14-11-2015, 10:32 AM
(This post was last modified: 14-11-2015, 10:33 AM by Murphyv310.)
Hi.
The detector is a leaky grid setup, the bias is derived by the 2 meg grid leak and the 0.0003 grid coupling capacitor, this circuit requires no additional bias.
The actual valve is of little importance virtually any 2 volt Triode will work even those allegedly for audio. HT on the first stage can be from 45 to 100v dependent on the choice of valve, trial and error being the best approach.
The subsequent stages, audio amplifier and output require bias but again its down to the valves in use, this is one reason the grid bias battery has so many taps as there were so many different valves around with small variations in characteristics, again trial and error is the best way, your looking for maximum output vs distortion.
Brilliant projects these little TRF's. I've now made at least two using the Russian Rod Pentodes. They work very well and the sensitivity is quite amazing.
I've built a short wave one too, hope to catch Radio Australia soon!
The detector is a leaky grid setup, the bias is derived by the 2 meg grid leak and the 0.0003 grid coupling capacitor, this circuit requires no additional bias.
The actual valve is of little importance virtually any 2 volt Triode will work even those allegedly for audio. HT on the first stage can be from 45 to 100v dependent on the choice of valve, trial and error being the best approach.
The subsequent stages, audio amplifier and output require bias but again its down to the valves in use, this is one reason the grid bias battery has so many taps as there were so many different valves around with small variations in characteristics, again trial and error is the best way, your looking for maximum output vs distortion.
Brilliant projects these little TRF's. I've now made at least two using the Russian Rod Pentodes. They work very well and the sensitivity is quite amazing.
I've built a short wave one too, hope to catch Radio Australia soon!
