• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.


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hi!, got a question about heating...

my amp has a delay before switching HV (relais at transformer HV AC taps)

i use py500A set up as full-wave rectifier (4xpy500a)
Lately someone suggested me to put the relais at the filaments of the py500A so there would always be a slow startup...he said this would be better for tube-life than slamming the HV at the warm tubes.........

I was real happy with it and it looked real cool to see the diodes startup by themselves....so i told the tube man at work about it....

He said i was molesting my diode-tubes with this because they aren't hot yet while the amplifying tubes are...thus stripping the diodes cathode because they have to deliver current while cold.....

which is worse????

-slamming hot tubes with HV(seen mostly in amps)
-starting hot tubes with cold diodes

Is the solution maybe to just place the relais at the primary of the mains transformer?? then all tubes will be cold and it will be starting like an old radio......?

then i'll have to connect the PS of the diodes also behind this relay and recalculate the fuse size so i can power up with one button (diode bridge has it's own switch now)
Joined 2003
Your tube man is correct. However, what is the price of a PY500A compared to the audio valves? It depends on how fragile your audio valves are. For example, 6528 specifically warns against applying HT until the heater has been on for 45s. If you remove your relay, the (indirectly heated) PY500A will warm up at about the same speed as the audio valves (unless they're directly heated). The only (slight) danger to that is that some voltages may momentarily exceed their normal values - make sure your HT capacitors and coupling capacitors can withstand it. Without knowing your specific circuit, it's hard to comment, but removing the relay is probably fine.
I wouldn't like to overload my caps, 450v types (philips LL)
(why does that happen??? cathodes can't emit yet.....)

So i'll stick with heating all tubes and the after a minute the Relais will switch the HV

Best would be to heat all tubes and then after a minute gradually rise the HV, are there schematics for that??? if anyone has them ?!?!?!? thanx!!

i have attached a schematic of my amp.....

@tubes4e4: thnx for the idea....they're now just parrallel heated.....might also reduce the flashing somewhat....


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