Garey Barrell [EMAIL PROTECTED] made an utterance to the drakelist gang
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Bill -
Bias voltage is relied on to open the relay by cutting off the 6EV7
relay tube and if that voltage is low because of leaky electrolytics or
ripple in the Bias supply in the AC-3/4., the tube doesn't cut off as
quickly. Since you have eliminated the supply, another possibility is
that the 6EV7 is slightly gassy, which again causes tube to want to
continue conducting after it is told to cut off, especially after long
transmissions! Yet another possibility is that the final tubes are
dropping in emission, which requires you to set the bias voltage more
positive to set the idle current to the proper value, again resulting in
reduced negative voltage to cut off the 6EV7. Lastly, there are several
very high value carbon composition resistors in the biasing for the VOX.
ANTI-VOX and Relay circuits that can increase in value with age,
resulting in insufficient cut off bias for the 6EV7.
A rule de thumb is that the bias voltage at the Final grids is typically
-60 to -65VDC for nominal idle current.
Let us know what you find!
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B C-Line Service Supplement CDs
www.k4oah.com
Bill Ellis wrote:
Recently having put my T-4XB/R-4B combo back on the air after 1 year
off, I'm finding that when I put the T-4XB in spot mode, I can't get
the relay to return to the receive mode. This is not keying the
finals(I don't think), it just seems to hang up in the spot mode.
About 3-4 years ago, I had rebuilt the AC-4(cap's and all), so I don't
think that is the problem. Now I know the the anti-vox and vox delay
affect how long the relay remains engaged.I have tried that
combination with no success. I could just be getting the wrong combo.
My question is where is a good starting point for these two controls.
Also, could this be a bad 6EV7?
Thanks for any help 73's
Bill, WB9CAC
Tempe, Az
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