• 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.

DC coupled 6P15P

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Hey Anyone,

I want to build a DC coupled amp. It would be a SE amp using a 6GK5 to drive a parallel pair of 6P15p outputs. (If this is even possible that is) The idea came from the fact that the 6GK5 runs well in the 135 to 150 volt range. Which is about the right voltage for 6P15P grid 2. My question is would applying 150 volts DC to grid 1 be possible? And if that can be done would it make it unnecessary to apply voltage to grid 2? Or would the DC have to be applied to both grid 1 & 2? I'm assuming there would need to be a grid stopper in place to limit current? I have all the parts to build this amp. And will only DC couple it if it would possible. Of course I could build it without the cap first, assuming it wouldn't damage the tubes. Any help would be much appreciated.

It is possible to apply 150V to g1 of a 6P15P. The valve probably won't survive such rough treatment, though. g1 and g2 are not the same thing so you can't swap their voltages around. I think you need to do some more reading about how pentodes work.

Some valves can have g2 drive. I don't know if that is one of them. In some cases (very beefy valves) a feed for g1 (via a resistor to limit current) can also be done. Generally this is only for valves designed for Class C or AB2, as they can cope with g1 grid current.
Thanks DF96,

So driving grid 2 with the AC input is possible? That thought had occurred to me. It would be simple enough to try. If it doesn't work I could just add a coupling cap to grid 1. I could also try DC coupled to grid 2 withAC coupling to gird 1? Or two inputs to the tube might really muck things up?

The thing about being an amateur is you don't know what won't work.


Thanks for the thread. Quoting Tubelab,
You want to look for the lowest maximum screen grid voltage rating that you can find. This implies good screen sensitivity.
Maximum screen grid voltage on 6P15p is 150 volts. I know from experience that 6P15P is verysensitive much more than EL84. Also, Anatoliy tells me that on 6P15P grid2 is denser than EL84. So it might just work. Its worth a try.

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I was thinking some thing like this?


  • 6GK5-6P15Pschematic-2.JPG
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