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In Reply to: RE: What to do with 490V??? posted by Paul Joppa on November 22, 2015 at 14:37:08
The KT88 was to be triode/UL switchable with a 24v zener drop to the screens in UL.
I figured the fast warmup of a 5r4 would create a V spike before the KTs warmed up. I'm using a 370Vac motor run cap paralled with 370V film snubber cap (total around 80uf). I was counting on the slow turn on of a 5ar4 to prevent the spike (which could go to 700 V). Though the caps may take the spike, the driver tubes might curse at me and quit.
Follow Ups:
With that much dcr it will end up dam close to 400vdc...with 150ma draw. Mock it up with clip leads and find out man! JH
You can use the PSUD code to simulate the power supply; it will give you a good estimate of the voltage and allows various tube rectifiers.
If you need to operate at different voltages than your circuit was developed for, then some design changes will be needed to get the best performance. These things can be calculated; here is one example:
In triode mode, running higher voltage would call for reduced current if you want to retain the plate dissipation. Both of those changes call for a higher impedance output transformer. Ultralinear also calls for a higher impedance transformer than triode, if you want to take full advantage.
You can use a 555 timer circuit with a relay to delay the filament voltage to the rectifier tube to ensure the rest of the tubes are ready to conduct when the B+ comes up. I have used this approach and it works well for me.
"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln
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