trying to fit it all in.

[Opcom]

Started sketching some ways to fill the rack with the power supply and RF stuff for the future 3CX3000 amplifier covering 2-30MHz +6M.

The rack might be barely enough. I would like to have it a bit more roomy because one goal is to convert the RF deck- a Henry 14Mhz 5KW RF generator, into a 6M amplifier as seen on the web in a few places. This is shown to be very compact and all fit in the existing RF chassis. It uses inductive tuning and no 'tuning' cap at the plate.

From there, adding a PI tank for HF right above it and quite close to the tube should be do-able. I'm exploring the idea of using the 2-30MHz HF PI coil as part of the RF choke for the 6M amplifier. In the original HF amp the coil is from, the B+ feed was through that coil and its insulated for it. That method no doubt helped the original amp hit 30Mhz and avoid resonances in any plate chokes making trouble, since the voltage across the RF chokes in the original amp was at the "50 Ohm" end of the pi coil.

To so this, some HV vacuum switches or low-capacitance  switches are needed, and they have to be rated for goodly current plus have 40-80dB isolation (a figure in the data sheet, no idea how it was calculated), and 10-20KV ratings. I have one of them, a Jennings, a bit overkill at 50KV.

I'm thinking about keeping the 6M tank coil in at all times to reduce lead lengths at high frequencies, and its cold end feeding the hot end of the original pi coil. For HF operation, this 6M coil would be set to minimum inductance (shorted turn tuning), and the Jennings vacuum switch having very high isolation and low inductance would disconnect the 6M loading cap from the cold end of the 6M pi coil. For 6M use, the HF pi could would be set to 160M (2MHz) position and used as the top end of the plate choke.

There are possibly other ways to switch  things around. possibly the 6M loading cap could also be the HF tuning cap. The only difference I know of would be the voltage rating requirement and the ability to cover the capacitance range. There are probably enough vacuum caps around here to do that with one of them.

I realize this is not a normal thing done but that is OK. I do not mind experimenting if things are well thought out. I believe it can be done if attention is given to lead lengths, the series inductance of capacitors including the path around the cap for RF, and the capacitance of the HF PI inductor to ground and self. I have no problem with unconventional mounting, such as hanging the HF PI stuff right above the tube, close in.

Anyway the attached is a drawing of a possible layout in a 6 FT rack, of everything except the RF deck and control circuits, meters, etc.

From this it looks as though I might want to use the 'cubicle' approach that BC transmitters use, my apprentice suggested it, that is two racks in this case. One for power and one for RF. It would give me more room to add the tuning devices for 6M ad HF bands for the RF section.
He said, do it like the nuclear physics experiments, stuff sticking out (from the tube) in every direction. With a separate roomy cabinet for the RF stuff, and the good examples of the 6M 3CX3000 RF decks, it seems like the HF pi section could be hung just above the tube, no reason it has to be beside it like on a normal HF amp. Thinking in 3D not 2D. If I did not want 6 meters, it would all probably fit but still be tight.

I am not very interested in downsizing the power supply or blower or variac, getting rid of the MV rectifier tubes (the blue things in the front window) or the choke, or adding the cheapness of electrolytic capacitor stacks to this. It really should be the last amp I'll ever need and I don't care how large it is, only how long-lasting and reliable for full power AM use.

The point is to show some layout ideas for the existing/available cabinet, and ask about whether a second rack for the RF section would make sense and make the whole thing easier to deal with. I don't have to use this cabinet. I think there is a pair of identical 6 FT racks in the back corner.  if nothing else I drew a pretty picture.

Lastly, the tuner for balanced line could be also included in the top, if the RF section had its own 6 FT rack. This would solve lots of "tuna" problems here.