Big ole power resistor question

[dynaman]

What's the absolute minimum power rating I can use for the big 1K 25W resistor found right after the diodes? Anyone know the formula?

Chris

[gearhead]

As per https://tubeamparchive.com/viewtopic.php?t=1313 thread, even a 10 watter gets hot.

From a pure DC standpoint, believe it's P=V*V/R which is (395-380)*(395-380)/1000, which gets you about 1/4 watt.

There must be a a big AC component, or I'm missing something.

[paulruby]

No less than 15W and with plenty of air-space around it. I used three 5W resistors in series to make it and stuck them on there own terminal strips for air space:

http://www.paulamps.com/MartaGuts.jpg

The problem is when playing, there is a lot of screen current drawn by the tubes, which ges through that resistor.

I initially had a 10W resistor mounted on the power supply board and it was way too hot when playing.

[Humbucker]

I used a 50 watt power resistor with metal casing. It was bolted to chassis to dissipate heat even more. However, I began to wonder: does the value affect the feel and sound? Should I change the power resistor to a smaller value? What do you say?

[paulruby]

The power handling of the resistor is not going to change the tone of the amp. 50W is overkill, but certainly not a problem.

[Humbucker]

Paul Ruby: Thank you. Well, we had no suitable lower value resistors at hand and 50-watters are kind of industry standard here.

[gearhead]

The problem is when playing, there is a lot of screen current drawn by the tubes, which ges through that resistor.

Does that then pull down the B+3 voltage?

[keithrick]

FYI - I got my power resistors from Apex Jr. 50w 1K ......$3 each.