[NLRS] 432 Cavity Amp project (formerly know as "FQA Special ) - Final Report

[Paul Husby]

Excellent work, Ron!  I think K0FQA just smiled...    -Paul W0UC

On 10/26/2019 12:59 AM, Ronald Bergantzel via NLRS wrote:
> Hello All . Well , as I promised I am sharing how the old FAA Rockwell /Collins amplifiers from the K0FQA estate turned out . I finished the first unit after striping It from its original configuration  and performing a couple of simple modifications to the output cavity . My results are as follows : 1150 watts output with just under 50 watts drive from my FT991( output power was measured using a Bird 43 with a 2500 watt slug )  . The full technical specs are : 3100 vdc Plate voltage at 690ma Plate current( key down )  . Screen voltage was at 485vdc and aprox 5 ma ( key down ) , Grid voltage was -65vdc ( key down )  with a zero signal idling Plate current of  170 ma .  With the amplifier's configuration  the input and output cavities are tuned both at the same time , although at the 1150 watt power output the input SWR was 1.7:1  I think it can be improved upon some while still maintaining the 1100 watt plus output level .....
> The low points of the project were the amount of time that was required to assemble the amp ( read - parts chasing ) . My next 432 amp will be a full legal limit version ( amp #2 )  with more cooling on the amp as well as going to a 7/16 DIN output connection . I have 4 of the cavities already stripped and modified and ready for a chassis with 4 more stripped from the original chassis awaiting for me to do the mod to the output cavity - I have salvaged the tube base pieces from the first cavity I disassembled for my reverse engineering  - and am curious what the RCA / Burle 4661 tetrode tube would perform like on 6 m ?? Also , with 20 some cavities , tubes , etc  I will probably build up a spare half wave cavity amp  for 144 like the GS35 workhorse  I currently use ( using in a grounded grid configuration) .
> Anyway , it's looking like I should be on 432 with some QRO during the contests - I need to complete an outside ( at the antenna ) box for my T/R relays and preamp  - maybe by next month for the last leg of the ARRL 50 - 1296 EME Contest : we will see .
> Thanks to all of the NLRS gang  who helped me acquire these at Jon;s estate . 73 , Ron KA0RYT EN35ct
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