using 4-125 as triode connected modulator

[w4bfs]

I am curious to know if this can be done in similar fashion as 6AQ5 thru 803/813.  I have looked thru my handbooks with nary a hit.

[K1JJ]

John,


I have not heard of 4-125's used triode-connected in audio modulator service yet, but they should work just fine in that config.

I'm a big fan of triode-connecting certain tetrodes because of the simplicity and excellent results.

My thinking is that the 4-1000A works superbly well triode-connected. The 4-400 does too. The 4-250 / 4-125 are just little brothers of these two bigger tubes, so should work well also.

Even the 813, being a much different tube, does a wonderful, clean job when triode connected.

This should help until someone chimes in with actual experience using them.

If you try it, let us know how it works out.

T

[John K5PRO]

As long as you don't exceed the grid or screen dissipation, (V x I) triode connected tetrodes are OK. There have been warnings from Eimac and Bill Orr literature somewhere, about this. I think it is more tricky when you bias the grids with proper voltage, AND ground them for RF service, and try to operate cathode driven mode. This shouldn't be problem with audio, as the gain is back down to what a triode would be (or worse). Maybe it was one of the old Eimac Ham app notes?