UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Questions on 160/80 metre AM transmitters.

AdrianH · 11th Jan 2023, 10:40 pm

Thanks for that.

If I am reading it correctly and trying to apply this to the CODAR seesaw arrangement of the autotransformer, I would need to see at what point the mod anode drops to without distorting and if this is, say 25 Volts then I would need to drop 25 Volts across a resistor on the opposite side of the autotransformer, then C would have to be suitably large so as to bypass at the normal audio range.

So if it was 25 Volts at 40 mA R would be 625 Ohms and to pass a 100Hz audio signal without loss C would need to be just over 25uF which is a reactance of around 62.5 Ohm.

Interesting, it may not be worth trying for near 100% modulation, but an extra few percent to 90 may be worth a try.

Cheers

Adrian

ps I wonder if it would need to be a non polarised cap, it should not but I could see a lot of stress on a standard electrolytic.

11th Jan 2023, 10:40 pm	#138
AdrianH Octode Join Date: Mar 2020 Location: Blackburn with Darwen, Lancashire, UK. Posts: 1,572	Re: Questions on 160/80 metre AM transmitters. Thanks for that. If I am reading it correctly and trying to apply this to the CODAR seesaw arrangement of the autotransformer, I would need to see at what point the mod anode drops to without distorting and if this is, say 25 Volts then I would need to drop 25 Volts across a resistor on the opposite side of the autotransformer, then C would have to be suitably large so as to bypass at the normal audio range. So if it was 25 Volts at 40 mA R would be 625 Ohms and to pass a 100Hz audio signal without loss C would need to be just over 25uF which is a reactance of around 62.5 Ohm. Interesting, it may not be worth trying for near 100% modulation, but an extra few percent to 90 may be worth a try. Cheers Adrian ps I wonder if it would need to be a non polarised cap, it should not but I could see a lot of stress on a standard electrolytic. __________________ Asking questions and learning, or trying to! Youtube EF91Valve Last edited by AdrianH; 11th Jan 2023 at 10:48 pm.