[Drake] Sick R4C

[W7RY]

-----Original Message-----
From: Larry Taft [mailto:ltaft at charter.net] 
Sent: Thursday, April 27, 2006 10:12 PM
To: W7RY
Subject: Re: [Drake] Sick R4C

Tape a piece of cardboard over the S meter.  Now, tune in the calibrator

on one of the low bands, say 80 meters.  RF gain full CW, audio gain 
straight up.  With a good speaker on the old girl does the signal sound 
LOUD? 

No

 If so, try connecting a good antenna to her. do you get the Band 
noise well above the receiver noise?  If so then it sounds like the 
basic receiver is working.

No

Take the cardboard off the S meter.  Most problems with the S meter are 
the tubes that form the bridge circuit so try new tubes.  What does the 
S meter Zero control do?  What does turning the RF gain full CCW do?  
Should go to full scale

All tubes checked or replaced

The 35 volts on pin 6 of V3 (which I show as a 6BE6, 40 VDC) is probably

OK as the voltage table has a bit of windage allowance in it.

The voltage table shows it should be 75 volts. Not what I would call
tolerance.


As I said above S meter is usually tubes........ usually.  After that I 
don't have any magic bullets, just trace through the circuit.  Once in a

while a diode goes bad too.  Or a leaky cap...

Thanks
Jim


73, Larry  K2LT
drakerepair.com    800-687-9161
 

W7RY wrote:
> I have acquired an ailing R4C. The sensitivity is low. A 50uV signal
> will barely move the S-meter. 
>
> I've noticed that the voltage on pin 6 of V3 (6HS6) is low, only about
> 35 volts. I think the problem is somewhere in the AGC circuit.
> I have searched the archives and have found few clues.
>
>
> Ideas? 
>
> Thanks and 73
> Jim W7RY
>
>
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