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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
Ag insider logo xs@2xdgclark0007
dbevolution
5 posts
 

Hello to everybody.

 

I’m from Italy, the name of my Company is dBevolution.

I would like to write something about my experience with Maximatcher and the Sales Manager Mr. Peter Toms.

I ordered and paid one Maximatcher and one Maxipreamp on 8 November 2021 (order No. 606).

Today 28 May 2022 (after more than 6 months) I didn’t receive the instruments, Italian customs told me that the attached documentation from the seller was incomplete and the parcel was sent back to the seller MORE than 3 months ago, but Mr. Peter didn’t refund me.

I sent him many email, but usually he reply to me after some days (probably it’s not his interest to resolve the problem), and he never sent me a refund and I never received the instruments.

Lately he stopped to reply to me (he don’t reply anymore).

If the situation will be not resolved, I will take a legal action.

 

So…pay attention before to buy from him

Post removed 
russ69's avatar
russ69
3,519 posts
 

When you buy a set of matched power tubes the box should have the measurements written on the box. When you get the tubes, install in your amp and write on the top of the box which position the tube is in. 1,2,3, etc. When and if a tube fails you will have the spec for the replacement tube. 

jea48
4,448 posts
 

@dgclark0007

What model ARC amp do you have? The VT series therein, VT50, VT100, VT100 MK 2 series requires the 6922 signal tubes must also be biased.

I believe, looking at the schematic diagram for the ARC CA50, the 6922 tubes also require biasing. Especially the 6922 driver tube.

The 6922 input and driver tube must be closely, tightly, matched. Especially each section of the driver tube. If each section of the input and driver tube are not tightly matched you will not be able to bias the tubes to meet the required ARC specs.

https://www.arcdb.ws/Database/CA50/ARC_CA50_schematic_and_parts_list.pdf

 

jea48
4,448 posts
 

Example:

Here is the procedure for the ARC VT50 when retubing the amp.

https://www.vintageshifi.com/repertoire-pdf/pdf/telecharge.php?pdf=Audio-Research-VT50-Bias-Adjustment-Manual.pdf

https://www.arcdb.ws/model/VT50

Trim pots for biasing the 6922 input and driver tubes are found behind the left and right channel side panel cover plates of the amp.

FWIW, nothing is mentioned in the VT50 manual about biasing the 6922 input and drivers tubes when installing new 6922 tubes.

VT50 Wiring schematic diagram.

https://www.arcdb.ws/Database/VT50/ARC_VT50_schematic_and_parts_list.pdf

 

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