Tim -
Good suggestion! I've never run into that, but V13A is the Receive AGC
amplifier, and an intermittent internal short could very well crank the
AGC up, cutting off current flow through V11 and unbalancing the bridge.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line & TR-4/C Service Supplement CDs
<www.k4oah.com>
Bolbach, Timothy wrote:
My experience in this case has been a problem with the AGC amplifier
V13. The circuit voltages will check ok, the tube will check fine in an
emission tester. But, the 12AX7 will be bad. Starts intermittently and
becomes worse as time goes on. Try replacing the 12AX7.
Regards,
KD8CN
-----Original Message-----
From: drakelist-boun...@zerobeat.net
[mailto:drakelist-boun...@zerobeat.net] On Behalf Of Garey Barrell
Sent: Tuesday, September 15, 2009 3:13 PM
To: drakelist
Subject: Re: [Drakelist] TR-4C annoyance
Loren -
A full scale S-Meter is typical of a receiver in Standby, or in the case
of the TR series, when it's switched to transmit. Standby in the
transceiver can be approximated by turning the RF GAIN full CCW. Does
the S-Meter go to the same reading in both Standby and fault conditions?
The meter circuit is a bridge, and depending upon model various tube
currents are compared to the AF Output tube current. So anything that
causes those currents to change will result in S-Meter action. In the
TR-4C, those tubes are V4, and V11, compared with the AF Output tube
V17. When the transceiver is in Receive mode, the cathodes of the first
two tubes are grounded by a pair of contacts on K1, causing the bridge
to be balanced and the meter is set to ZERO by adjusting ZERO on the
left side of the radio. When the cathodes are allowed to float, in
transmit, those tube currents go to zero and V15's cathode is grounded,
causing the S-meter to read upscale with transmitter AGC action. In the
alignment procedure R187, under the chassis, is adjusted to cause the
meter to read full scale when the RF GAIN control is turned full CCW in
Receive.
I would check the tube voltages around V4 and V11 to see if there might
be a fault at the sockets or in the wiring to K1. Something is causing
the current in those two tubes to decrease considerably. It's also
possible than one of the tubes may have an internal fault.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line & TR-4/C Service Supplement CDs <www.k4oah.com>
Loren McCullough wrote:
Lately, my TR-4C has developed an annoying quirk. Shortly after
turning it on (sometimes immediately, sometimes after 10 minutes or
so), the S meter will go nearly full scale and stay there. Usually
keying the mic several times will stop this and it will return to
normal operation (only has done this once after turning on, then is
normal for the rest of the time I have it on). It does not appear to
be in transmit, as I can hear the relay clicking on and off as I key
the Mic.
Any ideas on this one?
Loren - WA3WZR
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