Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Rustynuts on May 14, 2020, 09:40:05 pm

Title: What does this trimmer do ?
Post by: Rustynuts on May 14, 2020, 09:40:05 pm

Hi, I'm a newbie here and this is my first post.  If been gradually leaning about tube amps and have a few.  I have 4x el34  stereo amp.  This came from a church that had an old organ running into it.  ( No, it wasn't a B3 ) it hadn't been used for decades.  I replaced the valves and caps and added some 1/4" sockets.   It works great.  Tons of power.   I noticed this trimmer inside, not sure what it does.  Can someone enlighten me ? It's connected to the two sides of the heater filament circuit.   The orange wire goes to ground.   If I move it the heater voltage does not change. 

Title: Re: What does this trimmer do ?
Post by: DummyLoad on May 14, 2020, 10:24:23 pm

tapped resistor for filament hum reduction. adjust for minimum hum when idling with a speaker load, or with an oscilloscope, or AC voltmeter.


--pete

Title: Re: What does this trimmer do ?
Post by: vampwizzard on May 14, 2020, 10:30:54 pm

"Hum balance". Depending on the actual circuit there were a couple of ways they did this back in the day.

Title: Re: What does this trimmer do ?
Post by: nandrewjackson on May 15, 2020, 03:40:03 am

+1 for hum balance pot.




I like that amp ! 4 - EL34s !