07-09-2025, 07:04 PM
The BC506 has only Vbe across the electrolytic with no signal, which is about -0.15V (wrt emitter)
The BC504, BC505, Decca TP33, Decca TT33 and Vidor Gem CN440 all have two caps. A small 40nF to 100nF effectively on base-emitter via IFT and electrolytic on the AGC line (effectively base to 0V via IFT). The electrolytic thus has about -1 V with no signal.
Actual Vidor Gem / CN440 on capacitor has about -1.4V with very little signal (background noise). About -1.1V on strong interference. I'd need to connect sig Gen. No AM here.
Emitter about -1V with no signal and -0.85V with the interference.
Supply from 6V battery pack about 4.7V at R8, and 4.9V at main power in.
PCB
Maybe tomorrow I'll connect sig gen
The BC504, BC505, Decca TP33, Decca TT33 and Vidor Gem CN440 all have two caps. A small 40nF to 100nF effectively on base-emitter via IFT and electrolytic on the AGC line (effectively base to 0V via IFT). The electrolytic thus has about -1 V with no signal.
Actual Vidor Gem / CN440 on capacitor has about -1.4V with very little signal (background noise). About -1.1V on strong interference. I'd need to connect sig Gen. No AM here.
Emitter about -1V with no signal and -0.85V with the interference.
Supply from 6V battery pack about 4.7V at R8, and 4.9V at main power in.
PCB
Maybe tomorrow I'll connect sig gen
