06-09-2025, 03:22 PM
The only way to know for sure is to measure it. It would be lovely if the OP is willing to experiment for us. Just a volt meter connected across that cap is all that is needed - just to see what the range of voltages are in practice.
In the absence of data, I thought it would be useful to have an idea of the range of DC voltages one could expect from the detector diode. Most of my radios are in storage, and of the handful that are on display downstairs, they're either not very representative of the set in question, or would require too much dismantling for my liking (I've got a lot on today). So the best I could do is the Hacker Sovereign II. The AM IF PCB is under a screening cover, but it is possible to probe the audio output, which is fed almost directly from the diode - just a potential divider of 1k into 4k7.
I found this voltage varied between low 10s of mV between stations up to nearly 2V (1.95V) on the strongest stations. Radio 4 LW was nearer 1.8V. These are negative voltages (this set uses NPN transistors).
I'm not assuming these numbers are the same as you'd find in the GEC set, but if we pretend that they were for a moment, we can quickly determine that a positive bias is possible: if we ignore the base current and assume a HT of 8V, we'd have +0.7V at the base. As the BE junction is now reverse-biased, ignoring Ib was OK, probably...
This isn't a "slam dunk" - we are talking about 2 fairly different sets - but it shows that might just be possible.
I do take the points made above, of course. Perhaps this is why AGC evolved to include 2 IF stages in many cases? This GEC is a very early transistor set.
In the absence of data, I thought it would be useful to have an idea of the range of DC voltages one could expect from the detector diode. Most of my radios are in storage, and of the handful that are on display downstairs, they're either not very representative of the set in question, or would require too much dismantling for my liking (I've got a lot on today). So the best I could do is the Hacker Sovereign II. The AM IF PCB is under a screening cover, but it is possible to probe the audio output, which is fed almost directly from the diode - just a potential divider of 1k into 4k7.
I found this voltage varied between low 10s of mV between stations up to nearly 2V (1.95V) on the strongest stations. Radio 4 LW was nearer 1.8V. These are negative voltages (this set uses NPN transistors).
I'm not assuming these numbers are the same as you'd find in the GEC set, but if we pretend that they were for a moment, we can quickly determine that a positive bias is possible: if we ignore the base current and assume a HT of 8V, we'd have +0.7V at the base. As the BE junction is now reverse-biased, ignoring Ib was OK, probably...
This isn't a "slam dunk" - we are talking about 2 fairly different sets - but it shows that might just be possible.
I do take the points made above, of course. Perhaps this is why AGC evolved to include 2 IF stages in many cases? This GEC is a very early transistor set.
