Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dscottguitars on March 25, 2018, 06:23:16 pm

Title: Old coupling caps
Post by: dscottguitars on March 25, 2018, 06:23:16 pm

Hi, what's everyone's opinion about using old caps like these?

Title: Re: Old coupling caps
Post by: DummyLoad on March 25, 2018, 06:28:14 pm

used: circular file. NOS: test first.


--pete

Title: Re: Old coupling caps
Post by: sluckey on March 25, 2018, 07:27:28 pm

All of those caps would go in the trash can.

Title: Re: Old coupling caps
Post by: jjasilli on March 25, 2018, 08:32:35 pm

I'm a fan of of old plastic caps: Sprague, Pyramid, Sangamo, to name a few. I think they tend to retain their uF value, but you may as well just assume they leak DC.  So I do use them for guitar tone caps.  They could also be used in a tonestack assuming that a coupling cap is already blocking DC to the tonestack. 


Why use them?  It depends if you believe that different caps impart different one.

Title: Re: Old coupling caps
Post by: dscottguitars on March 25, 2018, 09:09:35 pm

Thanks for the responses. I am selling them on ebay.

Title: Re: Old coupling caps
Post by: terminalgs on March 26, 2018, 10:20:11 am

those bumble caps (in your pic, far right) are terrible for leaking DC.  i recently tested about 20 that I had clipped out of parts tape machines.   the test scenario was as a coupling cap with 100v on one side, and 470K resistor to ground on the other. maybe 2 or 3 didn't leak any DC,  the others leaked between 10V and 50V.


I have a 50's AM/FM Zenith radio that had one of those  serving death-cap duty.  I listened to the radio daily for 5-6 years.  One day came a loud pop! then smoke...  see below, the bumble bee exploded.


(https://i.imgur.com/NmYitmFl.jpg)




they are really just absolute junk if DC voltage will be on either side of them.

Title: Re: Old coupling caps
Post by: Platefire on March 27, 2018, 12:49:07 am

I would never use used caps. I have used NOS caps when to keep from making an order for one or two to finish a project. Too much work to risk a premature failure on a used cap. Platefire