02-09-2021, 06:32 PM
(01-09-2021, 08:57 PM)Murphyv310 Wrote: Hi.
On my 1J42A pantry transmitter if I varied the control grid voltage of the one that wasn't used for the oscillator feedback, the result was the resultant output varied as per the DC applied. This is logical as I used this grid for the AF input. The 1j37b of course is bi control grid as well. I'd say that using these Bi grid valves that AGC could be applied to one grid.
One project I started was using a 1J42A as a frequency changer, my issue was the lack of coils etc but I did use one grid for local osc and the other for RF input, there was a resultant IF at the anode. It wasn't very good and I got fed up with it and abandoned the whole thing. I'd say the 1j37b would be a better proposition though. May go back to it one day using the higher voltage valves.
I love the video Trevor. You have got them very well and your radio works well too!
If I may I would just like to give the (probably rather rough) figures I gathered from my 1j37b mixer setup today. I know that your mixer / oscillator setup is different but the figures I give may be of some value. I didn't mention in my earlier post (because I completely forgot) that I had tested it earlier with a FET oscillator I have been working on. I put this together inspired by an LTSpice example circuit, just adding a buffer amplifier. with a view to possibly building a valve version at some point, although it may be more sensible to stay with the FET for stability, drift etc. Using this for local oscillator and my signal generator for signal input. As previously mentioned the 1j37b mixer is followed by an emitter follower matching to a 455kHz ceramic filter then to a two stage 1j24b IF amp. All the valves have single coil tuned circuits, currently tuned to 455kHz. With the setup I provided a capacitor feeding a 47kOhm resistor as a nominal load. During testing all coils, when loaded by the oscilloscope probe, were retuned as required. All testing / measurements were done using the oscilloscope so frequency measurement, particularly, is nominal. My signal generator, and the measurement equipment, are limited so the minimum setting on output is used which is somewhat higher than ideal. This may well mean limitations in accuracy etc but I think the gist of things is correct. Due to things being a bit of a lash up I am limited. The results (all voltages p to p). HT supply 60V (except oscillator):
Signal input 12mV 1.16 MHz to 1j37b g1a
Oscillator drive 1.5V 1.61 MHz to 1j37b g1b
Frequency changer (ceramic filter) output 120mV 455 kHz (noisy waveform but may be effect of probe or setup).
First IF amp 1j24b output on second IF amp grid resistor (100kOhm) 5.4V
IF amplifier output (across 47K load) 58V
As yet I have only used unmodulated signals although the signal generator output is messy. I think the figures show that this is a goer but careful signal handling will be needed. The circuits I use tend to follow the Russian examples, the actual mixer here being closely influenced by that of the R-326 military radio.
If anyone has any questions please don't hesitate to ask.
Tracy
