04-07-2020, 12:32 PM
(This post was last modified: 04-07-2020, 12:40 PM by Murphyv310.)
Hi.
Here is the circuit I am using.
The first stage is an RF amp with positive feedback to the ferrite rod via a winding of two turns, ideally the 4.7k pot should be returned to HT and then to the coil rather than the way I did it, the 2Mh choke from the G2 to HT keeps the gain of the valve up as the HT stays constant with adjustment of the reaction pot when the feedback is reduced, this makes the reaction far more progressive than without it.
There is no grid resistor on the AF amp even using a 10 meg reduces volume somewhat, I have also tried a little forward bias on the diode to see if weak stations come in any stronger with no improvement.
The 2nf decoupler on the anode of the AF amp is important as is the HT decoupler. Results are quite spectacular with 12 stations on medium wave last night three foreign stations were listenable last night with no external aerial.
I've made a few TRF sets over the years and I can in all honesty say this performs far better than any. The AF gain is far higher than I thought you would get from these little valves. A simple and easy project to do.
Without reaction I still can receive three stronger stations at good volume so there is very good gain between the stages.
I also agree with Tracy these valves are getting scarce.
HT is 9v
Here is the circuit I am using.
The first stage is an RF amp with positive feedback to the ferrite rod via a winding of two turns, ideally the 4.7k pot should be returned to HT and then to the coil rather than the way I did it, the 2Mh choke from the G2 to HT keeps the gain of the valve up as the HT stays constant with adjustment of the reaction pot when the feedback is reduced, this makes the reaction far more progressive than without it.
There is no grid resistor on the AF amp even using a 10 meg reduces volume somewhat, I have also tried a little forward bias on the diode to see if weak stations come in any stronger with no improvement.
The 2nf decoupler on the anode of the AF amp is important as is the HT decoupler. Results are quite spectacular with 12 stations on medium wave last night three foreign stations were listenable last night with no external aerial.
I've made a few TRF sets over the years and I can in all honesty say this performs far better than any. The AF gain is far higher than I thought you would get from these little valves. A simple and easy project to do.
Without reaction I still can receive three stronger stations at good volume so there is very good gain between the stages.
I also agree with Tracy these valves are getting scarce.
HT is 9v
