Reasons for tonal changes as amp warms up

[Alan0354]

You sure 36mA per tube is high enough? I would increase a little to see whether the sound gets better.

[Mick Bailey]

My immediate thought was to suspect the PI circuit. Check the PI voltages cold and when the problem occurs. A hairdryer should warm things up a little to accelerate the fault.

Another possibility is a screen resistor playing up. Measure the voltage across each when cold/hot.

[kg]

speaker coils heat up too, you know.

higher t means higher dcr means higher q.

[daz]

My immediate thought was to suspect the PI circuit. Check the PI voltages cold and when the problem occurs. A hairdryer should warm things up a little to accelerate the fault.

Another possibility is a screen resistor playing up. Measure the voltage across each when cold/hot.

I was thinking about that myself. Today i'm cleaning up the sloppiness and when i tray it tonite i'll write down all the voltages then let it get hot and see how it does. My only problem is it doesn't seem like that fan could have stopped the issue as fast as it did if it were a component. But if the bias isn't hot i guess it can't be a tube especially considering they all got swapped. Anyways, i'll do that tonite. When i get it right i gotta try and stop screwing with this thing ! Of course thats wishful thinking...

[Mick Bailey]

What's your B+? Bias could be fine.

Your heater voltage isn't anything to worry about - plenty of amps run heaters at 7.something - particularly Fenders made in the last 20 years.

[daz]

What's your B+? Bias could be fine.

Your heater voltage isn't anything to worry about - plenty of amps run heaters at 7.something - particularly Fenders made in the last 20 years.

440v