Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Kitarist on July 05, 2016, 10:31:29 pm

Title: Marshall Plexi 1987 Hum and Chirping Noise problem every since changed the PT
Post by: Kitarist on July 05, 2016, 10:31:29 pm

So the PT on this amp blew and i changed it with a new one. While the amp works and plays there are 2 types of noises coming from the amp.

The first one is coming from amp like a buzz hum noise while second noise is actually coming inside the amp its a weird chirping noise.

I'm not sure what could it be. I'm suspecting some filter caps got damaged but i'll  replace that also and keep you updated.

I alredy changed the rectifier dioes,tubes.

I was also suspecting the larmar PPIMV i changed the amp to stock and the problem was still present.

Here is also a video i made if anyone cares to take a look at it :)

Title: Re: Marshall Plexi 1987 Hum and Chirping Noise problem every since changed the OT
Post by: sluckey on July 05, 2016, 11:14:52 pm

Reverse the OT plate leads. Does that help?

Title: Re: Marshall Plexi 1987 Hum and Chirping Noise problem every since changed the PT
Post by: Kitarist on July 05, 2016, 11:47:46 pm

Sorry it was the PT made a typo ;)

I already checked heater polarity and so on...

Title: Re: Marshall Plexi 1987 Hum and Chirping Noise problem every since changed the PT
Post by: hesamadman on July 06, 2016, 11:12:39 am

That chirping sounds more like arcing. Does the new PT have a center tap for the the 6.3vac?