Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: bohema79 on January 29, 2014, 06:27:20 pm

Title: Vintage fender BF PR testing Blue Ajax caps
Post by: bohema79 on January 29, 2014, 06:27:20 pm

Hi Guys,
Is there a good way to test the two Blue Ajax .1 Pi tube coupling capacitors for leakage in a bf Fender PR?
I've tested the rest of the caps but these two give me some problemems because the negative voltage is on both ends.

Thank you for the help.

Title: Re: Vintage fender BF PR testing Blue Ajax caps
Post by: sluckey on January 29, 2014, 06:59:02 pm

Quote

Is there a good way to test the two Blue Ajax .1 Pi tube coupling capacitors for leakage in a bf Fender PR?
I've tested the rest of the caps but these two give me some problemems because the negative voltage is on both wides.

To test for leakage you need to lift the end of the cap that is NOT connected to the PI. Then connect your meter leads between chassis and the dangling end of the cap. The higher positive voltage you have, the higher leakage you have.

Title: Re: Vintage fender BF PR testing Blue Ajax caps
Post by: bohema79 on January 30, 2014, 07:07:39 am

Hi,
Thank you for the help.
I did as told and the caps seem to be fine!

Title: Re: Vintage fender BF PR testing Blue Ajax caps
Post by: 6G6 on January 30, 2014, 09:03:22 am

Those old blue ones usually are.  :icon_biggrin:

Title: Re: Vintage fender BF PR testing Blue Ajax caps
Post by: eleventeen on January 30, 2014, 12:08:23 pm

Those seem to stay working pretty well....I got perhaps a hundred of them out of an old CONN organ but unfortunately, 90% are 200 volt rated.

Title: Re: Vintage fender BF PR testing Blue Ajax caps
Post by: bohema79 on January 30, 2014, 03:42:07 pm

Guys, can someone please tell me what's the function of the .1 large "blob" capacitor and the other .02 ceramic disc next to it in the vintage Princeton Reverb?

Thanks!

Title: Re: Vintage fender BF PR testing Blue Ajax caps
Post by: sluckey on January 30, 2014, 04:02:55 pm

The .1 is a coupling cap between the LFO plate and the intensity pot. It passes the LFO signal but blocks dc voltage.

The .02 is just a small filter for the LFO signal.

Title: Re: Vintage fender BF PR testing Blue Ajax caps
Post by: bohema79 on January 30, 2014, 04:24:18 pm

Thank you sluckey!
Do these caps have any impact on the tone of the amp or is it just the tremolo?