08-09-2021, 08:25 PM
(This post was last modified: 08-09-2021, 08:37 PM by Murphyv310.)
Hi.
Today I bit the bullet and tried a 1J24B in the RF stage. The result was mixed. Sensitivity was up but G2 regeneration didn't work. In fact the radio worked exceptionally well. Spirit Radio on 549 was very strong as was BBC R4 on 720. There was some bleeding though from 1035 my local and 810 BBC R Scotland. Winding more turns around the ferrite rod didn't help. Increasing the anode load resistor value brought back regeneration but output was then no better than the 1j42a and was less stable, the valve was fed from the 54v HT line, it also was badly microphonic. I then tried a 1j18b it did admittedly work more like the 1j42a but the reaction was far from smooth and was peaky, tuning was also displaced, perhaps caused by a different G1 to F capacitance. Again without reaction the output was excellent but did suffer with bleed from the strong stations.
I've now returned the RF stage to the 1j42a. It is lower output on the low level stations on speaker but plenty of volume on headphones.
So I'll be now leaving the radio as is.
Next projects in my mind is another pantry transmitter using a 1j37b. Also a superhet again with 1j37b, 1j24b x2 and perhaps a 1j24b, will see. Lastly a single valve FM radio, I've already made one with a 1j29b using super regen. Not sure as yet what way I'd go with it but may use a 1j37b. Don't hold your breath though since covid restrictions have been lifted we are back doing some charity work so time is more limited, this week though some external work is being done on the house so I've not been out and have had time to play.
Today I bit the bullet and tried a 1J24B in the RF stage. The result was mixed. Sensitivity was up but G2 regeneration didn't work. In fact the radio worked exceptionally well. Spirit Radio on 549 was very strong as was BBC R4 on 720. There was some bleeding though from 1035 my local and 810 BBC R Scotland. Winding more turns around the ferrite rod didn't help. Increasing the anode load resistor value brought back regeneration but output was then no better than the 1j42a and was less stable, the valve was fed from the 54v HT line, it also was badly microphonic. I then tried a 1j18b it did admittedly work more like the 1j42a but the reaction was far from smooth and was peaky, tuning was also displaced, perhaps caused by a different G1 to F capacitance. Again without reaction the output was excellent but did suffer with bleed from the strong stations.
I've now returned the RF stage to the 1j42a. It is lower output on the low level stations on speaker but plenty of volume on headphones.
So I'll be now leaving the radio as is.
Next projects in my mind is another pantry transmitter using a 1j37b. Also a superhet again with 1j37b, 1j24b x2 and perhaps a 1j24b, will see. Lastly a single valve FM radio, I've already made one with a 1j29b using super regen. Not sure as yet what way I'd go with it but may use a 1j37b. Don't hold your breath though since covid restrictions have been lifted we are back doing some charity work so time is more limited, this week though some external work is being done on the house so I've not been out and have had time to play.
