• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Is this cap ok for audio?

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#3
Looks like a motor start or snubber capacitor. (or SCR phase control cap?) It's a 250V~ rated AC cap, but I sure wouldn't trust what appears to me to be a 1/4W resistor, probably rated for much less than this. I would definitely remove in this instance, also I would keep the dc across this cap to no more than say 300Vdc to play it safe.

I assume you were joking about bleeder resistors? I generally use them, (or design circuit elements that perform the same task) but choose values that result in 1 - 2mA of load current at most when the supply is operating.

Kevin
 
#4
Thanks Kevin... yes i believe they are motor start caps. I have read ppl are using motor run not motor start caps in their amps. I really don't understand the difference but i just want to know if this cap is better than a regular electrolytic.
If it's not it would be stupid of me using it as it needs a lot of space.

I have removed the resistors.
Maximum voltage is ok....B+ will be 230 Volts.
 
#7
Motor run caps tend to be of very durable metal can polypropylene in oil construction, motor starts are usually electrolytic. I wouldnt put more than VAC RMS *1.4 = VDC on a motor start cap, but theres nothing wrong with them as electrolytics go. They are big because they are bipolar.

A motor run cap is usually good for VAC RMS *2 = VDC. Motor runs also have good sonic qualities and are suitable for use in crossovers etc.
 
#8
In AC (motor) application current flows in the cap. Motor start caps are designed to create a phase shift to start the motor. They handle large currents for a few seconds and then, no current. Some of these are indeed non polar electrolytic.

A motor run cap passes current continuously. They are made to handle this. To pass current without dissipating much power (most of the current is reactive) the ESR and DF are low. These are good qualities for audio use.
 
#9
Cap says MKP. Can this be an electrolytic?


They seem to work allright...no strange noises.

Thanks Tweeker and Tubelab, great info.


Tubelab i have to say this: you're a joy to read. Never too much, never too little; all to the point and well explained. I have learnt a lot reading your posts. Don't ever leave this forum.
😉
 
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