Has anybody encountered a problem with a Grundig 650? Here is the
problem...........if I have the AGC turned off, and the RF Gain control
turned up to maximum, everything is ok.
When I enable the AGC, the interstation noise has a howling crackling
quality........also, the receiver's gain is about 10dB lower. It almost
sounds like a bad AGC capacitor; if it is leaky, the gain of ther I.F.
system will be lower. A clue to this possibility is the crackling sounding
static. This is a characteristic of an envelope detector diode not
completely "turned on" by the I.F. signal.
Does anybody have any ideas? I am going to open up the unit this
evening......unfortunately, the closest thing I have is a model 600
schematic.

Pete

Pete KE9OA wrote:
Has anybody encountered a problem with a Grundig 650? Here is the
problem...........if I have the AGC turned off, and the RF Gain control
turned up to maximum, everything is ok.
When I enable the AGC, the interstation noise has a howling crackling
quality........also, the receiver's gain is about 10dB lower. It almost
sounds like a bad AGC capacitor; if it is leaky, the gain of ther I.F.
system will be lower. A clue to this possibility is the crackling sounding
static. This is a characteristic of an envelope detector diode not
completely "turned on" by the I.F. signal.
Does anybody have any ideas? I am going to open up the unit this
evening......unfortunately, the closest thing I have is a model 600
schematic.

Don't leave out the idea of badly designed AGC. I have one old GE AM-only
handheld radio I've been experimenting with on and off; it started out
pretty nicely sensitive, but I found out through tinkering that the AGC
was holding it back. In this 9V radio, I ended up putting something like
six 1N914's in series with the AGC line before the AGC stopped attenuating
weak signals.

I gotta get that thing back on the bench, especially now that I found the
schematic I drew (sloppy but effective). I had a real hoot experimenting
with various stuff on there.

--
If John McCain gets the 2008 Republican Presidential nomination,
my vote for President will be a write-in for Jiang Zemin.

I've got one of those 2999s. It is a very decent LW/MW receiver. The Grundig
650 has very similar performance on these bands. As I was playing with the
650, I noticed the effects of reciprocal mixing on the 19M band. Plenty of
sideband noise out of this synthesizer.

Pete

"rkhalona" wrote in message
oups.com...
Most likely a bad AGC capacitor. I had the same problem with my
Philips D2999.
I actually replaced the capacitor with a larger one (found by trial and
error) and that gave me a nicer AGC response (less pumping).

RK