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Tube choice for 600R output transformer

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kodabmx

kodabmx

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Joined 2011
For good results, you'd need at least 8 per channel. Otherwise you could use 4 6KG6 sweep tubes per channel, connected as triodes, idle at 120ma per tube, B+ 300V. This will make about 15W class A limit, 140W total. 6C33C could also work, but they aren't very linear, hard to drive, and power hungry.
 
kodabmx

kodabmx

Member
Joined 2011
EL509 would work. As far as your driver I'm not sure. Someone else hopefully will weigh in, however, here's the driver I use, personally.

Cheers.
Koda
 

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PRR

PRR

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Joined 2003
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Tubenstein said:
... primary 600 ohm plate to plate and capable >200W power....
Click to expand...

200W at 600 Ohms is 346V RMS. 173Vrms each side. 243V at 1.61 Amps peak each side.

We want a tube(s) with much less than 243V drop at 1.6 Amps.

A couple of the big H-sweep tubes can do this, but may not make the dissipation needed for non-switching audio.

If we would like good efficiency we sure can't have peak tube drop even 20% of signal swing, under 50V. 50V/1.6A says 30 Ohms diode line.

A good tube amp can do 60% efficiency. I suspect this super-low impedance will not ge there, but pretend/hope. We need 133 Watts dissipation, 67W per side. Since the bigger common tubes go to 30W-40W we need at least 2 per side.

42KN6 will do 0.8A at 60V. So two/side makes 1.6A at 60V drop, 300V supply. Huh. A thumb-count of watts lost suggests 29W/jug, which fits the 30W rating. To me it seems quite on-the-edge, and I'd lean to 6 bottles.

Plate power is like 300V @ 0.8A. G2 should be near 125V (pending experimentation) and may vary 20mA to 100mA.

EL/PL509 is also in the running.
 
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kodabmx

kodabmx

Member
Joined 2011
OTOH, The plate structure in at least the 6P45S (larger than the 36LW6 by a margin) is roughly the same size and weight of a KT120 which is rated for 60W but has a lower powered heater. YMMV, but in sweep tube duty these tubes ran for years. I have a very discoloured, well used 6KG6 that I added to the amp to test. It's still working fine after all these years. Don't judge a tube by it's glass colourings :)

I feel these tubes are for us amp builders, tubes on steroids. If you push them they make a LOT of power. Ask George, right? If you run them sanely*, they will last for years.

*sanely in this case means about 100% of the datasheet spec... I run mine in triode at 35W idle.
 
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