(07-03-2017, 02:25 AM)Nowhere-Man Wrote: A simple thing I noticed tonight about the Saalburg schematic is the EZ80 is heated on the same winding as the other valves. This is apparently typical of the EZ80. Interesting that the EBF89 which is a double diode pentode, has a diode passed to ground and the grid used in IF amplification.
Based on the diagram so far I have a feeling the first knob is where I'm losing the voltage but ECC85 is not effected.
EABC80 so far is a bit over my head - triple diode triode.
You may wonder why ponder the schematic so much. The answer is I'd like to better understand the circuit before going in a bit deeper. Whereas at first I was clueless it now gradually makes a bit more sense.
The EBF89's diodes were sometimes configured as a detector diode and separate AGC diode, but as you've observed that's not the case in this receiver because just one diode provides both AM detection and the AGC voltage, that now makes the 3rd diode in the EABC80 redundant, originally the diodes in the EABC80 were designed to provide FM detection using two of its diodes and AM detection/AGC using the 3rd diode, the EABC80 might look a bit complicated but it's not, two of the diodes share a common cathode with the triode, the other diode has a separate cathode, one of the common cathode diodes along with the separate cathode diode is used for the FM detection, the other common cathode diode would have been used for AM detection/AGC but not in this receiver because that function is being performed by one of the diodes in the EBF89.
Hope this helps.
Lawrence.
