Hi Mike, all of your voltage readings should be measured from the cathode
terminal or as close to the cathode terminal as possible. There are several
failure scenarios that would allow those voltage readings if you are using the
chassis or ground as the reference for the readings. If you are absolutely
positive, no chance for error, that the cathode is hard grounded to the chassis
then of coarse this is not applicable information.
73/k5gw
In a message dated 11/22/2005 2:37:03 P.M. Central Standard Time,
k4gmh@arrl.net writes:
Hello,
Need guidance on whether the tube, 4CX1600B, is still good after an
amp. failure during the ARRL Sweepstakes SSB Contest.
When the amp. went out there weren't any flashes or smoke just no
output and no high voltage. The amp. was still drawing ~380 mA but
no screen current. G3SEK Tetrode boards are used in the amp. but had
not tripped off. (The Boards have saved the tube several times from
operator error.)
Trouble shooting the homemade amp., the screen voltage was found to
be 20 V. The shunt regulator's diode string was shorted. The diodes
were replaced and, after checking out the other components in the
regulator (one resistor was double its marked value - replaced), the
regulator was tested and measured 330 V.
The 4CX1600B was reinstalled in the amp. however now there is no
ZSAC. The ZSAC should be around ~350 mA. Checked the voltages, 3100
V anode, 330V SG2, -56 V SG1, 12 VAC fil. Cathode grounded. Also,
there is no reduction of the anode voltage to indicate the tube is
drawing current. Previously, the anode voltage would be reduced ~100
V when the amp. is keyed with no drive.
The amp. and tube are over eight years old and have been used almost
exclusively on RTTY (1200 Watts) and some CW. The ARRL SSB Contest
was the first extensive SSB use of the amp.
73,
Mike, K4GMH
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