg/s...b763_schem.gif

    Voltage settled on the first cap from the choke at 460v so all in all it is within tolerance. I kind of answered my own question. I was running my variac higher than the line ac voltage here

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    Quote Originally Posted by Steelwitch View Post
    Sorry for the late reply, y’all! This is the schematic I have http://www.thevintagesound.com/ffg/s...b763_schem.gif

    Voltage settled on the first cap from the choke at 460v so all in all it is within tolerance. I kind of answered my own question. I was running my variac higher than the line ac voltage here
    OK that shows a pair of 16 uF in PARALLEL as we expect. Perhaps 30 or 32 uF caps cost too much back then, or were too large to fit in the doghouse/bathtub. There's been a case made for some other effect that's "improved" with caps in parallel instead of a single larger one, maybe you get better ESR or something like that... not much to worry about in the modern day. FWIW I often use a single 47 uF 500V cap to replace the pair. Regardless of those who complain "doesn't it slow down the electrons or somethin' like that?" Hundreds, maybe even a couple thousand of these and similar amps repaired here over the last 4 decades, no complaints yet from customers regarding vanishingly small effects. However they do like the freedom from background buzz and 120 Hz modulation of notes.

    Yes it's a good idea to test and report results with your amp plugged into standard supply voltage. To do otherwise leads us on an unnecessary, time consuming wild goose chase.

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