Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: LoudonMiller on September 26, 2025, 08:21:42 am
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Noob question.
I can't quite figure out the 47 ohm resistors (R35, R36) on the upper-right hand corner of the turret board.
https://el34world.com/Hoffman/files/Hoffman_Pro_Jr.pdf (https://el34world.com/Hoffman/files/Hoffman_Pro_Jr.pdf)
Are these two resistors part of the heater circuit which go to ground, connected between the pilot light and the heaters?
I thought these were the artificial center tap resistors (which could be wired to the fender lamp assembly or can be on the board), but I thought those resistors needed to be 100 ohm.
Ultimately, I'm both not sure what is connected to those 47 ohm resistors on the board (dead end, no notation on the pdf) and I'm not sure if I need to wire separate 100 ohm resistors to my lamp assembly. Something tells me that these two things are related and I'm just missing it...
Thanks in advance,
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It's smart to ask questions! You are correct that they are part of the heater circuit. If you look at the second page of thr layout you posted, you'll be able to see how they connect to the heater circuit.
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I think that value is just a carryover from what Fender used in the commercial Pro Jr circuit. I've seen anything from 22 ohm to 250 ohm per leg to ground or DC reference used for that purpose. I think any low value resistor pair of suitable power rating will work just fine.
Checkout Merlin's site (he frequents this board too) for a deeper dive. https://www.valvewizard.co.uk/heater.html
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Thanks, guys. I'm back to the project! Will post pics.