Some of the older, "built like a brick Scheiße-Haus" kw broadcast transmitters, used 575A's to run 2500-3000 volts to 833A's. But the later "Lite" versions of the 833A kilowatt rigs by the same manufacturers used 872A's, which seemed to work OK up to 3 kv or so. IIRC, the PIV of 575A's is 15 kv, while that of 872A's is 10kv. 10kv piv should be ok up to 3100 volts DC using the full wave midtap circuit. Apparently when the manufacturers cheapened their rigs, they decided the extra 50% safety margin was unnecessary, and with good 872A's, rectifier flash-over was never a problem if they were operated properly. I believe 575's and 872's run at the same filament voltage, so they should be directy interchangeable. Four 872A's (or 4B32's) in a full wave bridge should be good for about 6 kv at 1 amp.
I haven't tried to build my own solid state rectifier stacks for many years, but back in the 60's and 70's I never could get them to work very long before having a firework display, no matter what equalising resistors and by-pass capacitors I used, or how many extra diodes I included in the string for safety margin. So, with several bushels of mostly used 866A's, 3B28's, 872A's and 4B32's on hand and plenty of filament transformers to run them, I have always stuck with hollow state rectifiers. I use commercially built, direct replacement solid state 872A's and 866A's in my Gates BC1-T and after 5 years they have never given me any trouble. I replaced the 5R4 bias rectifier with diodes purchased brand new (don't recall if I used two in series for each leg or just one in each leg) but I used the highest piv diodes I could find and so far, no problem with those, either. I solid stated the bias rectifier to free up the octal socket, to hold the 6AS7G I use as a DC regulator to isolate the protective bias tap that allows me to run the Gates on CW. Don k4kyv _______________________________________________________________ This message was typed using the DVORAK keyboard layout. http://www.mwbrooks.com/dvorak/ http://gigliwood.com/abcd/ ______________________________________________________________ Our Main Website: http://www.amfone.net AMRadio mailing list Searchable Archives: http://www.mail-archive.com/[email protected]/ List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Post: [email protected] To unsubscribe, send an email to [email protected] with the word unsubscribe in the message body. This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
