6MN8 connected as one triode

[geezertron]

Finally getting back to tube stuff after moving to a new house....

I found a bunch of 'MN8 tubes I bought cheap (see attached specs) without realizing that the cathode were connected together internally.

Can I just connect the grids and the plates together and make a 9W triode out of it?

Thanks...

 

[Miles Prower]

Yes you can. Since this is a highish gain triode, I would include individual stopper resistors for each grid, as opposed to no stopper, or one for paralleled grids.

 

[MrCurwen]

Or, you could use them separately as fixed grid bias stages.

If you use two of them, you have 6 gain stages! You could build a multi channel amp for surround sound movies...

 

[Tubelab_com]

I'm sure that the technically correct answer is, no, one of the sections will have a higher Gm and therefore hog more than it's share of current. It will probably make no difference unless you intend to use all 9 watts, or maybe more.

Having said that I have several 6MD8's. Also a triple triode compactron tube with a shared cathode, but with a Mu of 17.

I had the same thought, along with my usual "how much power can I squeeze out of these" thoughts. I wired all 3 sections in parallel and cranked a pair of them up in a push pull amp. I thought.....super 6SN7, but 6SN7's are too useful to purposefully torture.

I could squeeze about 20 watts from the pair. I used a 6600 ohm OPT and just turned the bias and plate voltage knobs for max power. No attempt was made to optimize the load impedance.

In every case the middle triode was the one that red plated first. This led me to the conclusion that current hogging is less of a problem than heat radiation from the middle triode.

I don't remember the point of glow, but I believe it was considerably above 9 watts. This all happened several years ago. The fact that I still have the tubes tells me that I though that they were good for something.

 

[jazbo8]

I don't remember the point of glow, but I believe it was considerably above 9 watts.

So dial it down a bit until the redness disappears for improved reliability, I have got some on hand, might be worth a try. Another app might be mixer/CF to drive a tone stack for example.