• 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.

'Real world' max plate voltages for 6DJ8, 6P15P?

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Hoping someone with experience with these toobz can help me out.

Can 6DJ8 work with 140V plate-cathode? Or is that too much?
(Sylvania 6DJ8 data sheet says max Va is 130V. My anticipated Pdiss is 0.9W, or Va of 140V, Ia of 6.5mA.)

Can triode wired 6P15P, using 1k resistor screen-plate, work with 290V plate-cathode?
(Russian data sheet shows max Va is 330V, max Vg2 is 330V, but max Pg2 is 1.5W, so only 4.5mA permissible Ig2 at that high a voltage.)

I know I'm pushing it in both cases, but... it would be nice if they did work OK.

^i will be more concerned about plate dissipation,
the datasheets are guides that when respected can ensure reasonable tube life...

pentodes when triode wired can usually take more voltage than G2 ratings imply,
tubelab has demonstrated this in many tubes he tortured...
The weak spot in the 6П15П (6p15p), AKA SV83, is the screen grid. If you are going to triode wire the type, tie g2 to the plate with a 1 Kohm resistor. If you are going to employ full pentode mode, regulate g2 B+ with an 0A2 or 0D3. UL mode is not feasible, unless you use custom, tertiary winding, O/P "iron", which permits the use of regulated g2 B+.
I doubt that ANY 12 watt dissipation pentode (6П15П) is going to have a problem with being run 10% overvoltage at its plate so long as its plate maximum sustained dissipation isn't exceeded. And who knows, even if it is, most tubes are definitely built to handle a little out-of-spec overdriving. They're durable and that is why we like 'em.

And moreover, any tube that bills itself as a 130 V plate max, 0.9 W tube is going to be just fine with even 25% over voltage and just as much over-power at the plate. I wouldn't design over-dissipation (power), but I wouldn't flinch at over-voltage because the voltages are so low. Remember that even Nuvistors (6CW4 for instance) had maximum plate ratings of 135 V, as design spec, and in practice could take up to 100% more than that as peak voltage as long as plate dissipation didn't get out of control.

Just saying
PS: and also remember it is SO EASY to drop a 0.9 ma power supply to plate by 10 volts. Just use a 11 kΩ series resistor and a bypass capacitor (at the plate side!) Or if you want it more modern-faddish, then a 10 volt zener diode. Does the job, never quits. Only has to dissipate 9 milliwatts. Either or.

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