23 Apr
2005
23 Apr
'05
2:31 a.m.
From: "Tony Duell" <ard at p850ug1.demon.co.uk>
Whether there existed sets with, say, an EB91 (double diode, I think you
call it a 6AL5) for the FM detector and an EBC91 (say) for the AM dector,
AGC, and 1st audio, I don't know, and I am not looking for such a
schematic tonight!.
-tony
The Hacker Mayflower 2 I have on the bench at the moment uses an EB91 as FM
detector, but appears to have no AGC (it is FM only). The is a preset (rear
mounted) sensitivity control on the 1st IF though. I suppose the idea is
that you were a set distance from the transmitter, so the sensitivity (gain)
could be fixed - when this set was built, FM broadcasting consisted of 3
stations (Third, Home and Light), all from the BBC, so the transmitters for
a certain area would be co-located.
There are a few other FM sets that use the EB91, but I don't have any to
hand to look how the AGC is derived.
Jim.