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Old 29th June 2008, 07:53 PM   #1
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Location: Dallas
Default Calibrating an emission tester

I have a SICO Model TW-11, it seems to work (mostly).
Certain levers have tricky spots, but all work if jiggled.

Anyways, I'm going through a boatload of 6DJ8's that
my father found in his stash. Pulls from Tektronix and
HP scopes. Score or more of Amperex, half dozen or so
Sylvania (only two Sylvanias had clear markings left on
the glass, others identified by internal construction),
and four precious Telefunkies...

My NOS "bogie", and RCA 6DJ8 turned out to be just
another Sylvania of unknown prior usage stuck in the
wrong box... So I got nothin I can depend on to tell
me how a truly new old stock 6DJ8 should measure?

My meter consistantly rates ALL these tubes at the
bare low end of the green, just above the "50" mark.
Except the Telefunkens which measure about "60",
but still quite low in the green. The meter goes to
100. Anything below 40 is "RED" or "FAIL". From 40
to 50 is a white area marked with a "?".

I have my plate load set at "30", consistant with a
12A(U,T,X,Y,Z)7. There are no 6DJ8, 12DJ8, nor 6922
on my scroll or in my booklet, so I am just fudgin it.
This might be the wrong plate load for a 6DJ8???
The "load" dial seems to be a smooth turning pot
or perhaps a variac, it has no detents.

I have the filament set for 6.3V on pin 5. SICO says
I am supposed to power filament on pin 4, but thats
(no coincidence I am sure) one of the trickiest spots
in all of the levers. So I burn the filament from the
other end of the candle. Does it matter? I doubt it...
The filament dial definitely has detents.

Anyways, I've NEVER seen any kind of tube of any
model measure any better than "60" on this meter.
The SICO meter itself might be out of calibration.

Tweaking the flathead screw at the fulcrum of the
needle lets me add or subtract about 10 from the
reading. Right or wrong, I've set the screw and the
live needle reading back precisely where I originally
found them.

May have a pair of JAN Phillips 12AT7WC's that I am
pretty sure never been fired up. Can I use them as
bogies? What should I be looking for the needle to
read with a "new" tube? How green is green enough?
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Old 29th June 2008, 08:31 PM   #2
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I just went through a batch of Jan 12AT7 tubes and i found the readings were all over the place. One was shorted right out of the box. most were fairly reasonable and one had a severe imbalance between sections.

There are a couple of websites Like www.alltubetesters.com and the radiola guy http://www.radiolaguy.com/misc.htm#6L6 that sell known bogey tubes.

Roger Kennedy at All Tube Testers will bogey a tube for you! you can either send him the tube or tell him which tube you want and he will select one and send it to you with known values.

Without having a known value or a known method of calibrating your tester...who knows what your actually seeing on that meter?


Zc

P.S. have you been to the First Saturday sidewalk swap meet there in Dallas yet?? I used to live there and i was at those meets EVERY month!
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Old 29th June 2008, 08:33 PM   #3
kevinkr is offline kevinkr  United States
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IMO Emission testers are all but useless for tube testing and grading. Do not waste your time testing lots of tubes in this tester. Instead look on eBay for a tester that measures the tube's transconductance - one of the true measures of tube merit.

Appropriate testers will indicate that they are mutual conductance or transconductance testers. IIRC There are some Sylvania testers that can be had cheaply that measure both transconductance and emission combined into a single measurement, and are quite useful if not ideal. (You won't be able to compare readings to other known reliable testers.)

Hickok, Sencore and AVO make some good transconductance type testers. Personally I swear by a Hickok 539B..
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Old 29th June 2008, 10:32 PM   #4
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Quote:
Originally posted by Zero Cool
P.S. have you been to the First Saturday sidewalk swap meet there in Dallas yet?? I used to live there and i was at those meets EVERY month!
There is a "big" one on the 1st Saturday, and a little one the 3rd.
Grown up out of the Heathkit Store's "Sidewalk Sale". Neither day
is of the scope or scale that you may have seen many years ago.
But it still exists, and refuses to die.

I rarely see more than two guys bring anything with tubes in it.
Though I did find and buy a Hammond M3 organ there for a friend.

Cell phones and internet squeezing out HAM Radio, vanishing mom
n-pop TV repair shops and computer stores. The rise of disposable
unserviceable electronics of all kinds really took a toll on attendance
and the quality of surplus available.

If you want a used Dell computer, it would still be the place to go.
Otherwise you might be dissapointed.
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Old 29th June 2008, 11:36 PM   #5
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Join Date: Nov 2007
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Just ran outa tube boxes... Shoulda got more at HamCon, but
who knew I would be handed this big a stash out of the blue?
Was assumed that I already had every tube my father had
ever saved but now wanted to ditch. But then he goes and
finds MORE... No rest for the wicked!

Anyways, the highest in emission so far seem to be a pair of
"Hewlett Packard by Amperex". I don't know if that makes em
better than the Telefunkens or not. As I am not set to measure
any factor of quality aside from emissions right now...

On a good note, none of these have tested "BAD" or refused
to light up. I still have about 20 more to go through. And then
on to all the oddball tubes that are NOT 6DJ8's.

Got lots more 6U8A, 6AU6, 5654, 5651, and some HV diodes
with plate caps (yes, he saved the caps!)...

How does one test OA2 and OB2 regulator tubes?
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Old 30th June 2008, 04:56 PM   #6
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by kenpeter
J<snip>
How does one test OA2 and OB2 regulator tubes?

I take it your tube tester does not list these types in the scroll chart or manual. Most lab testers will test these and some old emission types do too..

They are not too hard to test provide you have some reasonable value power resistors on hand and a lab supply to use as a source. Look up the specifications for the type you want to test, set the supply voltage to the lowest value listed for starting voltage and select a resistor that allows a current of 10 - 15mA when the tube has started. Turn on supply and measure the voltage across the tube, if it meets the spec you have a good tube.

Here is a link to a comprehensive data sheet (Raytheon): http://www.mif.pg.gda.pl/homepages/f...38/0/0A2WA.pdf

This French language data sheet is more useful and even shows typical application and test circuit - should give you an idea as to what is required here: http://www.mif.pg.gda.pl/homepages/f...20/0/0A2WA.pdf

(Some of the Mazda/Belvu/Cifte data sheets are really excellent if you have a working knowledge of French.)
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