Bypassing of PSU lytics with foils

[Tubetec]

In the motor shop I get to check all the caps with an LCR meter ,and have had the chance to measure brand new vs used specimens of the same type and manufacturer . Typically when a motor has been in use for a few years and returns to us ,I see a ten fold increase in ESR and some reduction in uf values maybe 10 % or more.  Even though its still works its always replaced , a bad start cap for instance wont provide proper torque when the motor is initially turned on and that causes a heavy current  on the run winding until the motor gets upto speed .

Foil run caps also see a reduction in value and an increase in ESR, typically though I imagine motor caps have a much tougher life than inside a tube amp , theres vibration heat and huge current pulses . A few years  in a motor seems to have a similar effect to maybe 20 years or more use in a tube based circuit

I think we live in different times now as far as extra mush and hash on the mains supply , its not just 50/60hz and its harmonics and any associated rectification effects , its switching psu garbage ,src dimmer buzz and other spikes ,which can very easliy endup making its way around  even regulated supplies and into audio circuitry . If not over the short term it does look like adding bypass caps could help more as your electrolytic starts to age .

 

[ruffrecords]

Correct.  For a modern electrolytic in radial format, the ESL is so low that impedance rise due to ESL is typically pushed out beyond 100kHz, and often to past 1MHz.  As such, one electrolytic cap presents a stable low impedance "voltage supply" to the local amp circuitry.  Ie. there is no need for any supplementary parallel cap for a normal audio amplifier.

But these days, 'past 1MHz' is an important area.

Cheers

Ian