Russian PIO in a Fender Clone without testing them. Is it risky ?

[Strat76]

Hi everybody,
Once again, I need your precious advices.
I got a good stock of Russian PIO caps K40Y9. As I use them in my guitars (and I am very happy with), I am ready to put them in my next amps.
I know that they are built like a tank, and sealed, but I know also that there is a risk of leakage.
I am ready to buy a ESR meter to test them, but I can't find an ESR meter able to test below 1uf. And I plan to use these caps as coupling caps. So their values come from 0.0047uf to 0.1uf.
First I would like to ask you if it's very risky (I mean much more than a new polyester cap) to use them without testing if they are leaky ?
Second, if there is an ESR meter able to test these values.

Thanks in advance
Fabrice

[Steve Conner]

High ESR is not leakage. They're two separate failure modes that don't correlate.

To test for leakage, put a high DC voltage (a good fraction of the capacitor's rated voltage) across the capacitor and measure the current flow through it. It should be a microamp or two at worst. Unmeasurably low at best. If your meter blows its current range fuse and catches fire, the capacitor was really bad!

I don't know of a commercial instrument that does this, but if you have a homebrew amp lying half dismantled, you can use the B+ voltage.

If these are the good military grade Russian caps with sealed metal cases, it is probably OK to just install them in your amp and see if it works. The Russian military stuff was decent quality. As part of the checkout procedure for a new amp build, you'll find any leaky capacitors by the abnormal DC voltages and bad sound.

[Strat76]

Hi thanks for your answer. I think I will put them in the amps and see how it works ;-)

[hack]

I've used those Russian caps (and the other popular Russian cap) .022uF as V1 DC blocking caps in 5E3 builds. They are excellent. One of these amps was the best sounding 5E3 I've ever heard. Was likely the right combination of transformers, tubes and everything else.

[Strat76]

I've used those Russian caps (and the other popular Russian cap) .022uF as V1 DC blocking caps in 5E3 builds. They are excellent. One of these amps was the best sounding 5E3 I've ever heard. Was likely the right combination of transformers, tubes and everything else.

Yes I think it's worth it to test them in a amp. Did you test them before ?

[hack]

No testing. I just soldered them in position. No problems with any. I built three 5e3 amps with three sets of two in the V1 place. I have another set of two caps remaining in my stash (the smaller size ones) I will use for another build. The four big ones I had I used. Sold the amps. Never had any complaints.

Again. One of the amps was the sweetest most toneful beast ever.

You can order them cheaply in quantity from Russia. Or you can buy them in small quantities on ebay from a guy who gets them wholesale from Russia.

[Strat76]

No testing. I just soldered them in position. No problems with any. I built three 5e3 amps with three sets of two in the V1 place. I have another set of two caps remaining in my stash (the smaller size ones) I will use for another build. The four big ones I had I used. Sold the amps. Never had any complaints.

Again. One of the amps was the sweetest most toneful beast ever.

You can order them cheaply in quantity from Russia. Or you can buy them in small quantities on ebay from a guy who gets them wholesale from Russia.

Many thanks, that reassures me

[Strat76]

No testing. I just soldered them in position. No problems with any. I built three 5e3 amps with three sets of two in the V1 place. I have another set of two caps remaining in my stash (the smaller size ones) I will use for another build. The four big ones I had I used. Sold the amps. Never had any complaints.

Again. One of the amps was the sweetest most toneful beast ever.

You can order them cheaply in quantity from Russia. Or you can buy them in small quantities on ebay from a guy who gets them wholesale from Russia.

Excuse me, but you say you never had any complaints but do you mean from your customers ? Can you say these caps behave well with time ?

[diagrammatiks]

those caps are great for the most part.

lots of people have used them for hifi with very few complaints.

[jmaf]

I learned a trick from R.G. on this forum. Put a resistor in series with the capacitor, using the rated DC voltage. If it develops a voltage across the resistor(Edit: after it's charged), it's a leaking capacitor.

That way there's no series measurement and the ammeter won't blow up if the camp is shorted. I made myself a jig for this, high voltage DC supply, a 100K resistor and two clips. I clip the capacitor under test and turn on the DC and wait a bit, then measure the voltage across the 100k.

[Strat76]

Thanks for the trick. I will do it as soon as I can put my hands on a DC supply.

So for those who can be interested in, I put the PIOs without testing them in a new amp, and it works perfectly. Great sound. Great OD. No Harshness. Just the fu... annoying bass when the volume is cranked, as usual ;-)

Anyway thanks for all your answers.

[imaradiostar]

no special DC supply needed- any tube amp B+ supply will do. Any old tube amp PT hooked to rectifiers and a cap for that matter.

jamie

[hack]

If you haven't tried it, using .022uF DC Blocking caps in V1 (and V2 also for that matter), will rid unwanted boominess.

[makepeace]

hack, by V2 do you mean the decoupling cap between the 12AX7 triode gain stage and the PI?

also, would changing the power tube couplers to a lower value have a potentially desirable effect?

cheers

[Strat76]

If you haven't tried it, using .022uF DC Blocking caps in V1 (and V2 also for that matter), will rid unwanted boominess.

Thanks Hack but I have already 0.022uf in V1 and 0.047uf in V2. It's almost perfect but when the volume is cranked, I mean full cranked, there is always too much bass. I will try 4uf for the bypass cap in V1.