Newest addition to my station

[Hawkeye351]

You are looking at the last big amp Screwdriver (here in NC) ever built due to his health has left him unable to do it anymore.

Turbo Smasher
1 tube - 3CX400A
Max input key - 50w
Max input swing - 50w
Max output key - 500w
Max output swing - 1700w
Large squirrel fan

 

[gamegetter]

nice,
might you have picture of the 3cx400A and the circuitry around it?

 

[Hawkeye351]

No schematic, but I will take covers off this weekend and post some pics of the inside if you like.

 

[nomadradio]

Three see-ecks four hundred?

Cool choice. Has a lot of power gain for a triode. Probably also has the number 8874 on it. Be nice to it, they've been discontinued for a while.

73

 

[ClaimJumper]

I would take the knobs off and clean up the faceplate and Purdy the whole thing up again. Very nice score! Love that eagle too!

 

[Hawkeye351]

Someone told me the 3CX400A would not handle much more than a 3 to 4 watt unmodulated carrier for input. From what I've read, it will handle from 9 to 15 watts unmodulated carrier input, claim being 12 watt unmodulated carrier input being the sweet spot. The guy I got it from ran a 30 watt unmodulated carrier input into it. So, I ran it with my Saturn with RF power wide open (unmodulated carrier at 12 watts exactly) swinging 50w PEP and it ran beautifully. What am I missing here?

 

[nomadradio]

3CX400A would not handle much more than a 3 to 4 watt unmodulated carrier

Could it be confusion between the four-see-ecks four hundred tube and your tube? The "four" is a tetrode. The drive requirements are scandalously small. The "three" is a so-called power-grid tube. The data sheet says the grid's power rating it 5 Watts. That's average power. That tube has a power gain of over 20 to 1. You shouldn't need more than 50 Watt peaks or 12 to 15 Watts average drive power to get around a thousand Watts peak output. This tube is designed to 'steal' as little of your drive power as possible to heat up the grid wires.

Naturally the choice of anode voltage has a big bearing on this. And it's hard to measure just how many Watts of stress you're putting onto the control grid. 11-meter amplifiers tend to be built as race cars. They last a lot longer at 2/3 or half throttle.

73