[Amps] la-1000 what to convert to?

[Will Matney]

Chuck,

Why not convert it to run on four 6KG6A (EL-519) tubes? There's replacement boards available from FAR Circuits if I recall. To be honest though, they ran those four 6LQ6 tubes a little too hot at that anode voltage. A better voltage is at 900 Vdc. I guess they were thinking squeeze all you can get out of the four but the tube life isn't as good. A couple of 6KG6A's will do approximately 275 watts PEP so four should get you 550. I built several grid driven units using these and that's about what I could get without the anode cherrying up. That's something else to keep in mind also. A sweep tube does not act like a broadcasting tube where the anode can get red hot. A sweep tube will start to fail considerably after the anode starts to get red one time. Adjust the drive for full output from the amp with the bias backed off to about -100 Vdc. I used the bias as a hi/lo circuit varying it from about -100 to -150 Vdc with a variable supply. The EL-519 tubes are about $15 to $20 each now I think.

For any interested in building one of these that is grid drive, below if the following approximate circuit voltages I used;

Anode voltage: +900 Vdc @ 1 amp
Screen voltage: +450 Vdc (from center of plate voltage doubler)
Control voltage: -100 to -150 Vdc (250 mA)
Heater voltage: 6 Vac @ 2 amps each

Best,

Will


*********** REPLY SEPARATOR  ***********

On 6/5/06 at 9:37 AM Partain, Chuck wrote:

>I have a orig la-1000 amp supply laying about and figure for this winter,
>that might be a good project to tear into. 
>Parts collection will start soon. I see a few folks have converted to
>ceramic tubes, russian glass or whatnot.
>anyone do any of these? and what might you suggest is best?
>
>on a REALLY good day I can see ~500w out of the  4 sweeps!!!
>
>1100v at 1 amp I THINK the transformer will do, I don't want to replace it
>yet.
>
>
>ka1mwp
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