29-06-2020, 08:53 AM
(This post was last modified: 29-06-2020, 08:57 AM by Murphyv310.)
Hi.
I attach a quick drawing of the circuit, there's a couple of corrections as this was done quick.
I concur with Michael, although this works to an extent it has some major drawbacks.
The big one is the tuning gang, it has to be totally isolated from each other, you could use two separate capacitors that were mechanically connected via say plastic gears or a toothed belt but this is OTT, or even varicap diode tuning. Also it is insensitive, it needs an RF stage and even with two stages of IF amplification it's not great with only the stronger stations being acceptable. So yes it does work but it's severely limited. I'm sure other rod Pentodes would work and much better than trying this approach. I've used these little 6v valves for other projects and they work very well indeed and intact using them in a TRF configuration with both control grids strapped the performance is excellent.
I wanted to try an infinite impedance detector but as yet I've not worked out the best way to do this with a filamentary valve, suggestions are welcome. So this superhet project is now shelved.
Addendum. The 150pf cap is wrongly drawn, it should be in series with the oscillator coil not in series with the choke to the G2.
I attach a quick drawing of the circuit, there's a couple of corrections as this was done quick.
I concur with Michael, although this works to an extent it has some major drawbacks.
The big one is the tuning gang, it has to be totally isolated from each other, you could use two separate capacitors that were mechanically connected via say plastic gears or a toothed belt but this is OTT, or even varicap diode tuning. Also it is insensitive, it needs an RF stage and even with two stages of IF amplification it's not great with only the stronger stations being acceptable. So yes it does work but it's severely limited. I'm sure other rod Pentodes would work and much better than trying this approach. I've used these little 6v valves for other projects and they work very well indeed and intact using them in a TRF configuration with both control grids strapped the performance is excellent.
I wanted to try an infinite impedance detector but as yet I've not worked out the best way to do this with a filamentary valve, suggestions are welcome. So this superhet project is now shelved.
Addendum. The 150pf cap is wrongly drawn, it should be in series with the oscillator coil not in series with the choke to the G2.
