[AMRadio] Pw Supply

John E. Coleman (ARS WA5BXO) wa5bxo2006 at pctechref.com
Thu Dec 7 17:11:33 EST 2006

The 813 will operate just fine at 1500 volts on the plate and 135ma or 270ma
for two tubes that is about 400 watts input or 300 watts RF output.  Grid
current for two tubes should be 32 ma and grid leak bias at 150 volts.
Screen voltage about 300 volts.  A little bit more voltage on the plate and
you would be at or about the legal limit with full sine wave modulation.  To
stay legal I would run a little less voltage so that the audio peaks don't
go over the 1500 watt limit while running voice because of asymmetrical
voice wave forms. See http://www.qsl.net/wa5bxo/asyam/aam3.html

John, WA5BXO

-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net] On Behalf Of Geoff/W5OMR
Sent: Thursday, December 07, 2006 3:41 PM
To: Discussion of AM Radio in the Amateur Service
Subject: Re: [AMRadio] Pw Supply

Jack Schmidling wrote:

> In plate modulated AM service, the 813's will run nice
> at 2000 volts on the plates at 400ma for 2 tubes.

Just looking at the spec's, Jack, for a single 813...  in Ham service, 
they say you can run 2500v on the plates, at 225mA, but in the same 
chart, says the max is 450w max.  Sorry... the math just don't add up.  
But, if you use a single 813 in the final, and modulate it with a pair 
of 811's, you'll be at, or over the 'legal limit' anyway.

Either way, 1500w PEP is the Maximum Power Output we're allowed to run 
these days.  Not like in the old days, when 1kW DC input, measured at 
the plate of the output tube(s) was the law (and a helluvalot easier to 

73 = Best Regards,
Every Day of Freedom is a Good day to Thank A Veteran.

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