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LuckyLyndy 26th November 2011 06:12 PM

Cap question, similar values
Please forgive this question:
I broke off the cap attached to my NOS power switch, and think these are the values I read.
From the original power switch, the value

The new NOS cap reads, (I think)
BC Z5U 1.03M 1 kV

Do these seem similar? Am I reading the second one incorrectly?

Of course, the only decent electronic shop in Utah is closed for the holidays this weekend, so it is the Radio Shack for me. What values can I go with that will work with this? I assume it is just used to block the surge and protect the speakers, right?
Thanks again.
Clueless but not solderless in Utah

thaumaturge 26th November 2011 06:59 PM

Hello also from Salt Lake. The cap on the power switch likely helps prolong the life of the switch by suppressing contact arcs. The second listed is not the same. The first is a 0.01uF and the second a 1.03 (or just over a hundred times the value.)
Unit should function fine without the cap till Monday.

LuckyLyndy 26th November 2011 07:29 PM

Thanks, Doc
Was hoping to get it all done today.
I knew they couldn't be the same value...but both toggle type power switches were original
for this Dynaco PAT-5, and then changed by Frank VanAlstine to a Transcendence Series Two preamp. Circa 1986
One board next to the trannie was a bit scorched. I asked Frank about it...

Later we found a better way of getting rid of the excess voltage and heat. We simply wired the power transformer for 240V operation. Then when used on 120V as intended, this cut the operating voltage in half and made the output of the power transformer much easier to manage without the need for huge high wattage hot running power resistors.

Which I think my electronic friend and I can figure partly, but my friend had this question for Frank:
I suspect that if you drop the power transformer output voltage, then you'll want to reduce the value of the power resistors as well. Did Frank give you new values for that?
No answer from Minnesota. The wind blows cold and empty...

indianajo 26th November 2011 07:49 PM

Modern caps are marked with 2 significant digits and a power of 10 in picofarads. So your new cap, if it doesn't have a decimal point (it probably doesn't) is 10*10^3 picofarads, or 10000 picofarads, or 0.01 microfarad. Same value. Modern "M" is a voltage rating, pretty high one. The old "M" is microfarads, replaced since about 1980 with a "u" which is not greek to me. Modern practice is to use a UL rated "X2" cap for switch bypass, but the old way is to put a 1000 V rated cap on the switch. You can get 600 V transients on the 120 vAC line, is why the 1000V rating. I lost a 1000V rated .01 uf across my power switch probably due to lightning years ago, also bridged the switch (toasted plastic) but no damage to the PAS2 power transformer.
Z5U is the type of ceramic insulator, a budget one but stable capacitance over temperature is not required for a function like this.

thaumaturge 27th November 2011 04:03 AM

I stand corrected.

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