Water Cooled 23cm Amp

I came across a pre-built pa module as described in the UHF-Unterlage, by K. Weiner DJ9HO.

It is described in chapter D.5.6. I have owned this book myself for many years.

2C39BA is used in this project and I have a couple of them in the drawer.  


Max anode dissipating is 100W stated from the manufacturer (Siemens) however much more is available. There are many topics on the net showing different styles.

100W out is probably ok with forced air as anode cooling, however I will try to maximize the output with water cooling. I’m not sure what the output will be, but 12 to 13db gain and 10W drive could reach 200W output. I have heard that 11W drive is the crital point, higher drive will destroy the tube.


Of course will the tube life be shorter but the hours with high output on SSB will not be so many anyway. And I actually have a bunch of them. They are only funtionally tested, newer used./2c39ba.jpg




I made the cooler from brass. Easy to cut and easy to braze.





The original anode cooler is re-sized smaller and mounted back to the tube to make the water cooling more efficient. The cooler is made of brass and silver brazed togheter. The tube anode is soldered to the cooler with 300°C solders.





I will use 2 HV transformers that I had in my junk box.  They are 115V primary so 2 will suite me fine. The secondary will be connected in parallel and they deliver about 1000V 250mA each.

To the left is the cavity module.





I used an exhaust gas cooler and did some re-building. Different pump and added water tank etc. The outlet water temperature is measured, and it is possible to drain the system via a solenoid valve. The water flow rate can be adjusted with a needle valve.






The back of the unit. I use quick connectors which is normally closed this makes connection / disconnection easy.







The PA with tube mounted.








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