another Tube question, tube testers, are they all the same?

[faster100]

http://cgi.ebay.com/ws/eBayISAPI.dll...828358187&rd=1

will this tester test St70 tubes?? are they all compatable? I'm trying to learn a bunch all at once here... bare with me.

or what should i look for on the cheap?>

[organ]

I pretty much don't know about tube testers but if you decide to get one, make sure you have a shop calibrate it for you.

You can tell when a tube is getting weak. It will sound weak, less sparkle, etc.

Maurice

[mhardy6647]

Nope, not all the same. There are two issues:

1) compatibility with the tubes you want to test. Not sure which "ST-70" you're asking about, but both the Dynaco ST-70 and the EICO ST-70 are 'modern' designs as tube amps go and virtually any modern (i.e., 1960 and later) tester will accommodate the tubes. Sometimes it's more of a problem for 'vintage' amp designs, as the later tube testers won't e.g., accommodate 4-pin tubes like a 45 or a 2A3. I have this problem with my mid-60' Sencore "Mighty-Mite" tester. "Old" testers won't accommodate newer pin layouts (e.g., "compactron" types).

2) Most cheap tube testers only test for emission, grid leakage and shorts (like my "Mighty Mite"). The best testers will also test "transconductance" which actually tests the performance of the tube with a load on it. The Hickock TV-7 is a classic example. Testers that will test tube transconductance are much preferable IMO.

If you buy a tester, make sure you get (or can get) a setup chart for it that includes the tubes you want to test.

Hope this is helpful.

[faster100]

hey thanks, you bet... So what about the heathkit testers?? I have seen several, IT17, 25 and Tc-2


My amp is a Dynakit stereo 70

[mhardy6647]

I unfortunately don't know off the top of my head, but probably some or all do. Search for information on these specific testers with Google and look for words like "mutual conductance" or "transconductance" or "mu".

You can check for manuals for these testers at:
http://bama.sbc.edu/

Other good sites for Heathkit info:
http://www.heathkit-museum.com/
http://www.qsl.net/kb7rgg/heath/heathkit.html