[Amps] Is This 4CX1600B Still Good?

[TexasRF@aol.com]

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 at 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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