08-10-2021, 07:25 PM
Hi.
I've modified the original again and now down to two 1ZH24B valves. The first one is an RF amplifier with positive feedback derived from the G2 fed back to the ferrite rod with 8 turns of litz wire around the ferrite rod slightly off the centre of the rod. Tuning remains the same as previously. The anode of the RF amp is loaded with 2x 2mh chokes in series, they are modern ones which have a high capacitance, using two improves the low end of the band. The HT end of the chokes are decoupled by a 100pf cap and the HT is dropped by a 15k resistor. We need to have a lower Anode volts to use the G2 for feedback. The feedback winding is directly connected to the G2, the earthy end goes to a 5k pot the other end goes to HT via a 1k resistor the junction is decoupled by a 1nf cap.
The detector is as the original with a small addition of an added 1m resistor from filament plus to the G1, this removes distortion caused by non linearity in the detector. The AF amp is as previously without the output valve. I'll redraw the circuit soon.
On strong stations with minimal reaction it's a bit too loud on headphones, audio quality is clean with little or no distortion, weak stations come up well advancing the reaction with Radio Caroline coming in well at 20.10 this evening with the radio sitting on the arm of my chair in the living room.
HT is 54v
I've modified the original again and now down to two 1ZH24B valves. The first one is an RF amplifier with positive feedback derived from the G2 fed back to the ferrite rod with 8 turns of litz wire around the ferrite rod slightly off the centre of the rod. Tuning remains the same as previously. The anode of the RF amp is loaded with 2x 2mh chokes in series, they are modern ones which have a high capacitance, using two improves the low end of the band. The HT end of the chokes are decoupled by a 100pf cap and the HT is dropped by a 15k resistor. We need to have a lower Anode volts to use the G2 for feedback. The feedback winding is directly connected to the G2, the earthy end goes to a 5k pot the other end goes to HT via a 1k resistor the junction is decoupled by a 1nf cap.
The detector is as the original with a small addition of an added 1m resistor from filament plus to the G1, this removes distortion caused by non linearity in the detector. The AF amp is as previously without the output valve. I'll redraw the circuit soon.
On strong stations with minimal reaction it's a bit too loud on headphones, audio quality is clean with little or no distortion, weak stations come up well advancing the reaction with Radio Caroline coming in well at 20.10 this evening with the radio sitting on the arm of my chair in the living room.
HT is 54v
