On Apr 18, 8:44*pm, "Arfa Daily" wrote:
It was a fairly 'new' tube as in 8 years or so, but an original Marshall
factory fit.

By new production I meant anything Russian, China, etc. made these
days since tube production started shutting down in the 70s. The
Slovak made "JJ" branded pwr tubes are very robust. I'll normally use
them unless a customer specifies otherwise.


As far as you could see looking through the glass, it was a
'genuine' EL34 pentode, rather than a 6L6 look-alike beam tetrode
masquerading as an EL34.

That would be a 6CA7. Some ppl prefer the 6CA7 to EL34s in Mar$halls.
They're less "furry" sounding, kinda like a KT88's younger sibling.
Original Sylvania 6CA7s can bring impressive money these days for NOS.


The screen grid connection ribbon looked intact.
Just for sport, I tried measuring the capacitance from the screen grid to
the anode, and it measured exactly the same as on the opposite tube which
was working, so that would indicate that the screen was in fact intact.
Never-the-less, the bad tube drew no discernible screen current at all. The
emission was pretty poor on both tubes, so about the only other thing that I
can come up with is that the emission was so low on that tube, that the
standing bias had it basically cut off, so the screen had no source of
current to draw from.

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