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Gerry
I apologise for the delay in getting back to you
but I was diverted to some domestic duties :-))
All of the components you mention are present in
this R4C, S/N 24601. None of the components show any signs of physical
damage though I confess I haven't gone so far as to remove the ceramic caps to
confirm they still hold their original values.
I confess my only experience with ceramic caps
going OC was related to physical damage to the cap. Much more common were
SC failures due to overvoltage. Is OC failure due to ageing something
folks see with these devices? If there is a real chance that healthy
looking devices might have gone SC I can remove them to check them
out. Though you will know that's no small undertaking. Meanwhile,
the addition of a 10 nF ceramic cap across C76 has completely resolved the
problem with negligible impact on medium and slow agc times.
Many thanks.
73 Bob, 5B4AGN
----- Original Message -----
Sent: Thursday, May 26, 2005 10:00
PM
Subject: RE: [drakelist] R4C agc
problem
The AGC
characteristics of R-4C receivers depends on the version of the receiver.
There were at least two that I know of. Furthermore, modifying agc time
constant was something that may individuals tried way back when. There were
several articles dealing with that subject including one in the March 1980
issue of CQ magazine in which the author modified his R-4C to mimic the
Collins 75S3-B. Maybe this is because fast, medium, and slow is subjective and
everyone has their own idea of what it should be. Nevertheless, the fast AGC
position in the stock R-4C is much too fast for my taste and lacks filtering
so I added a 0.05 uf capacitor from Q7 collector to ground to suit myself. As
it is, the R/C combination of C43 a 0.01uf capacitor and R16, a 1 meg resistor
as well as C75 a 0.0024 uf capacitor provide a bare minimum of filtering. If
there is motorboating, I would check these components and make sure they are
in the circuit and working properly. Additionally, C76 a 0.001 uf capacitor
may also be opened. The fast AGC position is meant to be used on CW and
possibly AM. It was never intended to be used on SSB. The R-4B agc is a
similar design but with different values of gain and time constants. The fact
that the R-4C has sharper bandpass IF filters accentuates the
problem.
-----Original
Message-----
From:
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On Behalf Of
[EMAIL PROTECTED]
Sent: Thursday, May 26, 2005 5:23
AM
To: [EMAIL PROTECTED];
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Cc:
drakelist@zerobeat.net
Subject: Re: [drakelist] R4C agc
problem
I agree
with Mark about the AGC issue you have described. The audio will have a
somewhat distorted sound at times when in the fast AGC position. Slowing
the AGC release time down just a bit will resolve that issue. I
personally never use the Fast AGC position. I have owned many Drake receivers
over the years and have found this to be common. I doubt you really
have a problem.
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