Spent yesterday doing final punch list items like installing the bottom plate and anchoring in the power supply cage cover. This has been a rewarding project insofar as addressing the many small obstacles and technical issues. Regrettably this project is somewhat depressing as it also now fully convinces me I should have gone into the amateur radio equipment manufacturing business. Too late now.
In giving this a bit more thought the whole project involved an Engineering Team consisting of one person... me. Just think what I could have really done with a bigger team.
There were no kits or BOMs involved, and the rig has parts from over 55 years ago, while at the same time it blends mostly old technology with new technology. It required writing CNC software to cut the various metal pieces and a lot of engineering and tribal knowledge to pull it off. In essence this was a totally homebrew project including the power supply. One of the nicest comments I received was that it looked factory made
A bit of info on the 12GE5 RF Amp stage. The Plate voltage is 500VDC, the Screen at 280VDC and the bias set to deliver 25Ma of Cathode current. The Bias to the rig is -120VDC. The Bias network connected to the tube has the range to deliver 25Ma of Cathode current.
I did not have a 6.8K 2-watt resistor so I paralleled four 27K, 1/2-watt resistors and that worked FB. The Cathode Meter is a 0 to 200Ma unit and it connects to Pin4 on the Plus side, and the Minus side is connected to ground. Pin 4 and Pin 10 each have a 10nF, 1KV ceramic cap to ground. Again, the Meter on the Plus side to Pin4 and the Minus side to Ground.
The 20nF cap connected to the 6.8K and the center wiper on the bias pot actually puts that resistor to ground for any AC signals.
The plate circuit is not built as shown on the sketch. The inductor is a HB choke (227 Uhy , 24T #2o on a FT-82-43) and it connects to a parasitic choke comprised of two 100 Ohm resistors in parallel that have three turns of #24 wire and that connects to the plate.
At the junction of the parasitic choke and the RF Choke you connect a 1000pF 20KV cap which feeds a Pi Network. The Pi Network Tune Cap is 150pF and the Load Cap is 1000pF comprised of a 600pF trimmer cap in parallel with a fixed 330pF cap. The Tank Coil is 15 Turns (8 TPI) and 1.25 inches in diameter. Pin 12 on the Filament is grounded. The feed from the IRF510 into Pins 3/11 Via a 10nF passes 1st through a W3NQN LPF.
For added safety a Home Brew 2.5 Millihenry RF Choke is connected from the Pi Network to ground in the event the Plate Coupling Cap shorts you would have 500 VDC on your antenna. The RF Choke would shunt that voltage to ground. The RF Choke is 73 Turns of #28 on a FT-82-43 core AL = 470
The Stainless-Steel expanded metal screws into the angle stock.
Nice and Safe!
Bottom Plate with Countersunk screws
Fit Check of Rubber Feet
I have been back at the Sketch parameters and did a bit of fine tuning on the BFO frequency. It sounded a bit nasal and pinched and I made some changes there. But for the most part we are done. Well, my rigs are always built as experimenters' platforms and so never done!
So, this is the recovery from the ill-fated Transcom SBT-3, Project X and it helps that this Mostly Vacuum Tube Wireless Project was successful.
Them that know, really do know and can make it go.
73's
Pete N6QW