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

[Strat76]

Hi again,
FYI I followed the imaradiostar advice and I destroyed the first 5e3 I build. It didn't sound so good so, no mercy ...
I kept the power supply and put two crocos for a cap and two probes for the multimeter. So I am able to read the voltage on a 10M resistor in series with the capacitor in test. I can see if there is any leaking current. I tested about fourty PIO and the voltage on the resistor never exceeded 200mv. So the leaking current according to my calculations are very very weak. Far weaker than the I leak max of each capacitor. I tested 0.047, 0.022, 0.1uf cap.

So, for now, I assume than the nos PIO are really reliable. ;-)

Thanks again for all your precious advices.

Fabrice

[imaradiostar]

Dude, that was for testing leakage, not running an mp with unproven caps! I'm sorry if it caused your amp to fail.

Jamie

[Strat76]

Excuse me, my English is sometimes approximate ... I meant that I destroyed an old 5e3 that I built some months ago ;-)

[makepeace]

the amp didn't blow up, he just "destroyed it" ie took it apart. now could anyone perhaps answer my question above?

regards

[jmaf]

I can see if there is any leaking current. I tested about fourty PIO and the voltage on the resistor never exceeded 200mv. So the leaking current according to my calculations are very very weak.

Fabrice, if you use such a large resistor(10M) the multimeter might influence the reading.

If your +B is 500V, and you use a 1ooK resistor, the maximum wattage dissipated with a completely shorted cap would be 2.5 Watts, so if you use a 5 to 10 Watt resistor you'd be OK.

[imaradiostar]

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

Is that the question you wanted a reply to?

By reducing the value of the coupling caps between stages you achieve two things.

First, you avoid excessive bass response. Excessively large caps tend to make and amp sound "flubby" or imprecise. You can determine the "bass rolloff" using this calculator, which is using the formula:

f=1/2piRC

where f is frequency in Hertz, pi=3.14, R equals resistance in Ohms and C equals capacitance in Farads. F will be the -3dB point of the bass rolloff. Unless you have negative feedback around the power amp you can generally get away with much lower cap values than would be needed for traditional 20Hz-20kHz audio use.

Second, by reducing the value of coupling caps you're helping to mitigate blocking distortion. You can also help this by using larger value grid stopper resistors at the grid of whatever valve follow the coupling caps.

In regards to what Strat76 said- I guess you meant to say you took your 5e3 apart. I thought it had issues as a result of leaky caps!

jamie