'High mu' Triode connected pentodes

[BobWeaver]

Does anyone here have experience with triode connected pentodes using the so-called 'high-mu' triode connection? I got that term from Radio Engineering by F. Terman, who listed the 'medium mu' connection which we are more familiar with, where the screen is connected to the plate. But he also listed a high-mu connection where the screen is connected to the control grid. Just wondering if anyone has done anything with this connection.

[Nick]

No, but should be easy to see what the result is using the uTracer. What pentode did you have in mind?

[BobWeaver]

I don't have any specific pentode in mind at the moment, but had been thinking of television horizontal output valves, many of which are not particularly good for audio when used as a pentode, but might show some promise when triode connected.

However, I'd be interested in any valve with reasonable power rating if someone has a curve tracer and is willing to experiment. I'm curious about how much difference there is in mu between the so-called medium-mu and high-mu connections.

I did a quick experiment a few weeks ago using a low power pentode (6AU6 I think), and I couldn't get anything out of it at all in the high-mu connection.

[Nick]

Well, I could try it with something like a Ef86.

[Andrew]

If this works on EF86 I can bring some more pentodes down next time I see Nick and his uTracer.

Andrew

[BobWeaver]

The EF86 would likely be fine for testing the concept. It conveniently has the suppressor brought out to a separate pin. So, the effect of connecting it to the plate, other grids or cathode could also be investigated. Ultimately though, my interest would be in power valves.

I have a curve tracer project in the works. I breadboarded it a few months ago, and then disassembled it with the intention of putting it into a permanent enclosure. But I haven't got that far yet. I guess this may be a good excuse to move it up to the top of the priority list.