[JMS] Need biasing info on 90881 amp/812A's

Sat, 14 Feb 2004 20:35:07 GMT

All:
Has anyone successfully put their Millen amplifier using the cathode modulation configuration recommended by the company? Of concern is the "biasing" needed for the 812A p-p configuration of the 90881 amp. I took a page from the Svetlana site on 812A p-p AUDIO/MODULATOR specs and it says you need around -40 VDC for CCS operation. I will probably use this voltage for the RF configuration of the P-P amp but just the same, does anyone have any design considerations or concerns they'd like to throw in before I build the supply?

BTW, I have started obtaining parts for the unit. A new 10.5" steel rack plate has been ordered along with a pair of nice looking handles I bought from the hardware store. I also have a Hammond 800 VCT 465 mA transformer I'll be full wave bridge rectifying. Output will be about 1120 volts but with a 10 HY choke I found, I think I can bring it close to the 1040 VDC at 217 mA cited by the Millen data sheets for cathode modulation. 

Also, I have a 600 VCT 250 mA Hammond iron for the modulator/transmitter circuitry. I'll be taking another full wave bridge and choke for my plate supplies but I will take an additional choke and cap filtering system and put it on the center tap for the screen voltage supply. 

Also, I ordered up several pilot lamps to give my transmitter that "KW-1" look. One for the filaments, one for the transmitter/mod, and one for the plate supply to be put near the top edge of the power supply plate. Let me know your thoughts and thanks!

Cal, N6KYR. 

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