Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: ALK2MT on September 28, 2026, 09:37:58 pm

Title: GA5 Build Question - 6.3V to 5.0V Dropping Circuit
Post by: ALK2MT on September 28, 2026, 09:37:58 pm

Hi there. I’m working through the last few circuit checks before putting tubes in a GA5 scratch build and have a question/observation. In the circuit I am using a 5Y3 tube in V3 and an Antek AS-05T320 toroidal power transformer with 2 separate 6.3VAC supplies. I built a voltage dropping resistor circuit that is connected in series on the blue/green secondary 6.3V supply to drop 1.3V and safely provide 5.0 V to V3-2,8.

I used two 0.34 Ohm 10 Watt wirewound resistors, wired in series for a total of 0.68 Ohms. My tests show it is performing at spec 0.68Ohms. The voltage however is showing 6.7V at V3-2,8. So there has not been a voltage drop through the resistors.

Ideas? Thoughts? Coaching?

Thank you.

Title: Re: GA5 Build Question - 6.3V to 5.0V Dropping Circuit
Post by: roarshock on September 28, 2026, 09:57:25 pm

I'm no wizard, but if the resistors aren't dropping I gotta ask, were the tubes in the circuit? There won't be voltage drop if there's nothing drawing.

Title: Re: GA5 Build Question - 6.3V to 5.0V Dropping Circuit
Post by: Kaptinkangaru on September 28, 2026, 10:16:48 pm

Are you testing under load?

Title: Re: GA5 Build Question - 6.3V to 5.0V Dropping Circuit
Post by: ALK2MT on September 28, 2026, 10:19:48 pm

Tube in, 5.01Volts. Works great!