Eddy -
Absolutely. This particular situation is probably one of the few cases
where just bridging a suspect cap is indicated. Rather than leakage at
DC, which will drag down the cathode voltage, I'm suspecting a high ESR,
or 'dried out' cap. The purpose of this cap is to bring the cathode to
AC ground, while R44 sets the DC bias point of the stage for Class A
operation. When the ESR of this cap goes up, the cathode rises above AC
ground, applying negative feedback and reducing the gain of the stage.
Actually any time high ESR is the suspected problem bridging is
suitable. IF leakage or shorting is suspected, not so much!!
Your power supply caps 'bulging' is almost always the result of DC
leakage currents, in which case bridging would be totally inappropriate.
Just as an aside, If you've ever had to replace C131, you know that you
'really' don't want to if it's not necessary!!! :-)
73, Garey - K4OAH
St Charles, IL
Drake Service Supplement CDs for
2-B, 2-C/NT, A, B and C-Line,
TR-4 and TR-4C
Diane and Edward Swynar wrote:
/*Hi Garey et al,*/
/**/
Some very good points made re. this thread, no doubt about it...
However, when it comes to capacitors, I personally /_don't_/ subscribe
to the notion of /bridging/ any suspect unit with a good one: far
better to /remove/ the suspect cap out of the "hot" portion of the
circuit entirely, & temprarily replace it with the good one that way.
I've had electrolytics bulge & fail on me in the HV capacitor string
of my 2.5 KVDC p.s.---the /last/ thing I'd want to do there is bridge
a good one across a suspect filter cap! The bad one would effectively
negate any "good" that the new cap might bring with it to the party...
Just my $0.02 worth...
*/~73!~ de Eddy VE3CUI - VE3XZ/*
*//*
***************************************
----- Original Message -----
From: "Garey Barrell" <[email protected] <mailto:[email protected]>>
To: "Joe Loverti" <[email protected] <mailto:[email protected]>>
Cc: <[email protected] <mailto:[email protected]>>
Sent: Tuesday, December 28, 2010 11:24 AM
Subject: Re: [Drakelist] R-4A low audio output
Joe -
I'd sub out the 6GX6 and the 6EH5 first. If no luck, (or if you don't
have tubes handy,) you could check R44 for value. A dried out C131 will
drop the gain considerably, you can bridge it with any electrolytic you
have handy to check. The cathode voltage should be pretty close to 3
volts.
Beyond this will take more investigation.
73, Garey - K4OAH
St Charles, IL
Drake Service Supplement CDs for
2-B, 2-C/NT, A, B and C-Line,
TR-4 and TR-4C
Joe Loverti wrote:
> I have a 13-tube, R-4A receiver that is an excellent performer and fun
> radio to use – except for one issue: the audio output seems to be a
> bit low: Is it normal to have the volume control at nearly 1 o'clock
> for normal, comfortable listening? Other Drake and non-Drake receivers
> seem to have a comfortable audio level about 9 o'clock. Is there a way
> to boost this receiver's audio output or is there something obvious to
> check? Any suggestions always appreciated. Thanks in advance and happy
> holidays to all the Drake list folks.
>
> WW8X
> Joe Loverti Sr.
> Miamisburg, Ohio
>
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