[Amps] Born: 4-400A Amp

[John]

Gents -- My first posting here.  After six months of periodic intense effort, I have successfully managed to use up a bunch of parts that I found I couldn't sell at hamfests.  Gathering dust before, but now in use, is a huge Thordarson Plate transformer; a 4-400A (equivalent) tetrode; two 15 KV vacuum variables; two huge 5-pos. ceramic band switches (from 40's surplus); purchased K2AW rectifier modules and one used Jennings vacuum TR relay; countless 100- to 200-watt resistors, a power-pole capacitor (a guess), two 19-inch panels with meters and one rack.
    One bandswitch has three day-time bands plus an "other" position and the other bandswitch also has three night-time bands plus an "other" position so that the tuning for resonance will remain tuned for the operator's favorite for day or night.  A relay biases off the tube when receiving.   Basic low-pass filters for each band between the K-3 output and the 4 : 1 step-up balun at the tubes filament are currently switched out with a bypass jumper, because originally the step-up balun was not used and trying to get the PI LC filters to step up the impedance as well as filter (using a higher Q) failed.  Now that this balun is in place and tests are showing a nice low SWR back to the K-3, simpler LC LPF's using a Q of 1 will be reformulated and installed ASAP.  The amplifier works well on the 160 through 10 meter bands by taking advantage of the terrific bandswitches, ceramic coil forms, and transmitting capacitors for loading that were found in my junk box.  Each band has its own series inductor in the 3-pole LC PI output circuit.  Two 97-uHy RFC's were used in series to fully choke the amplifier on 160 meters (one above and one below the chassis). 
    I laughingly use fish line, sinkers, and a yard stick to tell the relative capacity that either resonance variable is tuned to, since these are not your usual variable capacitor.  You know that I can do better than this. Lol.  But it works.  I'm probably going to have to spend money on this amplifier and get some turns counters on thes large dials.  The good news is that at resonance the grid current meter increases, as it should, and the plate current dips, as it should, resulting in getting good gain and efficiency from the tube.  In GG, it has a pretty high plate resistance compared to more modern tubes so using 3500 VDC on it still results in a pretty cool running outfit.
The tube stays black now that I'm switching the cathode (filament) current off in-between transmissions.  On a good day it will produce 450 watts for my inverted vees and Mosley TA-36.
    My trusty H.B. 4-1000A amplifier was constructed about 15 years ago and is every bit as reliable as a "boat anchor".  A pun is intended.  All of this is just FYI.  Don't let anybody badmouth boat anchors!  Racks still take up less space than a pool table.  Good luck with yours.
John Sherrick, W8OHT
PO Box 1585
Fort Ashby, WV