Henry RF AMPLIFIER

Ip & RF Output Slowly Increases

After Keying Amplifier

 NE7X - 04/19/2012

On my Henry 2K-4 RF amplifier I noticed when running continues carrier RTTY on 20 meters, after the amplifier was keyed for transmit the plate current (Ip) would start at about 500ma and then slowly increase to about 580ma after about 2 seconds. I also noticed during this time the RF output would slowly increase from about 800 watts to 1000 watts output. Something was not correct, I should have full Ip and RF output "immediately "after I keyed the amplifier, and only 1000 watts output maximum was a bit low for a Henry 2K-4.

 

To troubleshoot and identify the problem,  I asked myself:

1) Does it do this on all bands or only one band?

2) Does the HV drop when first keyed, then slowly increase?

3) Does the RF input from the transceiver slowly increase after the amplifier was keyed?

4) Is the SWR between the transceiver output and amplifier input good?

5) Does the bias voltage slowly increase after keying?

Possible Causes:

1) If the issue is only on one band, its most likely something in the input circuit for that band, or one of the Silver Mica HV capacitors in the RF output circuit for that band.

 

2)  Check all the HV power supply electrolytic filter capacitors. Check all diodes in the HV chain for a leaking (not shorted) diode. If the diode was shorted you would be blowing fuses or have HV arcing

 

3/4) Place a SWR meter in-between the transceivers output and the amplifier's input.

    Does the RF power slowly increase after keyed?

    Is the SWR a good match?

Check the amplifiers tuned input circuit, may needs alignment.

 

5) Check the bias zener. Make sure its not leaky or shorted.

 

So what did I finally find which was causing this issue? 

 

The 3-500Z tubes were soft. I replaced both tubes and now when the amplifier is keyed, Ip goes immediately to 800ma with no delay and RF output goes immediately to ~1400 watts.  Now this is how a Henry 2K-4 should operate !!!

  

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