29-07-2022, 08:43 PM
You know the Vidor 1957 FM Radio uses a DF97 triodised as an oscillator-self mixer on VHF as do all battery valve sets except early ones using a DC90.
The interesting thing on the Vidor is that on AM, that's a LO and the first FM IF (a DF97) is then the AM mixer, signal to g1 and LO to g2.
I'd not attempt a separate LO & Mixer at VHF. Almost ALL mains valve sets use the same idea of osc-mixer using a triode, or a triodised Pentode. Either EF80 or 1/2 ECC85 or part of ECF82. On a mains valve set the 1st EF80 or other RF stage is more to buffer the aerial so the roof top H or Yagi isn't radiating the LO. The Battery valve sets just have a whip, loop or two whips and a carefully tweaked balun between aerial and the DF97. Most transistor sets except for posh ones with HF, use s single transistor osc-mixer on VHF and a separate one for AM.
I'd only use the 1j37b for AGC at IF, or mixer at IF for BFO or for 10.7 MHz to 455 MHz on a dual conversion AM IF. I'd use the SAME triodised self oscillating mixer as every VHF radio. The only difference using the 1j24b or the 1j29b (not sure which would be better, but the ONLY two to consider) compared with an EF80 or the DF97 is the connection of g3, it goes to f- or f+ or 0V. The g2 connects to anode. I've tested swapping a DC90 and DF97 as VHF mixer/osc and only one connection needed cut on the Vidor valve base, which had no effect to the DF97 fitted.
I've tested the Vidor 1957 idea of a Pentode mixer at AM. Which was used on early 1930s superhets. It works driving the g2 of mixer from the anode of triodised osc direct. So 2x 1j24b can plug-in replace any battery valve heptode or Octode mixer osc (on those the g2 is really a sort of triode osc anode, g1 is feedback and some higher g number is RF in). The Pentode mixer on AM (like a Hexode with separate triode osc) has less LO leakage on the aerial than most heptodes or octodes.
I'm not saying you can't use a 1j37b as either FM mixer or 1st AM mixer, but it's going to be poorer (if it works at all on VHF) than the VHF mixer-osc triode or triodised pentode. Similarly on AM, the Pentode with RF to g1 and LO to G2 is how it's done. The 1j37b will be poorer and takes more filament.
The wunderlicht (sp) is an old 1930s dual grid triode that was used mainly as a detector, and sometimes as mixer. The 1j37b isn't quite the same, but it's better as IF DC controlled gain, a detector, frequency doubler or an IF frequency changer because the g1a and g1b need driven by a centre tapped transformer. Signal to centre tap and the drive is LO. For DC gain you feed RF or IF equally to g1a and g1b and differentially change the DC bias (you can fix either grid to 0V or f- and then you can use positive OR negative AGC volts. Max gain is DC of g1a and g1b are equal.
The 1j37b (and its cousins) don't at all work like a dual gain FET or the RF and LO grids on Hexode, Heptode, Octode and Nonode. Common mode signal on g1a and g1b is amplified. ANY differential signal (AC or DC), in any phase or polarity reduces the gain. So a rotten starting point to design a VHF front end. Use self osc mixer in triodised mode. It ought to be a little better than triodised EF 80 which barely reached 101 MHz. That's why the 108 MHz sets usually used ECC85 or occasionally ECF82.
The 1j37b was an interesting novelty looking for an application. It's only used as IF gain control or 2nd stage mixers or mixers for BFO on the Russian sets.
The interesting thing on the Vidor is that on AM, that's a LO and the first FM IF (a DF97) is then the AM mixer, signal to g1 and LO to g2.
I'd not attempt a separate LO & Mixer at VHF. Almost ALL mains valve sets use the same idea of osc-mixer using a triode, or a triodised Pentode. Either EF80 or 1/2 ECC85 or part of ECF82. On a mains valve set the 1st EF80 or other RF stage is more to buffer the aerial so the roof top H or Yagi isn't radiating the LO. The Battery valve sets just have a whip, loop or two whips and a carefully tweaked balun between aerial and the DF97. Most transistor sets except for posh ones with HF, use s single transistor osc-mixer on VHF and a separate one for AM.
I'd only use the 1j37b for AGC at IF, or mixer at IF for BFO or for 10.7 MHz to 455 MHz on a dual conversion AM IF. I'd use the SAME triodised self oscillating mixer as every VHF radio. The only difference using the 1j24b or the 1j29b (not sure which would be better, but the ONLY two to consider) compared with an EF80 or the DF97 is the connection of g3, it goes to f- or f+ or 0V. The g2 connects to anode. I've tested swapping a DC90 and DF97 as VHF mixer/osc and only one connection needed cut on the Vidor valve base, which had no effect to the DF97 fitted.
I've tested the Vidor 1957 idea of a Pentode mixer at AM. Which was used on early 1930s superhets. It works driving the g2 of mixer from the anode of triodised osc direct. So 2x 1j24b can plug-in replace any battery valve heptode or Octode mixer osc (on those the g2 is really a sort of triode osc anode, g1 is feedback and some higher g number is RF in). The Pentode mixer on AM (like a Hexode with separate triode osc) has less LO leakage on the aerial than most heptodes or octodes.
I'm not saying you can't use a 1j37b as either FM mixer or 1st AM mixer, but it's going to be poorer (if it works at all on VHF) than the VHF mixer-osc triode or triodised pentode. Similarly on AM, the Pentode with RF to g1 and LO to G2 is how it's done. The 1j37b will be poorer and takes more filament.
The wunderlicht (sp) is an old 1930s dual grid triode that was used mainly as a detector, and sometimes as mixer. The 1j37b isn't quite the same, but it's better as IF DC controlled gain, a detector, frequency doubler or an IF frequency changer because the g1a and g1b need driven by a centre tapped transformer. Signal to centre tap and the drive is LO. For DC gain you feed RF or IF equally to g1a and g1b and differentially change the DC bias (you can fix either grid to 0V or f- and then you can use positive OR negative AGC volts. Max gain is DC of g1a and g1b are equal.
The 1j37b (and its cousins) don't at all work like a dual gain FET or the RF and LO grids on Hexode, Heptode, Octode and Nonode. Common mode signal on g1a and g1b is amplified. ANY differential signal (AC or DC), in any phase or polarity reduces the gain. So a rotten starting point to design a VHF front end. Use self osc mixer in triodised mode. It ought to be a little better than triodised EF 80 which barely reached 101 MHz. That's why the 108 MHz sets usually used ECC85 or occasionally ECF82.
The 1j37b was an interesting novelty looking for an application. It's only used as IF gain control or 2nd stage mixers or mixers for BFO on the Russian sets.
