660 volts on the plates?!

[Axtman]

I am working on a Univox 1221 amplifier. This amp uses two 6L6GC tube and claims to get 100 watts (snicker). The schematic show the plates getting a whopping 660 volts!

I think the voltages shown on the schematic are based on the Japan's 100 volts. I guess they figured 110 USA volts wouldn't effect much since it's only 10% more. Well my outlet voltage is 123 volts and the reading I get on the plates is 739 volts!

I can't imagine any modern 6L6GC tube lasting very long at these voltages. I am still stumped why they would use a voltage doubler in the power supply. 320 volts would be sufficient.

[TomCarlos]

I could not open your pdf.

http://www.prowessamplifiers.com/sch...ivox/1221.html

[TomCarlos]

Axtman:

Take a look at this thread - https://music-electronics-forum.com/...ad.php?t=32478

[Enzo]

COnsidering the PT has both 100v and 115v taps, I tend to doubt they thought a 100v amp would be OK on 115v as is.

They were trying to extract maximum power. Note the screens are running at half the B+.

Unless they are arcing over inside, I worry more about dissipation than voltage.

[TomCarlos]

I just checked the Tube Bias Calculator at Robrobinette.com.

For 660V on a 6L6GW (30 watt tube), the results are as follows for Class AB:

50% Cool = 22.7 milliamp
60% Average = 27.3 milliamp
70% Max Safe Dissipation = 31.8 milliamp

Does that sound right?

[g1]

If you consider 50% cool.
At that kind of plate voltage I consider MusicMan cool at somewhere around 12%.

[Enzo]

The Robinette feature just looks at those three percentages in those terms. It just figures 50,60, and 70% and calls them that. To them, 50% is cool regardless.

[Helmholtz]

320 volts would be sufficient.

...but only for an output of around 25W per pair.

[Jazz P Bass]

I had one of these beasts come through.
720Vdc.
I installed Sovtek WXT's.
Biased to 20%.

[Helmholtz]

Biased to 20%.

Based on disappearing crossover notch?

Just out of curiosity, what was output power?

[Jazz P Bass]

Based on disappearing crossover notch?

Just out of curiosity, what was output power?

Yep.
I do not recall the output power.
Certainly not 100 watts.