Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: apolloamps on May 31, 2012, 02:18:20 pm

Title: 900+ Volts on pin 3 using a NOS Hoffman 50 OT
Post by: apolloamps on May 31, 2012, 02:18:20 pm

Just finished an amp and I'm getting 900+ volts on the plates (yet the tubes don't glow red or white hot)(and the voltmeter works fine) . I think Hoffmans Tranny is fried or hooked up wrong. Never had this problem. The rest of the amp checks out perfect. What gives?
Hep me please
Thanks
 Steve

Title: Re: 900+ Volts on pin 3 using a NOS Hoffman 50 OT
Post by: Willabe on May 31, 2012, 02:28:46 pm

What color wires go where?

Can you post a drawing of how it's wired?

Title: Re: 900+ Volts on pin 3 using a NOS Hoffman 50 OT
Post by: stratele52 on May 31, 2012, 03:14:42 pm

900 volts each side probably, but if you mesure from ground ( there is a center tap in the middle of 900 volts winding ) , you must have 450 volts.

Title: Re: 900+ Volts on pin 3 using a NOS Hoffman 50 OT
Post by: plexi50 on May 31, 2012, 03:17:33 pm

Man thats dangerous. I would make certain your Power Transformer CT is grounded. Do you have a pic of your amps PT wiring?

Title: Re: 900+ Volts on pin 3 using a NOS Hoffman 50 OT
Post by: sluckey on May 31, 2012, 03:18:03 pm

Which amp? Is this a new build? What voltage do you measure on pin 4 of the output tube(s)? If you pull the PI tube does the voltage on pin 3 look more normal?

Title: Re: 900+ Volts on pin 3 using a NOS Hoffman 50 OT
Post by: navdave on May 31, 2012, 05:06:05 pm

Sounds like he hook up the PT in full wave bridged rectifier mode instead of full wave.