Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Martin -
Something is shorting the final cathodes to ground, "South" of the meter
shunt, R59.
There are a limited number of paths that can get the cathodes to ground,
especially when that path has to handle the idle current you are seeing
in the "key-up" condition.
Heater-cathode short in V7, (6AU6 AM Mod tube). ?
I've never measured the key-up Final cathode voltage, but I think it
could rise as high as the screen voltage if the cathodes are "open" to
ground?
73, Garey - K4OAH
Atlanta
Drake C-Line Service Manual
<http://www.k4oah.com>
Martin Sole wrote:
"Martin Sole" <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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I checked the bias voltage at the tube bases. The AC4 pot varies it between
about -44 volts and -85 volts. If I key the radio in SSB (No Mic gain) and
advance the bias pot until the meter shows 0.1A, bias voltage measures about
-55 volts,then release the PTT the current increases to approximately 0.12A.
Same problem with different PA tubes that were known good last time they
were tried in another radio.
Looking at the cathode line it seems this is taken to ground by a contact on
K1 but when unkeyed should rise up to cut off the tubes. How many volts
should be on the cathode line in the unkeyed state? On this radio the point
at L5 sits around 0.38 volts in the unkeyed state and drops to 0.34 volts in
the keyed state. Voltages are the same with K1 removed.
Ideas appreciated.
73
Martin HS0ZED
-----Original Message-----
From: Gary Poland [mailto:[EMAIL PROTECTED]
Sent: 06 September 2005 10:22
To: Martin Sole
Subject: Re: [drakelist] T-4XC permanent current problem
Martin,
Sounds like you have lost a capacitor in the AC-4 bias supply. The voltage
is too positive causing constant plate current.
73, Gary
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