[AMRadio] 813 question

Brett gazdzinski brett.gazdzinski at verizonbusiness.com
Tue Jan 31 18:56:35 EST 2006

My latest rig is a pair of 4D32 tubes, since I got 4 new ones at $20.00
each. I have run them at 1000 volts, and 1200, even tried 1500 volts,
they give about 300 watts out at 1200 volts...

My normal rig is a pair of 812A's, most were $5.00 at fests,
and I get 300 watts out of them at 1500 volts, no color on the plates.

Some of the 813's I have I got out of homebrew amps I got at fests,
$25.00 for the entire thing.(it looked really nasty)

The 813's have to be king though, 2000 or 2200 volts, and 
600 watts out is easy, they seem to modulate well with a choke
and a big dropping resistor from a low voltage supply for the screens.
I use a screen protection circuit in all the screen grid tubes,
which may be why they last.

I have a blower that pulls air in from a filter and blows it out 
around the bases of the tubes, in case I want to push things.

Great working tubes, a lot of bang for the buck, and I like the 
lower voltage they can run at, you can do 1000 volts, 1500, or 2000 or even
2500 volts!

> Brett,
> Those 813's are practically indestructable --- and I should know, too,
> having used them in my amplifier for some 16 years now (only 
> had to replace
> the tubes ONCE!...and we're talking surplus/Hamfest jugs here, too)...
> I have examples here of BOTH the graphite AND metal plates 
> --- NO IDEA how
> the metal plate versions retained the same "813" number --- it CAN'T
> possibly be the same tube! --- but it has.
> I have yet to use the metal ones, though...
> Never could understand why guys spend the big $$$ for tubes --- albeit
> modern, low drive, efficient ones --- when rugged, bargain 
> basement bottles
> like the 813 still abound...
> ~73~ Eddy VE3CUI - VE3XZ

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