How To Match Power Tubes

Hello posters,
I recently blew a 6550 tube and the associated resister in my ARC amp. I purchased 2 pair of matched EH 6550's from a company which is highly regarded here on Audiogon, and then turned my amp and these tubes over to a very highly regarded technician to replace the resister and install the tubes. The technician tested the tubes before installation and called me to say that they were very poorly matched. He said he could get them to bias, but they wer so far off from proper matching, that they would never sound good. He then spoke with the tube supplier on my behalf, who sent him two additional matched pairs which were properly matched. Had I not taken the amp to the technician I would have never known that the tubes were not matched, and I would have thought that EH tubes were not as good as the Swetlanas that were in the amp previously.

Given this experience, I no longer trust that tube sellers are going to carefully match tubes, and I would like to purchase a tube testor which is capable of makeing the measurements necessary to determine if tubes are properly matched. I would definitley like to be able to measure and match 6550's and KT88's. Can anyone reccomend a particular brand and model of tube testor which will handle these tube types? The second question is, which measurements must be made to properly match power tubes. Third, do signal tubes such as 6922's need to be matched in preamps, and if so, is there any brand and model of tube testor that can handle most of the tube types that we are likely to encounter in todays amps and preamps. From what I have read, it appears that Hiccock was the ultimate tube testor in its day, but I have seen many different Hiccock models offered for sale over the years and I do not know which models handle which tube types.

Let me thank you in advance for your assistance and for reading this very long winded question.

it seems that your tube amp does not have bias adjust screws on the outside of the chassis? The type can be adjusted clock-wise/anti-clockwise using a screw-driver. Is this a correct assumption on my part?
If you do have such bias adjust screws, you don't really need matched tubes.

If you don't have these bias adjust screws, I've heard from people who have vastly more tube experience than me that you STILL do NOT need to have matched tubes! Tubes mismatched as much as 20% work just fine & the sound is not compromised.

So, is it possible that the technician simply scared you for no reason at all?
Someone correct me if I'm wrong. Thanks!

I got into this a while ago when I owned an ARC VT130se. This particular amp required 4 matched 6550's since the bias adjust controlled all 4 of them. There were 8 total.

After contacting a couple of tube persons and waisting time and money on testers, (AVO 160, Hickok 539b & TV DU/7) I came to the conclusion that you're better off finding a trusted source to do this for you with power tubes. I had good luck with Jim Mcshane and Andy Bowman at Vintage Tube. I would have to agree that the maxi matcher would be your best bet if you were going to try this yourself. Note that I still use my testers for testing tube condition and signal tube comparisons.

As I understand it, an accurate way to see if the tubes are matched is to test their plate current while they are idling on your amp. Tube testors don't have the equivelant power that your ARC amp probably has. I have been told this by a number of authorities on this.

You would have to collect a number of tubes to find a matched set.

I've been told that the plate current at the Amp's equivelant current level is what you match to.

Regarding matching, note that ARC uses a push pull method for its power tube - that's why they should be matched.

The tester that I like is the TV7 D/U. There's a lot of them out there and there's a well respected person, Dan Nelson that calibrates them.

If you need further sharing of my experiences with this, drop me an email. I don't consider myself an authority on tubes but I have played around this stuff quite a bit.

Buy a venerable, cosmetically challenged but properly calibrated Hickok tester; you will have the satisfaction of checking the tubes periodically. A decent working Hickok tester is better than money in the bank.
For matching power tubes, short of a curve tracer, a Maximatcher would be the best and easiest to use. It measures plate current and transconductance at two different plate voltages and has several bias voltages available. At 425V plate, it provides a more "real world" test than most tube testers for 6550 type tubes.
All Hickoks and all the vintage testers test at to low a current to match tubes properly. With some tubes you can set the bias and transconduction range at a point where you can get some meaningfull measurements, some you can't. If the amp has fixed bias, use it to test tubes.