Troubleshooting magnavox 9302-00

[poolorpond]

Eight years ago, I shelved this amp (new wife, kid, house, etc). I had switched the power on and off a number of times for some reason and the rectifier tube went. One of the output transformers heated up to the point where the sound was distorting and it was dripping wax.

Jump to today- With a NOS sylvania 5u4gb rectifier, and the output transformers disconnected, no tubes in the sockets, the B+ is putting out 428 volts dc @ a stable .37 amps with 120vac feeding the primaries (brought up to power with a variac). There are 623vac across the secondaries before the regulator. The power supply caps tested accurate capacitance and no short on my DMM. There is a choke, too. Stock configuration- just like the schematic.

Even with no load, 428 vac seems high to me. I would only expect about 50v sag with that rectifier. Any thoughts on that .37 amps? Anyone have any experience with this amp/tranny?

Need some suggestions about what to test next. Should I reconnect the tubes and bring up the voltage, with the output transformers still disconnected (ready to hit the kill switch)?

 

[azazello]

Disconnect middle point of OT from +U and look at what about 0.37 amps.
Where You measure 0.37?

 

[poolorpond]

.37 amps drawn from a DMM in series with the primaries of the power transformer.

 

[poolorpond]

I never tested the power supply voltage. I have no idea what it might have been before my little accident. I have seen schematics of amps using el84 PP output stages with a B of 350v, which is well above the recommended plate voltage. I'm really not into over-driving a tube like that.

 

[dgta]

428V at .37A is over 150W. Find out where that current is going. That's a lot of power and something should be getting hot.

 

[poolorpond]

Nothing is hot. But i never touched the choke. I'll check it out tomorrow. I actually thought that it should have been drawing more, just to heat the filaments on the rectifier.

 

[dgta]

Your 5U4 draws [email protected] That's 15W, less than 10% of what you said you measured. Also make sure you are actually measuring .37A at 428V.

 

[azazello]

Disconnect all secondaries and measure with DMM primary. Then connect heater coils and measure primary. Then connect rect. tube without wire to first el. cap. Note, if You connect only PS elements, +U can be more 400 V /without load/, that is dangerous and death U. If You never measure high voltages, better don't do that! When output stages are connected +U can be about 350 V. Then connect middle points of OTs. Every time switch off if You something connect and then switch on and measure!