[Amps] Is This 4CX1600B Still Good?

[Ian White GM3SEK]

Hello Mike


>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.
>
Please can you let me have more specifics about which components had 
failed?


>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




-- 
73 from Ian GM3SEK