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kellys_eye
Posted: March 12, 2012 08:58 pm
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nearly (possibly ALL) my tubes suffer from logo erasure. I'm sure this is quite common?

But what do YOU do to identify the tubes? I was thinking 'typing correction pen'. Maybe there's a technique to 'spray' some protective covering? dunno.gif


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Colt45
Posted: March 12, 2012 10:02 pm
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a fair amount i can tell by looking at them.

if you have west-euro (incl. limey) tubes, they usually have a 3 digit code etched near the base - you can crossref this to the model, and factory.

I've heard throwing them in the freezer to get some condensation helps, never tried it myself.


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CWB
Posted: March 13, 2012 01:53 am
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yep ... cool the tube a bit and the breathe on it .
many times the numbers will show up (angle of view and lighting are experimental) .

a spray coating (or anything that will break down with heat) will cause problems with high envelope temperatures .
i have seen a carbonized thumb print on a horizontal output tube absorb enough heat to actually soften the glass and cause it to suck in .
the glass was about 1/8 inch from the plate before it let go .

high powered/temp tubes (say 4-400 or 4-1000) need to be "wiped down" after installation before firing them up .
that's why i always carried a bottle of rubbing alcohol in the truck or kept one in the transmitter shacks .
the factory instruction sheet that comes with the tubes explains the reasons why .
you can find these sheets on line by using the appropriate google search for eimac tubes .

for marking tubes , scribing the numbers in the bakelite base works well .
for tubes without a "base" ... box them up and label the box .

low temp tubes can be marked with a "magic marker" near the bottom of the tube .


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tekwiz
Posted: March 13, 2012 09:12 pm
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QUOTE (CWB @ March 12, 2012 04:53 pm)

high powered/temp tubes (say 4-400 or 4-1000) need to be "wiped down" after installation before firing them up .
that's why i always carried a bottle of rubbing alcohol in the truck or kept one in the transmitter shacks .
the factory instruction sheet that comes with the tubes explains the reasons why .
you can find these sheets on line by using the appropriate google search for eimac tubes .


You mean hipo toobs like these ones?

user posted image

user posted image

cool.gif


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Nothing40
Posted: March 14, 2012 01:11 am
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Also,sometimes digital cameras can pick out bits of the logo that are hard to see..Maybe take a couple pictures,and see if anything shows up. dunno.gif

Short of that,Some educated guessing might narrow it down. What does the plate structure look like,what kind of base does it have,which pins are connected to which internal elements,is there a top-cap,etc.
Usually that's enough to at least tell you what type/family of tube it is.


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CWB
Posted: March 14, 2012 12:43 pm
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one would be hard pressed to visually tell the difference between a 12AX7 and a 12AT7 .

oddly enough , the 4-400 and the 5-500 look identical .
the filament voltage/current being different (sans plate dissipation) ...
as well as the price ! gawd , the last 5-500s i priced were about $450.00 each .

the price difference for four of them was enough to make it economically realistic to change a transmitter over to the 4-400s .
after the changeover and adjustments , the transmitter met factory spec by my equipment .
the FCC field guy came by for an inspection (prearranged) and examined the changes in the rf and af decks , etc .
he and myself went through the tests *again* with his test equipment (real deep pocket stuff) .
he gave it the thumbs up and a little sticker .
he mentioned that several engineers were switching over to the 4-400s and he had received many questions about this modification .



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Sch3mat1c
Posted: March 14, 2012 06:19 pm
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You're gettin' rusty, CWB... 12AT7 is the one with the wrap around looking plates that come to one seam. smile.gif AX and AU are a challenge though... if you're lucky, you can peek at the grid through a pinhole and make some deductions!

Most 6SN7s were made with a boxy, single seam anode, too, but a few (GTB models mostly I think?) were made with "big AU7" style, embossed, two piece plates. And I think 6S4 was similarly an overgrown 6C4.

Tim


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Village Idiot
Posted: March 14, 2012 09:21 pm
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CWB
Posted: March 15, 2012 02:19 pm
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yep tim , yer right about the AT, AX and AU ...
must be these damnable antihistamine pills i am taking .

as i recall , there was an industrial/jan western electric tube that looked like a 6C4 but it was no where close .
http://www.jogis-roehrenbude.de/Roehren-Ge...den/6C4/6C4.pdf

man , years ago a lot of those were used in uhf converters .
the old AN/PRC25 used one of them in the final ... of course it was the JAN flavor .

ps ... check out the home page of that pdf link ... some neat stuff .


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Sch3mat1c
Posted: March 15, 2012 04:20 pm
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Did you see his tube clock? No...seriously! ohmy.gif

Tim


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Colt45
Posted: March 15, 2012 09:31 pm
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His tubeclock is cheating - there's some SShite in it :-pppppp


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CWB
Posted: March 16, 2012 02:45 pm
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hmmm ... a little research ... there is not a lot of "real" info about the development phase of the '25 .
according to the "deep details" available , the 6C4 was used in the early prototypes (and some limited production) of the '25 but abandoned in favor of the 2DF4 (good choice ... rugged as hell and very robust) .
http://www.nj7p.org/Tube4.php?tube=2DF4

of all the '25s and 77s i have seen/cracked open , only one had a bad final ... the filament was open .


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