[Boatanchors] Tetroded as Triodes

Bry Carling bcarling at cfl.rr.com
Sun Feb 19 15:08:03 EST 2012

Hi Wilson,

I have had some experience with a homebrew amp using two 4-400As that was similar.

It sure sounds like you need more loading capacitance, and you REALLY need a plate 
current meter to keep that baby dipped properly and protect your valuable 4-125A valves.

73 - Bry, AF4K

On 19 Feb 2012 at 13:26, Wilson Lamb wrote:

From:           	"Wilson Lamb" <infomet at embarqmail.com>

> 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
> output.
> 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.
> Thanks,
> Wilson
> W4BOH 
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