Testing-Device for GU74b / 4CX800 tubes
It seems that the exchange of GU74b / 4CX800 tubes in Amplifiers like Alpha91b, Acom2000A, and Acom1000 is more interested than originally expected. In my post on how to replace the tubes of an Alpha91b I explained in depth why it is so important to recondition, to “getter”, the tubes at least 24 hours before any other voltage can be applied. Often amplifiers apply automatically HV and grid voltages which makes them unsuited for the gettering process. My Buddy Matthias, DK4YJ built recently a simple device that makes the heating and testing of tubes much more convenient.
All is needed is a plastic box, one or two tube sockets, a few plugs, and a fan
The plugs on the front allow good access to the individual pins of the tubes. This makes troubleshooting more comfortable.
When NOS tubes are reconditioned, heating voltage is applied for at least 24 hours. Even if just a few watts of heat are produced, a constant airflow ensures that the tubes stay cool. Any 12V fan will do the job.
Thanks to Matthias, DK4YJ for sharing these pictures.