Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Big chief on February 21, 2021, 08:57:53 am

Title: Ampeg B 12 XT
Post by: Big chief on February 21, 2021, 08:57:53 am

Can some one please tell me where the out put wire for the reverb tank goes on the circuit board as I can not find on schematic  the wire has fallen off  any help would be great
Ampeg B12 XT
Thanks

Title: Re: Ampeg B 12 XT
Post by: sluckey on February 21, 2021, 09:26:13 am

Look at the top right of the schematic. It's called echo unit.

Title: Re: Ampeg B 12 XT
Post by: Big chief on February 24, 2021, 07:50:31 pm

Replaced the capacitors in this amp as per my friends request.
Have distortion on channel one channel two sounds great
All tubes check ok. Retintion all tube sockets and cleaned tube sockets
Voltages seem to be close to schematic on all tubes

Getting DC volts through some of the capacitors that my friend gave me to install
I do not know where to check from here  Could I have some bad caps? .047 .022

Please help

Title: Re: Ampeg B 12 XT
Post by: sluckey on February 24, 2021, 11:07:20 pm

Quote from: Big chief on February 24, 2021, 07:50:31 pm

Getting DC volts through some of the capacitors that my friend gave me to install
I do not know where to check from here  Could I have some bad caps? .047 .022

Good caps don't pass DC. However, once a cap is installed in a circuit you can't just say some caps pass DC. Some times there is supposed to be DC on both sides of the cap. I see several such cases on that schematic. To test for a leaky cap you must disconnect the end of the cap that's connected to the lower voltage then fire up the amp and check for voltage on the dangling end of the cap. If voltage is present, then the cap is leaky.

Title: Re: Ampeg B 12 XT
Post by: Big chief on February 25, 2021, 10:07:41 am

I can not figure out what I did wrong as I replaced each cap I at a time
very bad distortion only on channel one
I have attached photos a black mark is on caps that I have dc voltage on first cap on left 125 vdc
 next cap 295 vdc third cap 9.2

Title: Re: Ampeg B 12 XT
Post by: Big chief on February 25, 2021, 10:10:25 am

2nd photo

Title: Re: Ampeg B 12 XT
Post by: sluckey on February 25, 2021, 10:21:46 am

DID YOU READ MY REPLY?

Title: Re: Ampeg B 12 XT
Post by: Big chief on February 25, 2021, 11:07:38 am

Sorry I just read your reply will try now to check each cap
Thanks very much

Title: Re: Ampeg B 12 XT
Post by: Big chief on February 25, 2021, 03:37:51 pm

Checked capacitors none leaking any suggestions where I go from here?