Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dude on May 08, 2015, 11:05:41 am

Title: Leaking .02 cap ?
Post by: dude on May 08, 2015, 11:05:41 am

Is a .02 coupling cap in the tremolo circuit considered leaking if .01/.009 vdc are passing through it, testing with a 9 volt battery? Trying to fix a vibro in my VC.

al

Title: Re: Leaking .02 cap ?
Post by: shooter on May 08, 2015, 01:39:34 pm

try the same test with "close value" caps you have in your "drawer", if they all check the same as the test one, then you'll know.......maybe :icon_biggrin:

Ideally you shouldn't have DC getting through, but .01vdc might be *meter error*

Title: Re: Leaking .02 cap ?
Post by: dude on May 08, 2015, 04:39:56 pm

Quote from: shooter on May 08, 2015, 01:39:34 pm

try the same test with "close value" caps you have in your "drawer", if they all check the same as the test one, then you'll know.......maybe :icon_biggrin:

Ideally you shouldn't have DC getting through, but .01vdc might be *meter error*

Thanks, some of my drawer stock (new caps) also read .009, not all but I don't have any ceramic disc caps in the sizes needed for the tremolo in the Champ. Anyway I found an old tread here on fixing the vibrato, said basically in a Vibro Champ just just replace the e cap and check the resistors around that tube, I did and now it works. I checked all the R and caps, several had drifted a lot.
   
The amp plays Ok, but the bass is a little funky sounding and not much change from 1 to10 and the volume up, has a ratty distortion, low volume - nice and chimney.

Only thing left is filter cap can, I was thinking no hum it's ok but it's almost 40 years old. I think the cap can is trash, when I shut off the amp the voltage on the can drops too fast, like in 20 seconds it's 12vdc. It isn't holding higher current for any length of time. I think I'll leave it in for vintage looks but put three separate filters inside, I'll also be able to ground the preamp filter down near the input with separate caps.

I think I'll ground the filaments on the cathode of the power tube that should make this thing quite, any problem in running the filaments CT to the power tube cathode pin 8, it's a bout 20vdc?

al

Title: Re: Leaking .02 cap ?
Post by: shooter on May 08, 2015, 05:59:24 pm

Quote

any problem in running the filaments CT to the power tube cathode pin 8, it's a bout 20vdc?

Nope, Tubes do have a Cathode to heater rating, usually something like 100v cathode to heater.