I have to disagree with the methods discribed to match tubes. You can not match tubes using a tube tester along " (AVO 160, Hickok 539b & TV DU/7) ". You do need a device to host the tube that's being tested for matching. That device could be an amp or a tube tester. You then need a way of measuring bias current. You can buy a bias probe and meter on ebay, or you can make a bias probe cable and use a multi meter or you can modify your amp to behave like a bias probe by adding resistors which alow the measurements to be made. So lets say you measure your tubes....and you make this simple....lets say you use a tube tester to host the tubes and in adition you use a bias probe. So you run 4 tubes thru the process and you find you have IP (bias current readings from probe) of 24.1, 23.9, 22.9, 23.1 and you find your tube tester says the transconductance values are GM 15000, 14900, 14000, 13900. what does this mean. well it means you have two matched sets. The pair that comprise of IP of 24.1, 23.9 with GM's of 1500, 14900 and the pair that comprise IP 22.9, 23.1 and GM's of 14000, 13900 are the two matched sets that must be used together . In the example I gave, we are testing 6550s' which have an expected transconductance value when new on my tester of 11000 which would make all tubes in this example score 126% or better.
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.
Thanks,
Dennis
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.
Thanks,
Dennis