Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: silat on September 10, 2016, 08:42:16 am

Title: 59 Bassman Clone doing weird things.
Post by: silat on September 10, 2016, 08:42:16 am

Hello all, So I went to put an adjustable bias into my son's Tweed Bassman and I noticed it was not playing when I turned it on. It  had some bad tubes  in the preamp portion.  I changed the tubes and still not playing. Anyhow I pulled all the tubes and then put 50k linear pot in for the adjustable bias and adjusted it to about 44.7.  I happened to touch the phase inverter 470 ohm resister which goes to the cathode and the amp played loud and strong. I thought maybe there was a bad solder joint so I re-soldered it and nothing. I touched the probe and it played but when I turned the meter off it stopped playing. Does anyone have an idea why r what is causing this? :BangHead:

Thanks!
 Silat

Title: Re: 59 Bassman Clone doing weird things.
Post by: shooter on September 10, 2016, 09:21:03 am

Quote

I touched the probe and it played

Suspect the meter is completing an open circuit. with power off n discharged ohm the PI's cathode to ground

Title: Re: 59 Bassman Clone doing weird things.
Post by: silat on September 10, 2016, 09:30:58 am

Thank you Shooter, that must be it. I am dumbfounded how that could have happened just sitting and not being played much by my son.