[AMRadio] 3-500Z 's as a modulator?

Albert Santangelo ve3ajm at sympatico.ca
Sat May 29 06:24:07 EDT 2004

I use a pair of them in my TMC GPT 750 as modulators with 3kv on the

They work very well, and are easy to drive. I use a simple zener diode
scheme in the filament transformer centre tap ground return for biasing
the tubes to idle at about 50 ma per tube.

The tubes/sockets are relatively inexpensive for their capabilities, and
available new sources like RF Parts on the net.

73  Al Santangelo  VE3 AJM

Patrick Jankowiak wrote:

> After buying several 304TH's and 304TL's, and out of five,
> finding only one to be good, I'm pretty sick of it. I don't know
> why I seem to end up with all the duds, but it's pretty frustrating.
> -one had half the filament out
> -two had a filament to grid short
> -one flashes over at 500V plate voltage
> I am thinking about the 3-500Z as a modulator. Any comments from
> the wisdom here?
> At least I can buy them new and they will have a warranty.
> I suppose sockets, anode dissipators, chimneys, and chimney
> hardware can't go bad, so I can't really get ripped off there..
> Does anyone have a couple sets of 3-500Z socket/chimney/hardware
> they'd be willing to sell?
> Looking for:
> -two SK410 / SK410S or equivalent air system sockets
> -two HR-6 (0.6" tall) heat dissipating connectors
> -two SK406 chimneys and clips for the chimneys
> -Pamotor 2000 or 6500 or equivalent blower that will do 13CFM at
> 0.1" pressure or better
> I also have a commercial RF deck with six extremely good 4CX250B
> tubes and blower (it's actually a puse amp) I would trade, for
> the above and a -guaranteed very good pair- of 3-500Z's.
> Thanks,
> Patrick
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