weird cap value in schematic

[estch71]

This is more so for an amp but, just for future reference, what kind of caps have values such as 30/6, 1/15, 10/100, etc?

Here's the schem:

[slacker]

You normally see it on electrolytic caps but it could be any type. The first number is the value, you might have to work out what the units are if the schematic doesn't tell you, the second is the voltage rating. So for example 10/100 is 10uF 100 Volts.

[Mark Hammer]

I can't see the schematics here at work, but I will simply say that once upon a time, the voltage ratings of electrolytic capacitors made a difference in both size and price.  These days, a unit rated at 50V might cost a penny or two more than one rated at 35 or 16v, and might be 10% larger (though still 1/5 the size of what it would have been 30 years ago).  Feel free to use 35V caps throughout anything that is intended to use 9V, 12V, or 18V.

Cap values have changed over the years too, with greater standardization.  So you likely won't find a 30uf cap, but you will find 33uf, and without seeing the circuit in question, the chances are VERY good that value will be a quite suitable substitute...particularly since those older caps (and even many newer ones) would be +/-10% or more from the value printed on the side.

[estch71]

Thanks, Mark.  I wound up going to Mojotone and found most of the caps, which was a score.  I have to recap the amp due to the fact that I don't think it's been touched since it was made.  Hopefully I'll be able to bring back some of the tone it had.

[duck_arse]

there is only a couple of non-polarised caps on that circuit, none of them have voltage ratings given, not even in the drawing title-block thing. what would be the voltages on those ".047" caps between the 12ax7 and the ouput valves?

[estch71]

I opened the amp and saw that a good number of the caps were 600v and above, mostly Mallory types.  There are a few ceramics in there, although I can't say which ones as I don't have the amp in front of me right now.  The smaller voltage caps I'm not so worried about.  It was the higher voltage ones, especially ones like the 1000uf 30v (which I actually have for some reason), which I wanted to find and purchase.

[PRR]

> what would be the voltages on those ".047" caps between the 12ax7 and the ouput valves?

Find the "B+ cap" for the stage. Observe rating. Use at-least that much voltage rating for all signal caps in that stage.

The stage you point-at is fed from a 450V cap. 600V would be a reasonable rating.

The transistor stuff is all fed from point "A" which is a 35V cap. It would be reasonable (often very conservative) to spec 35V caps throughout the transistor-works.

There's minor contradictions. The reverb driver has a 50u 50V cap, even though it is clearly lower than point "A" 35V. I would assume that at 50u, 35V and 50V were the same price; or that UniCord had a big crate of 50u 50V for general applications. You also see 15V as a coupling-cap a few places. Since the collector is usually about half the supply voltage, and half of 35V is close to 15V, these may be correct. (OTOH, if this were in my hand, I'd poke a voltmeter in there and see if UniCord maybe built it with skimpy safety margin.)

"Q2" BC169 is clearly missing a base resistor.

That reverb driver looks like a dog's-breakfast of stray ideas.

[estch71]

There's a slew of issues with Unicord's builds.  I think they were cheaply produced.  I actually took out the reverb board, which was a bit draining on the tone overall.  I think it needed a rebuild.  In any case, I have new caps coming tomorrow, which is awesome.  Is it possible that caps can gate sound?  I've been researching this topic but haven't found any lucrative info on the subject. 

[duck_arse]

thanks prr, that 600V was the point I was driving at. I don't have a license, though. the place you would most want voltage ratings marked, they aren't.