Hello,
Thanks for the heads-up.
The cathode is hard grounded to the chassis as that was one of the
electrical checks I did and visually confirmed. Unfortunately that
is the case as it would have been an easy and inexpensive fix.
At 03:53 PM 11/22/2005, you wrote:
>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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>
>
73,
Mike, K4GMH
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