29-07-2022, 10:27 PM
Hello Mike, it will take some time for me to take in what you have printed here. I will have to bring up the circuits of the sets you mention (If I have them) to try and follow what you are saying. I had been reading through some of the posts by Joe Sousa on the Radiomuseum site and it was the statement of: - 'Model r326, by Aleksandrov Radio Works in Russia, uses the 1ZH37B dual grid pentode in mixer service.' That made me want to try it and I have assumed that the rf input onto one grid and the local osc on the other grid would give isolation between the antenna and local osc. If I am reading the thread correctly from Joe although the valves seem to be rated to 60 MHz, his tests suggest they will work considerably higher frequency. I was going for a separate local osc valve as I thought it easier to construct and get right, it even allows me to use one of my signal generators as a local osc source initially while getting the mixer stage working.
It is all learning exercise for me, just to see if I can using these valves, because I will have them? I do appreciate the thread I mentioned gives a good account of them as an agc stage.
This is what I had in mind, sorry for the quickly hand drawn sketch.
OK I can start to appreciate it may not work as expected, but could you please clarify something for me
'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.'
I am struggling a bit to understand this and wonder if this is the type of thing you mean: -
If not could you do a simple hand sketch some time.
I am considering a second mixer stage down to 455 at some point going from 10.7 to 455 for NBFM, in effect having two demodulators. I think I can see that it is easier at 10.7 to 455 because the centre tapped transformer could be tuned for a single frequency and not across 88 to 108 or what ever band I go for.
Head hurts.
Cheers
Adrian
It is all learning exercise for me, just to see if I can using these valves, because I will have them? I do appreciate the thread I mentioned gives a good account of them as an agc stage.
This is what I had in mind, sorry for the quickly hand drawn sketch.
OK I can start to appreciate it may not work as expected, but could you please clarify something for me
'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.'
I am struggling a bit to understand this and wonder if this is the type of thing you mean: -
If not could you do a simple hand sketch some time.
I am considering a second mixer stage down to 455 at some point going from 10.7 to 455 for NBFM, in effect having two demodulators. I think I can see that it is easier at 10.7 to 455 because the centre tapped transformer could be tuned for a single frequency and not across 88 to 108 or what ever band I go for.
Head hurts.
Cheers
Adrian
Learning as I go!
Youtube EF91 Valve
Youtube EF91 Valve
