14-04-2021, 01:03 PM
(This post was last modified: 14-04-2021, 01:09 PM by Mike Watterson.)
The Russian radios using rod pentodes used the 1j37b for AGC/AVC, because inherently you've only got some gain control via Vg2 and it's not great for very big signals. They did also experiment with Vg3.
The Vg2 does work reasonably, nearly as good as a DK92 mixer, for LO injection to make a mixer. One Vidor model in 1950s uses a DF97 this way for MW & LW mixer, which is a 1st IF on FM. On FM a DF97 is a mixer osc as on German sets or the EF80 on FM. On AM, that valve is the LO only.
Both grids together for signal on 1j37b. Differential voltage on the pair of g1 varies the gain very like variable mu. See Radio museum article. Naturally that also works as a mixer if one signal is the LO and one is RF, then AGC can also be added.
The 1j42a should allow something similar, but it has lower Ra and a very low max Va. Also rarer.
Another alternative is 4 x matched 1N34 or similar as they pre-date rod pentodes as ring diode mixer. Copper Oxide was used in the 1930s for SSB mixers on telephone trunks.
The Vg2 does work reasonably, nearly as good as a DK92 mixer, for LO injection to make a mixer. One Vidor model in 1950s uses a DF97 this way for MW & LW mixer, which is a 1st IF on FM. On FM a DF97 is a mixer osc as on German sets or the EF80 on FM. On AM, that valve is the LO only.
Both grids together for signal on 1j37b. Differential voltage on the pair of g1 varies the gain very like variable mu. See Radio museum article. Naturally that also works as a mixer if one signal is the LO and one is RF, then AGC can also be added.
The 1j42a should allow something similar, but it has lower Ra and a very low max Va. Also rarer.
Another alternative is 4 x matched 1N34 or similar as they pre-date rod pentodes as ring diode mixer. Copper Oxide was used in the 1930s for SSB mixers on telephone trunks.
