[AMRadio] 813/811 Rig

Brett gazdzinski brett.gazdzinski at verizonbusiness.com
Sat Nov 11 21:48:57 EST 2006

The 811 is not the best choice as a modulator tube
to match the 813's.
The 813's like to run at 2000 volts, 400ma, 600
watts of carrier output.
A pair of 811a's like 1200 or 1500 volts, and
would be a little light on the power output for
a pair of 813's running full tilt.

Its always a good idea to have plenty of extra 
audio power, running it light makes it clean.

My 813 rig runs a pair of 4x150a/4cx250b tubes as
modulators, 600 watts of audio in class ab1.

 So the rf deck runs 800 watts input or there
abouts, and I have 600 watts of audio to modulate it
with, at 2000 volts on both.

There is no big difference in voltage between the mod iron
primary and secondary, the impedance ratio is not
extreme, and the audio is clean.

My favorite setup is triodes in push pull as an RF
deck, modulated by something in ab1.

A pair of 812a's or 811a's work well for the rf deck,
and they work well as modulators, even if class b,
if driven with a backwards 5000 to 8 ohm transformer
and some modern audio stuff.
At 1500 volts, you get about 300 watts out easy.

The 813's in RF service seem to modulate real well for multi grid
tubes, are real rugged, last a long time, and 
(used to be) cheap.

People use them as modulators as well, but I am
not sure how clean they are, they run class ab1, 
or you can triode connect them I think and run them in
class B.

People run low power on 40 meters all the time,
but I would not get on 80 without a strong


> -----Original Message-----
> From: amradio-bounces at mailman.qth.net 
> [mailto:amradio-bounces at mailman.qth.net] On Behalf Of Jack Schmidling
> Sent: Friday, November 10, 2006 11:21 PM
> To: Discussion of AM Radio in the Amateur Service
> Subject: [AMRadio] 813/811 Rig
> I am looking for an 813/811 rig or parts to build one.
> Open to ideas.
> js
> -- 
> PHOTO OF THE WEEK: http://schmidling.com/pow.htm
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