Bill -
I'm guessing here, since you didn't specify. Do you mean when you key
the transceiver you have NO PLATE current, or LOTS of PLATE current???
Assuming you have NO PLATE current, which is most likely, consider that
the PA tube normally want to draw as much current as possible when
keyed, the BIAS is to LIMIT that current. If this is the case, then the
transceiver PA is not really being keyed. Since you have eliminated the
PS as the problem, there are only a couple of things to check.
First, has the TR-4C been modified for use with TC-2 or TC-6? If it
has, then there must be a jumper connected between two jacks on the
upper rear panel to apply Screen voltage to the PA.
IF not, then 'something' is open. IF the voltages on the PA tubes are
correct, e.g., 650 VDC on plate caps, 260 VDC on Screen pins, and the
Cathode is grounded, the PA WILL draw maximum current. Pin 3 of each
final tube goes to a 15 ohm, 1W resistor. All three resistor leads then
go to RFC2. The other lead of RFC2 connects to a ceramic feedthrough on
the shield wall to R45. The other lead of R45 goes to a relay contact
that is grounded in transmit. If this circuit is unbroken, including
the relay contacts closing, and the Plate and Screen voltages are
correct, the PA WILL draw current. Regardless of ANY other fault or
problem in the transceiver.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>
Billy Loyd wrote:
I have a TR-4C that I cant set the bias on. When adjusting the bias
control on the power supply it has no effect on the radio. I have 2
power supplies and both have no effect. I can remove the bottom cover
from the supply and set the bias to the proper - voltage using my volt
meter but it does not set the bias on the radio. Where do I start looking.
Tnx in advance for the help....de Bill......KY4U
PS. I have checked the cable from both supplies and the connector on
the radio for loose connections but nothing wrong there.....Bill
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