It's Alive!! The Old Henry 2K4 Makes RF Power

[Charlie Young]

It's not dead Jim! 

Today I put the safety RF choke across the tank circuit, to replace the one that someone removed.  It is a safety hazard to run without this choke, although the amp would make power without it.  You don't want high voltage DC getting into the RF components of an amplifier, which is what happens if a plate blocking capacitor fails.   They sometimes do fail.  

Afterwards I hooked the rig (FT2000) up to the cold amp to make sure the RF was feeding through the relay from input to output connector.   It was open.   There were two issues.  One was a broken wire on the relay contact.  The other was an extremely dirty relay contact.  With these problems fixed,  the rig fed power through to the amp relay to the dummy load. 

Next, I cranked up the HV and keyed the rig with a bit of RF drive (10 watts) on 80M.   The plate current meter deflected up a bit over idling current.  Rotating the tune and load controls, I was able to see a bit of power out.  We peaked for max at 10W drive, then started raising the drive level. 

There being no arcing or smoke, we kept increasing drive and adjusting the tune and load.  At about 600W output from the amp, the keying circuit stopped.   Oops.  Pulled out the schematic.  Decided to check the simple stuff first.  Unplugged the RCA keying cable from the amp female receptacle.  Pushed it back on and moved it around.  Amp keying worked.  I pulled the cable plug back out and gave the receptacle a bath with contact cleaner.  It works now. 

Continued increasing drive on 80.  Stopped at about 80 watts.  All was OK.  Power output was about 1100 W key down.   I could see the plates red in both tubes, which is normal, but it is obvious one of the tubes is soft compared to the other.  You can see the difference in the plate coloration.  I knew this tube condx from the original idling current test, the RF test confirms it.  The pair is usable as-is, the thing is putting out much more than the legal limit power from when it was built.   

I might have another Eimac tube or two lurking around here, unknown condx.   If so, I might use the Henry as a tube tester. 

At some point the amp would benefit from a matched pair of 3-500 tubes.   I will put in it the best working pair of Eimac tubes we have here on hand.  It will be up to a future owner to replace the tubes 🙂. 

So far, we have resurrected this using only junk box parts. In fact, other than a bad tube and the missing safety choke, the amp was in pretty good shape for its age. The major defect was a failed disc capacitor.   It could really use a good cleaning. 

Next up, check it for RF on all bandswitch positions. 

Even the meters work 🙂. 

The dang thing is impressive looking, for sure.  It would need more HV to put out power like an AL-82, but looking at the RF deck, the components might take it.  This amp is in the same class as a SB220, Ten Tec Centurion, LK-500 Amp Supply.   Like the Heathkit, it does not have 160M.  I would say the Henry is built heavier duty than the others mentioned. 

73 Charlie N8RR

[Larry Fravel]

Awesome Charlie!

K8YYY

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[N8NN Bert]

Charlie -- So interesting!  Your troubleshooting process is not only logical and instructive, it is also entertaining.  Thanks for telling us about the amp project repairs.

Bert N8NN