Re: [drakelist] R4C agc problem

[Eric Webner]

It sounds to me, Bob, like you are on the right track. Perhaps the 1nf cap on fast needs replaced. Incidently, I generally don't use fast agc, even on cw. It allows the noise in between characters to come up. Just sounds a little annoying, that's all.

 

Good luck on your R-4C. I need to clean up and align mine, but it seems to work well. Just got a 500 Hz filter to go with 250 Hz, so now I am really ready for cw!

 

73,

 

Eric KA8FAN

Bob Henderson <[EMAIL PROTECTED]> wrote:

"Bob Henderson" <[EMAIL PROTECTED]>made an utterance to the drakelist gang
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Hi Garey

I guess you're thinking the problem is 120 Hz from the half wave rectifier.
That ocurred to me briefly but in Cyprus we are on 50 Hz and the strange
modulation is at ~150 Hz. This seems rather odd. Nonetheless, I checked
the bias line and added a further filter cap for good measure just to rule
this out. The problem continued.

I looked at the agc time constants and see that for fast there is a 1nF cap,
for medium a 47nF in series with 220k is placed in parrallel with it and
then for slow a further 220nF in series with 33k is added in parrallel with
both.

The audio sounds clean with medium and slow agc but terrible with fast. I
can't quite work out what's going on just ! now but I've put a 10nF cap in
parrallel with the 1nF at C76 and the audio cleans right up. I guess this
makes the fast agc position slightly slower than intended but it's still a
lot faster than the medium setting.

I guess this means the problem has gone away, though I haven't worked out
why it was there in the first place.

I guess, if I knew what I was doing, I might be dangerous :-))

Thanks.

Bob, 5B4AGN


----- Original Message -----
From: "Garey Barrell" <[EMAIL PROTECTED]>
To: "Bob Henderson" <[EMAIL PROTECTED]>
Cc:
Sent: Wednesday, May 25, 2005 6:47 PM
Subject: Re: [drakelist] R4C agc problem


>
> Garey Barrell <[EMAIL PROTECTED]>made an utterance to the drakelist
gang
> ----------------------------------------------------------------------
> Check the filter capacitor for the Bias supply.
>
> 73, Garey - K4OAH
> Atlanta
>> Drake C-Line Service Manual
>
>
>
>
> Bob Henderson wrote:
>
> >"Bob Henderson" <[EMAIL PROTECTED]>made an utterance to the drakelist
gang
> >----------------------------------------------------------------------
> >Hi all
> >
> >I recently picked up an R4C which I'm now checking out. It's in pretty
good
> >all round condition and for the most part seems to work well. However, I
> >notice a particular problem with the agc. If I set agc to medium or
slow
> >then all appears well but if I select fast the rx sounds awful. I scoped
> >the af output from the rx and notice that when fast agc is selected, the
> >audio output appears 50% modulated by a ~150 Hz ripple. It's not
> >immediately obvious to me where that is coming from.
> >
> >Something is clearly not right here! . I wonder if any of you fellas have
> >seen this before?
> >
> >73, Bob, 5B4AGN
> >
> >
> >
> ----------------------------------------------------------------------
> On Behalf of Garey Barrell <[EMAIL PROTECTED]>
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> Unsubscribe: [EMAIL PROTECTED] - unsubscribe drakelist in
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