Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: punkykatt on April 27, 2010, 12:15:56 pm

Title: How high is acceptable heater voltage for 5v rectifier tubes?
Post by: punkykatt on April 27, 2010, 12:15:56 pm

Hello  all, I have a Hammond power transformer that the 5v 3A  winding reads 6.2vac unloaded. I will be using a 5AR4 or a 5U4GB tube. Once the amp is built I will know the actual voltage. If I need to lower the voltage, can I install a resister in each each yellow heater wire going to the rectifier tube?  Thanks Punky

Title: Re: How high is acceptable heater voltage for 5v rectifier tubes?
Post by: FYL on April 27, 2010, 12:33:32 pm

Measure the windings resistance, calculate the reflected source R, then use Ohm's law.

Say the 5V winding shows a 0R5 source R, the PT will drop U = R * I = .5 * 2 = 1V using a GZ34. Your heater voltage will be 5.2V under load, nearly purrfect by any standards.

Title: Re: How high is acceptable heater voltage for 5v rectifier tubes?
Post by: punkykatt on April 27, 2010, 03:50:25 pm

Thanks FYL, for that great info.  Punky