24-10-2023, 01:11 PM
(This post was last modified: 24-10-2023, 01:15 PM by Mike Watterson.)
Yes, g3 can be used as mixer input. I was quoting translation of USSR recommendations.
I found that more modulation depth is possible with g2 (for AM transmitter), but of course that has a large voltage offset and needs up to 10v pk-pk drive. I mean to try using the DM70 or similar as AGC amp & offset to drive g2. Also g2 mixing works well connected direct to a triodised anode that's the oscillator.
There doesn't seem to be any taper on the construction and of course the valves used for effective AGC on g1 have a progressively wider spiral on g1, which also makes those worse as an RF front end. There will be less IM using a sharp cut-off valve and gain via g2, which Hallicrafters do on some battery valve sets. Some of the USSR sets extravagantly used 1j37b just as a variable gain block rather than varying g2. They seemed to always ground g3 and in earlier types it's tied to the filament.
Some models have the screen rods to a separate pin and that could be investigated for modulation.
The other advantage of say 0.9V to 1.15V filament is dramatically longer life compared to 1.25V to 1.35V. Unlike the 1.4V B7G valves they do work well at 0.9V.
I found that more modulation depth is possible with g2 (for AM transmitter), but of course that has a large voltage offset and needs up to 10v pk-pk drive. I mean to try using the DM70 or similar as AGC amp & offset to drive g2. Also g2 mixing works well connected direct to a triodised anode that's the oscillator.
There doesn't seem to be any taper on the construction and of course the valves used for effective AGC on g1 have a progressively wider spiral on g1, which also makes those worse as an RF front end. There will be less IM using a sharp cut-off valve and gain via g2, which Hallicrafters do on some battery valve sets. Some of the USSR sets extravagantly used 1j37b just as a variable gain block rather than varying g2. They seemed to always ground g3 and in earlier types it's tied to the filament.
Some models have the screen rods to a separate pin and that could be investigated for modulation.
The other advantage of say 0.9V to 1.15V filament is dramatically longer life compared to 1.25V to 1.35V. Unlike the 1.4V B7G valves they do work well at 0.9V.
