07-09-2021, 08:12 AM
Hi Amie.
I've found that Rod Pentodes of any type oscillate very easily. The level of signal at the G2 is actually higher than anticipated. As you can see on my circuit only two turns of litz wire are used for the "tickler" and this is adjusted by varying the HT on this grid. The advantage of a low number of turns is the reaction is easier controlled and smooth, you just want it to oscillate not turn into something unstable and uncontrollable, so many make this elementary mistake of having too many turns on the feedback winding then have to alter the circuit to get a compromise and land up with a stage that virtually has no gain and or poor control over reaction. On this one reaction is so smooth with no adjustment required between 1.5mhz and 750khz then a progressive rise to 530khz but very controllable.
I've made TRFs before using PCF80s but this one I have to say is the best one to date. I'm seriously considering that I'll leave the 1J42A in circuit and not trying the 1J24B, it most likely will need even less FB with perhaps just one turn. I'll see what transpires today or tomorrow. If it works well I'll do my usual YouTube video with the results. Following the openness of Glasnost if it doesn't perform as well then I'll let you know.
I've found that Rod Pentodes of any type oscillate very easily. The level of signal at the G2 is actually higher than anticipated. As you can see on my circuit only two turns of litz wire are used for the "tickler" and this is adjusted by varying the HT on this grid. The advantage of a low number of turns is the reaction is easier controlled and smooth, you just want it to oscillate not turn into something unstable and uncontrollable, so many make this elementary mistake of having too many turns on the feedback winding then have to alter the circuit to get a compromise and land up with a stage that virtually has no gain and or poor control over reaction. On this one reaction is so smooth with no adjustment required between 1.5mhz and 750khz then a progressive rise to 530khz but very controllable.
I've made TRFs before using PCF80s but this one I have to say is the best one to date. I'm seriously considering that I'll leave the 1J42A in circuit and not trying the 1J24B, it most likely will need even less FB with perhaps just one turn. I'll see what transpires today or tomorrow. If it works well I'll do my usual YouTube video with the results. Following the openness of Glasnost if it doesn't perform as well then I'll let you know.
