[Boatanchors] Tetroded as Triodes
anchor at ec.rr.com
Sun Feb 19 15:11:20 EST 2012
Sounds like you've made great progress, from something you bought as a
source of parts ;-) Sorry I can't provide any thoughts on your output
question, but I hope that not too much of that cathode current is grid
current, I'd think less than 50ma?
"There is nothing -- absolutely nothing -- half so much
worth doing as simply messing about in boats"
Ratty, to Mole
On 2/19/2012 1:26 PM, Wilson Lamb wrote:
> I acquired an amp with a pair of 4-125As in grounded grid. It was a
> mess, never finished, and took a LOT of work, but is now on the air.
> Does anyone have experience with this setup? There's plenty of plate
> voltage, 2700 and off resonance the tubes will go bright red. Max output
> is 300W, however, which I think is low. There's no plate current meter
> yet, but cathode current at max output is about 300mA, much of which is
> grid current, I think. Key down CW at 300W out shows almost no color in
> the plates and increasing loading with the pi net output produces less
> It sounds great on SSB and has a lot of gain (15W drive for 300W out).
> So what's happening that keeps it from producing more output when the
> drive is raised?
> I've seen some articles on 4-400s in GG, but never the little 4-125A.
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