08-11-2020, 04:06 PM
Got back to this for a short time today.
I've finally decided to try a 1J42A as a pentode mixer. Strapping the two grids together gives the best RF gain and feeding the oscillator into the G2 gives the highest conversion signal at the anode. The G2 volts is quite critical at 3v for best results. Good results are with 4v P-P drive although between 2. 5 to 5v makes little difference on the scope. The output from the IF is very low though, even feeding it into the TA7642 doesn't give much audio so we either will need to add a stage of RF or IF amplification.
The time now is to consider whether I should scrap the idea of using the 1J42A valves and using the 1J24B types instead. Using the 1J24B's unfortunately means a higher HT and then we will need three different battery supplies so less than elegant, especially for a pocket radio.
So now some time to hit the drawing board and engage the brain!
I've finally decided to try a 1J42A as a pentode mixer. Strapping the two grids together gives the best RF gain and feeding the oscillator into the G2 gives the highest conversion signal at the anode. The G2 volts is quite critical at 3v for best results. Good results are with 4v P-P drive although between 2. 5 to 5v makes little difference on the scope. The output from the IF is very low though, even feeding it into the TA7642 doesn't give much audio so we either will need to add a stage of RF or IF amplification.
The time now is to consider whether I should scrap the idea of using the 1J42A valves and using the 1J24B types instead. Using the 1J24B's unfortunately means a higher HT and then we will need three different battery supplies so less than elegant, especially for a pocket radio.
So now some time to hit the drawing board and engage the brain!
Cheers.
Trevor
MM0KJJ. Member of, RSGB, GQRP, WACRAL, K&LARC.
Trevor
MM0KJJ. Member of, RSGB, GQRP, WACRAL, K&LARC.