Insulation stress in tube output transformers

On a sunny day (Tue, 24 Feb 2015 18:51:19 -0800 (PST)) it happened Lasse Langwadt Christensen wrote in :

Also slighty related:

At such low frequency, did it use lumped components or transmission line components, requiring a lot of metal work as when operating with that tube in UHF ?

Things are easy these days with the microstrip constructions usable to several (tens) of GHz.

Note the huge number of vias going to the bottom ground plane. Usually lamda/10 is considered the maximum distance between the vias, but this has far more vias, possibly to avoid some problems at harmonics.

It started to be difficult at UHF, due to the wiring distances in the tube and the transit distance from cathode to anode.

The external-anode coaxial tubes (4X150A and up, 4CX250A etc) were much easier at UHF:

The VOR transmitter had lumped component grid circuit with a couple of turns in the coil and a small butterfly capacitor. In the plate side, there was a center-tapped hairpin loop and another butterfly capacitor. There was a second hairpin and a series-tuning capacitor to pick the output.

On a sunny day (Sat, 28 Feb 2015 12:48:31 +0200) it happened snipped-for-privacy@downunder.com wrote in :

Not sure what you mean, the army thing was just two metal tubes with a shorting strip IIRC, connected to the 2 anodes of the tube. Any copper tubing would do, silvered would help. Lechers are simple (to tune):

It the danger from RF radiation now (at GHz) versus the danger of high voltages in the old days at RF. I had 1 kV with big oil capacitors in my linear.

Heat conductance? There is a large copper heat spreader under the PCB.

I very much doubt that.

That is called the ground plane for RF :-). It is an organic part of a microstrip construction. It may also help in spreading heat around.

Look at the ground ring around the top side of the PCB. For a one off project, one would have simply used some copper tape, wrapped around the edge of the PCB, soldered to both the ground plane below the PCB as well as the ground areas on the top side of the PCB. For mass production, using frequent vias would be cheaper.