The Steel Guitar Forum

I`m gonna try to get a tube tester off Ebay but it seeems like there`s a lot of different models there.

I want to check out my preamp tubes (12ax7/at7 - (I think)) some KT88s and also what goes in to a fender twin.

Are there some tubes that the old tube testers don`t cover?

Any help greatly appreciated.

Thanks,
Dag<FONT SIZE=1 COLOR="#8e236b"><p align=CENTER>[This message was edited by Dag Wolf on 18 May 2003 at 06:24 PM.]</p></FONT>

Dag,
There are certainly a lot of tube testers on e Bay.
If you want to seriously test tubes you should try to get either a Hickock Dynamic Mutual Conductance Checker or a Military Surplus TV-7.
There is a Hickock Model 750 on there as well as some 539's and 600A.
Stay away from the "filament checkers" you can do that with an ohm meter.
Most of the others only check for shorts and emission.
No checker will tell you how the tubes will perform in an actual circuit.
To check for noise and microphonics in a pre amp tube, you need to be able to plug in a pair of headphones. I think the Hickocks will allow you to do this. (Although it's been a long time since I used one.)
In the RCA Tube Manual (there are several editions, I'm quoting from an RC-22)
there is a chapter on testing tubes.
In the last paragraph on "Tube Tester Limitations" it states:

"The tube tester, therefore, can not be looked upon as a final authority in determining whether or not a tube is always satisfactory. Actual operating test in the equipment in which the tube is to be used will give the best possible indication of a tube's worth."

Blake

Thanks for the response.

So will a tester tell me if a tube are bad or good - but it can`t tell for surtain if it will perform 100% in the circut?

Thanks,
Dag

Dag,
Yes ... sort of !

A tube-tester will tell you whether or not a given tube works AT ALL - usually by testing it at a voltage MUCH lower than the voltage in any guitar amp - and some of them will give you a more-or-less meningless figure/percentage of "useability" but, like Blake so correctly stated, it won't tell you how it will perform - much less how it will sound - in an actual guitar-amp circuit.

You can use a tube tester to see if a given tube is worth testing for real IN AN AMP.

IMHO of course !

Ole

A mutual condutance-type tester will also give you a better idea of the gain of the tube, which is important when matching pairs, or sets of tubes. As stated, although a good tester will test the tube at approximate operating conditions, no tester made will "load" the tube like it gets loaded in an amp. "Plug-and-play" is still the ultimate test. Get a tester made in the late '60s (or later), and it'll check just about any tube you will come across.

Thanks for the inputs

It has been most helpful.

I`ve concluded not to buy but go for the simple solution:
Buy a brand new matched set of tubes and plug it in. If the old ones perform good compared to the new set - then simply put the old ones back and play them till they wear so much that the old ones need replacement.
Should be easy to trust my ears and also I will have a replacement on hand!

Thanks,
Dag
<FONT SIZE=1 COLOR="#8e236b"><p align=CENTER>[This message was edited by Dag Wolf on 21 May 2003 at 09:35 PM.]</p></FONT>

I carry an extra 12AX7A in my bag of tricks and it's come in handy more than a few times!

Bob M.

I would go for the Hickok 539C which will cost more but when you resell I'm sure you would at least get your money back. Dont forget to ask if it works right. Also the meter movement needs to work flawlessly so ask about it. It would be tough to replace the meter movement.

If you want a new unit you might check out the vacuum tube valley website --- as I recall they offer a new checker there. You would have to convince yourself that it would work for your application.

Rick

Your idea to buy an extra set of tubes is the absolute best idea, especially if you're only conderned about a Fender "Twin" I just sold two Twins that I'd had for thirty five years and they seldom needed anything. That set of tubes will last you a liftime. Plus, like they said . the tester isn't going to tell you very much that you didn't already know.
Jim