heaters poop out but work again after amp is off for a while.

[pullshocks]

The transformers in my quasi Dumble were re-purposed from an Eico Stereo amp.  The PT has 2 separate sets of heater taps (stereo amp, right?).  I used one set for the power amp and one set for the preamp.  After playing for maybe 30 minutes, there is a loss of sound.  The power amp heaters were still glowing.  The preamp tubes were dark.
Turned the amp on again later, and the preamp heaters heated right up.

Looking inside the amp, there is an obvious problem--I never soldered the heater wires to the pilot light.  They are crimped on snugly, but not soldered.  Since the pilot stayed lit, that connection has to be the problem, but  I don't understand why the problem would manifest itself after playing, and disappear when the amp is turned off for a while.  Any theories??

[kagliostro]

Any theories??

Your preamp have an heater consumption near the max admitted consumption of your PT Heater current (I doubt about that) and there is a form of thermal protection inside the transformer or there is a thermal protection that acts too quickly because damaged in some way

this is only a theory

---

have you try to swap the heater circuit of the preamp with the circuit of the power amp ?

have you measured the heater voltage of the two circuits without load, under load when all is fine and under load when the problem appears ?

Kagliostro

[stratele52]

Maybe with the heat build up connexion/ contact make change ?

To know if your power transformer can handle your heater load mesure with AC voltmeter the heater. You should have 6.3 volt AC, less than 6 volts your power transformer is not powerfull enough on this heater winding.

[PRR]

> I never soldered the heater wires ... crimped on snugly, but not soldered.

So solder them already!

> I don't understand why the problem would manifest itself after ...

Why ask why?

OK. I got a 300-Watt amplifier which had been in all-day service for years and then caught fire. In the autopsy I found a power-tube screen wire was crimped but never soldered. It drove film-projector motors in one of NYC's largest film-video transfer services for years before it let go.

Your crimp loosens when hot and so-far grips when cold. If you must study it, try a shot of freon on the crimp when it has just let-go. Or try a teeny heat-gun before you turn-on.

[stratele52]

Looking inside the amp, there is an obvious problem--I never soldered the heater wires to the pilot light.  They are crimped on snugly, but not soldered.   ?

I did not see that on my first reading ; Thank's PRR to weak up me.

Solder already