Building a tube matcher

[FYL]

That I get, but I would also like to be able to test how much life is left in a pulled tube so I know it wont die on me 10 minutes after I get it home.

End of life tests are quite easy : measure the tube with normal params, then lower heater voltage by 10% and measure again. If the results are the same or nearly so, the DUT has plenty of life left.

[selloutrr]

a used maxi matcher for under $500 will match and give estimated life but it is power tubes only. You might not think you need lab quality results but if you don't have enough voltage to test the tube at operating voltages that tube amps run at your readings aren't going to matter one bit because that extra voltage can cause a tube to behave completely different. i.e. a tube that tests good at 250volts could fail at 400volts.

[jcr1234]

Ok, so how do I test pre amp and power tubes at the proper voltages?

[Structo]

In an amplifier?

[Phil_S]

In an amplifier?

Interesting proposition. I imagine the decade box is your friend here. Use it to swap cathode resistors. That changes the bias point. You can get several readings for current draw (voltage drop across the resistor). Plate voltage will change as you swap Rk. It will let you graph results and calculate Gm. What do you think?

[selloutrr]

if you want an external dedicated tester that will test preamp and output tubes at tube amp operating voltages your choices are quickly limited to expensive testers $2k and up. Such as the Vacu-Trace, Amplitrex, and Computer controlled card-o-matic by hickok w/ the increased power tranformers.

some of the old hickok tube testers will also work but they are sought after by hifi collectors and will most likely need a full restoration service and calibration as well as new data roll.

sorry i don't have a cheap and easy fix.

[selloutrr]

I was logging in to check my email at vintage amp forum (don't get butt hurt this forum is the best!) I ran across this article

http://vintageamps.com/what-does-%e2%80 ... /#more-458

[PlinytheWelder]

I have 2 of these tube regulated power supplies, I suppose that I could kluge together something to match output tubes with them....

[img835]http://verosurfcam.com/IP-2717.jpg[/img]

[Structo]

I was logging in to check my email at vintage amp forum (don't get butt hurt this forum is the best!) I ran across this article

http://vintageamps.com/what-does-%e2%80 ... /#more-458

Nice, the Amplitrex.

I wonder why there aren't more devices like that being marketed.

A bit of sticker shock at $2,675 but I suppose if you owned a tube store it would just be tools of the trade.

I wonder why you couldn't just build a power supply then have some sort of PC interface to graphically show the attributes such as Gm or other properties?
I suppose it boils down to the software development.

Me want.

[selloutrr]

you can come play with mine Structo we should build something!

[Structo]

SWEET! You have both!

How does the Maxi differ from the Amplitrex?

[selloutrr]

The maximatcher is for octal socket output tubes only. I sprung for the socket savers, and 7027, and el84 adaptor sockets.
It offers up to 500v in detent presets with fixed bias points.
using a scale as long as the tubes fall between in the recommended settings they are good. Then you switch threw the sockets to see how closely the tubes are matched.

I find it to be quick and accurate for basic matching then if I have a tube or tubes in question i'll test them more in depth on the amplitrex. The main reason I picked up the Amplitrex was so I could test preamp tubes, and rectifiers. I had amplitrex write a custom program and build a test box for testing 6K11 12 pin preamp tubes since I see a lot of Ampeg V4 / VT22 / VT40's on my bench.

I think the next step is to setup a dedicated O'scope, power amp and speaker with a switchable headphone jack for testing microphonics without having to run test cables across the bench.

[Structo]

Nice setup.

I take it you are a full time amp tech/ repairman?

[selloutrr]

It's more of a full time hobby of amp collecting.

The Techroom allows me to buy broken and vintage gear and bring it back to life. I rent the amps in the studio to cover the cost of NOS tubes.

my day job is audio engineering. well it was, we were let go a month ago, but after 7yrs of solid work with less then 3 months off total in that entire time it's really relaxing to not have the stress. I've lost 10lbs from not having to eat restraunt food twice a day and my feet and back finally stopped hurting.

Maybe I will turn the hobby into a store front business? I already fix most of the local musician's and pro's amps i just hate the idea of owning a business in california

[Deric]

Does the "short" test socket on the Maxi Matcher test for shorts with voltage and/or load on the tube?