From: Garey Barrell 
Subject: Re: [drakelist] B line Help Please


Tim -

The relay hanging is probably a gassy 6EV7.  It's possible that C91, the bias 
supply capacitor mentioned below is the culprit, but most likely the tube itself.

The rest of your problems are probably being caused by dried out electrolytic 
capacitors.

C90A-D, the four section twist-lok cap; C91, the bias supply filter; C172 & 
C173, the audio stage decoupling capacitors (most likely the cause of your 
specific problem); C190 the low voltage calibrator decoupling capacitor; and 
C192, the low voltage filter cap are all likely suspects.  If you have a scope 
or ESR meter, you can find the particular one(s), but if not replacing all of 
them will take your receiver for the next 30 years.  All are easy to find, with 
the exception of the four section twist-lok.  There have been several suggested 
replacement techniques offered.

1.  Clip the leads off the bottom of the can, install a four terminal tag strip 
and put four discrete caps under the chassis.

2.  Remove the existing cap, cut the can just above the base crimp and remove 
the "guts".  Install four, (or three if too tight,) discrete caps
inside the can 
and epoxy back in place.

http://www.thecompendium.net/radio/filtercap.htm>

3.  Remove the can and install an octal socket (easier to find than the 5 pin 
mentioned) in it's place.  Mount four discrete caps on an octal plug and plug it in.

http://www.geocities.com/maxmartin3/drake/r4b.html>

4.  Clip the leads off the bottom of the can and place the four caps wherever 
they will fit under the chassis.  Lead length is not critical, so they can be 
"scattered" around.

++++++++++++++++++++
Keeping the original can intact but disabled, I ended up installing three
100 uF {at} 250v caps and one 22 uF cap underneath the R-4B. It was a tight
fit, but two 100 uF axial caps and the 22 uF fit snuggly in a cluster next
to S-meter adjust pot. The other 100 uF cap fit with not a hair to spare
between the phones jack and chassis. The arrangement let me keep the same
lead lengths of the wiring harness. The cap switchout was a preventative
maintenance measure more than anything, as the original 1967 vintage cap was
still chugging along...but for how long...

FYI, I got the caps from Mouser Electronics...pretty cheap, too...

73 John K7FD
++++++++++++++++++++

John posted a picture, but apparently it is no longer available.

73, Garey - K4OAH
Atlanta

Tim English wrote:

> Have a few problems with my B line I am hoping I can't get some answers 
> to here.
>  
> 1. On my T4XB, you set the relay delay for a resonable delay time, then 
> after a long cw xmission the relay hangs and wont release until you turn 
> the delay pot way back. Then it wont key again until you run the delay 
> pot back up a ways. Doesn't seem to be a happy medium. Could this be a 
> problem with the 6EV7 VOX tube ?
>  
> 2. On my R4B, all cw signals sound like they have a slight ac ripple to 
> them and not a pure tone. The receiver seems sensitive enough just the 
> cw signals done sound clean. Also my calibrator is not working. Anything 
> I can check for on these items ?
>  
> --
> Tim, K8TJ
> (ex-WB8OGM)
>  
>  

----------------------------------------------------------------------
Submissions:        drakelist{at}www.zerobeat.net
Subscribe:          majordomo{at}www.zerobeat.net - subscribe drakelist in body
Unsubscribe:        majordomo{at}www.zerobeat.net - unsubscribe drakelist in body
Hopelessly Lost:    majordomo{at}www.zerobeat.net - help in body of message
Brought to you courtesy of TLCHost.net  http://www.tlchost.net/
----------------------------------------------------------------------

---