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Vacuum Tubes for Amps
Making Tubes
"Teleologist"
>Interesting thought about temperature - hadn't considered that. I also
>realize the same tube from the same plant on different weeks can sound
>slightly different, but I'm just one of those people who likes looking at
>tubes & trying to figure out what might make them sound the way they do. :)
Me too. I spent a whole day going over the ex-GE works
after glass tube production shut down
(they let me have the run of the place,
which was quite a treat), asking questions & so forth.
One of the telling comments came from the ex-shop foreman,
who noted that "making tubes is an art". Even with personnel that
averaged 15 years experience, on a *good* day, 10% of the run was
NFG and had to be chucked. No lie, I saw 55 gallon drums full of
dud 6550A's.
OK, I would attribute the differences between Philips ECG
6L6-WGB and 7581A/6L6-GC to the following:
1.More heat concentrated in a smaller bulb. More heat means more
control-grid current, thus hotter tubes would start clipping at the
grid than cooler ones would.
The fact that the later model Philips 6L6-WG/5881 didn't
have grid cooling fins (which, IMHO, they should have had),
I attribute to one thing : Philips mgmt did exactly what they
had to, & no more. Some of the stuff the *military* actually
type accepted and spent US tax dollars for, was truly bizarre.
2. The specs that 5881/6L6-WGB had to pass to be type-accepted
weren't as tough as those for 6L6-GC/7581A.
>BTW I also have some GE WGBs from the 70s - these have a fatter/taller
>bottle(but not as tall as the Phillips 6L6GC) & use a larger diameter base
>than the Phillips WGBs. Internal structures are quite different & they
>sound much different. They're my personal favorites for Tweed Bassmans.
BTW, if you've ever seen Tungsol 6L6-GC...they look like a GE 6L6-GC
in a Sylvania bottle!
Your comment about the sound of tubes changing from one
production week to the next, is not without foundation.
Cathode coating is a suspension, not a compound, and
the skill of the folks mixing & applying the stuff is very
important.
Two anecdotes:
(1) AT&T/Western Electric wanted to get out of the tube biz in the
1980's (they quit in 1988). They tried to job the tube production
out to another company, Cetron. Despite Cetron's efforts, they could
not produce tubes (300B's) that would pass WE spec for plate current.
The only known reason was Cetron's problems with mixing &
applying cathode coating.
(2) When the Chinese tried making 6550's & KT88's
(BTW, no coincidence that they look like Tungsols),
their skill at doing cathode coating was so bad that
there were a number of failures where the coating
actually peeled off during use & touched the
control grid. Some of the failures were truly spectacular.
Ned Carlson, Triode Electronics, Chicago, IL http://www.triodeel.com
Open 12:30-8 PM CT, 12:30-5 PM CT Sat Closed Wed
ph:773-871-7459 fax 773-871-7938 "where da tubes are"
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