• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

why does KT66 have a greedy heater ?

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#21
sser2 said:
....some tubes (although not exactly 6L6 family) without top cap are rated high voltage, like 800 V EL34 and EL37, or 600 V 6550. But no manufacturer has the guts to use these capabilities. ....
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Ampeg VT-40 family ran 7027 (or 6550 factory option) at 590V idle B+.

There's two generations. Early ones ran the Screens nearly as high as the Plates. A later run puts Screens at a more sensible 338V.

UniVox 1221 ran 6L6GC at 660V Plates 330V Screens. I had a larger model with six(!) bottles at similar voltage (maybe lower?) and it was reliable.

Bogen made a few 150W+150W four-8417 commercial amps running around 600V supply, 300V on Screens. Reasonably solid beasts. The ones I had were worked hard to run film projectors at 59.9Hz. One caught fire and they were discarded (to me). Turned out the burnt channel had one solder joint that had never been soldered, holding on by the crimp, which apparently let go. At the time I could still get satisfactory 8417 and I used them for years in PA work.
 
#22
Hi PRR,
And I think that running 6L6 tubes with 475 V plates was bad (Fender Twin series). Not very many new 6L6's will survive that.

I've run across a few unsoldered connections as well. They usually burn the wire badly enough so it won't accept solder unless you really work on it.

-Chris
 
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