14-06-2020, 11:13 AM
(This post was last modified: 14-06-2020, 11:14 AM by Mike Watterson.)
Joe has done brilliant work.
There may be millions of some of the commonly used rod "pentodes". All military production and the factories had fixed annual quotas till the end of the of the USSR. No unemployment, in theory. So officials wouldn't cut back the quotas, because that would mean redeploying workers to the Gulags. The system was after all run by humans. A lot of stock would have been in Ukraine because they made a lot of the USSR aircraft. Not sure why there are lots in Bulgaria.
Don't forget to not just decouple g2, but use either a tapped supply or a potential divider. The gain varies so much with g2, that you can use it for AGC or DC control of power out, for 90V HT, the 1j24b uses about 20V to 50V for almost no gain to full gain. The voltage range varies with nominal anode bias and model of rod valve. I've actually one US radio where the "RF Gain" pot actually varies the HT on g2 of the two IF amps, the 1T4 (DF91). You can use the deflector pin drive of a magic eye to derive such high level positive going AGC from the normal negative detector.
Also you can vary RF or AF power out on any amp, class AB or class A or possibly class C using any of the rod tubes and a suitable voltage on g2.
The g2 is also a good input for a local oscillator to modulate. The only regular battery set I know doing that is the Vidor AM/FM model using a DF97 as 1st FM IF, but as mixer on AM. It uses a triodised DF97 as self mixer/oscillator on VHF (all the rod tubes can do that) and LO only on MW and LW. It's a good template to use to make a complete Rod Tube AM/FM radio, you just need to change the g2 resistors to potential dividers with a second resistor. All the same values will work. The DAF96 can be replaced with 1j24b and an 1N60 (1st released in 1946) and the FM detector in all battery valve radios is 2 x diodes like 1N60 anyway.
You can use all 1j24b, or do the push pull audio out (then a 110-0-110 mains transformer can be used) with 1j24b, 1j29b or 1p24b, with option to have economy mode on the 1j29b or 1p24b by turning off half the filament. You can design for 2.4V nominal LT, more series than that is difficult. With it being push pull, you use the valves in parallel filament and adjust the bias for the valve that's more positive. You need to DC filter the local oscillator for -ve bias as per the Philips Colette, as the trick of series resistor between LT- and HT- loses too much HT at Class AB. The 1j29b may need a PP3 or 3 x lithium coin cells for Class AB bias and the 1p24b may need more negative g1 bias if you go for 120V to 150V HT for serious audio power. You'd want AA cells for the HT, with a fuse, for more than 300mW audio!
There may be millions of some of the commonly used rod "pentodes". All military production and the factories had fixed annual quotas till the end of the of the USSR. No unemployment, in theory. So officials wouldn't cut back the quotas, because that would mean redeploying workers to the Gulags. The system was after all run by humans. A lot of stock would have been in Ukraine because they made a lot of the USSR aircraft. Not sure why there are lots in Bulgaria.
Don't forget to not just decouple g2, but use either a tapped supply or a potential divider. The gain varies so much with g2, that you can use it for AGC or DC control of power out, for 90V HT, the 1j24b uses about 20V to 50V for almost no gain to full gain. The voltage range varies with nominal anode bias and model of rod valve. I've actually one US radio where the "RF Gain" pot actually varies the HT on g2 of the two IF amps, the 1T4 (DF91). You can use the deflector pin drive of a magic eye to derive such high level positive going AGC from the normal negative detector.
Also you can vary RF or AF power out on any amp, class AB or class A or possibly class C using any of the rod tubes and a suitable voltage on g2.
The g2 is also a good input for a local oscillator to modulate. The only regular battery set I know doing that is the Vidor AM/FM model using a DF97 as 1st FM IF, but as mixer on AM. It uses a triodised DF97 as self mixer/oscillator on VHF (all the rod tubes can do that) and LO only on MW and LW. It's a good template to use to make a complete Rod Tube AM/FM radio, you just need to change the g2 resistors to potential dividers with a second resistor. All the same values will work. The DAF96 can be replaced with 1j24b and an 1N60 (1st released in 1946) and the FM detector in all battery valve radios is 2 x diodes like 1N60 anyway.
You can use all 1j24b, or do the push pull audio out (then a 110-0-110 mains transformer can be used) with 1j24b, 1j29b or 1p24b, with option to have economy mode on the 1j29b or 1p24b by turning off half the filament. You can design for 2.4V nominal LT, more series than that is difficult. With it being push pull, you use the valves in parallel filament and adjust the bias for the valve that's more positive. You need to DC filter the local oscillator for -ve bias as per the Philips Colette, as the trick of series resistor between LT- and HT- loses too much HT at Class AB. The 1j29b may need a PP3 or 3 x lithium coin cells for Class AB bias and the 1p24b may need more negative g1 bias if you go for 120V to 150V HT for serious audio power. You'd want AA cells for the HT, with a fuse, for more than 300mW audio!
