Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => AmpTools/Tech Tips => Topic started by: eleventeen on September 27, 2016, 10:36:57 am
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A guy locally is selling a Tek 575 transistor curve tracer for $40. It's in B- condition; it has some tubes taken out of it, but those are tubes I have, generally, and are not exotic at all. Let's assume it can be fixed.
Early 575's could apply 100 volts to a TUT (Transistor under test)
Later ones, 200 volts.
Could not such a beast be jiggered in such a way to test a 12AX7 (or any 12A_7) to produce an actual trace of load lines?
Would that not be exciting?
Besides winter approaches and I could use a room heater.
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Primary question is: how high can the Collector (Plate) voltage go? (Ah, I see you answer that.)
And do you really need to take curves on well-documented devices? What can you learn that you could not work out by looking at GE RCA and Tung-Sol curves? (Which are often copied from each other, actually the EIA registration.)
The price is total non-issue.
EDIT A tube-dude I know says "I do all my tracing at home on my 575". He was working with some odd rare Russian types. He later got two tired 576 from work. If you are really digging this, I can put you in touch, but his life has been busy.
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Well, the idea would be, this is or could be the world's most comprehensive tube tester. Of course, you'd have to develop your own calibration against the graticule on the screen. OK; compare against some collection of brand new or known super-condition 12AX7 etc; Light up the tube, photograph the screen with lit graticule.
Imagine you are a seller of used tubes. You buy gear and acquire such tubes in qty. Way more than you will ever need or use. You can invest in (and I have) a Hickock or other Gm and Mu tube tester, but whatever readings you come up with are phenomenally sensitive relative to how accurately you've set your line voltage, and besides, it's your word against whatever. You can say anything you want about any particular used tube and offer a guarantee should you wish, but a dissatisfied buyer still has to send the thing back to you; while they trash your reputation as a seller.
When I was offering matched pairs of tubes, I made that thingy that applied equal B+ & bias to a pair of tubes and simul-displayed the two plate currents on two identical meters. IMO that built a lot of credibility. Most "matched pairs" you see on ebay have the same date codes. Well, that ain't matched, we know that.
(http://i172.photobucket.com/albums/w32/ttm4/ebay_tubes_4007.jpg) (http://s172.photobucket.com/user/ttm4/media/ebay_tubes_4007.jpg.html)
The ultimate idea is to generate cred as a tube seller. For my purposes, I am happy with my Hickock and a sticky label with a number. That's what everybody else has.
As for actual transistor traces..? It's not like I do any great amount of transistor work, but as far as I'm concerned, until one is way up in the megahertz you got yer 2N3904/2N3906, 2N2219, 2N2222, 2N2905, 2N3053, TIP41/42, and 2N3055 and that just about covers the waterfront.