GT Output Tube Matching Process....How Was it Done?

[DaveMcLain]

I've read a lot of stuff over the years either praising or criticizing Groove Tubes output tubes. While I've never been a big believer in matched tubes for guitar amplifiers but having some that are reasonably closely matched statically makes setting the bias easier.

What I'm wondering is what was the Groove Tubes process? From my understanding the idea was that the tubes were matched according to how and when they went into distortion. They were then grouped together with tubes that distorted in a similar way and then grouped together with tubes that also had a fairly close static match for biasing purposes. Was any of this true? Or was it all "snake oil"?

I've heard people say that their "match" was not as good as tubes from other vendors. This would be true for sure if the static match was being checked yet they were actually matched in some other way....

[Kevin]

I have no inside information as to Groove Tubes' matching process, but my experience tells me that their power tubes are simply rated according to emissions, i.e. plate current draw, at a given bias point. It just happens to be the case that tubes which draw less current at a given bias setting break up earlier, and vice versa.

No, their match is not that great, because their tubes are simply given a rating from one to ten, rather than an actual plate current number. A number six might incorporate anything from 32 to 38mA at 400V/-36V. I'm making up these numbers, because I don't actually know their test and classification parameters, but that's the idea, as far as I know. Then throw in the fact that it's pretty unlikely that they're testing them at Marshall (or whatever you use) voltages, and you're allowing for a pretty sloppy match.

Unless you want a product which is sold exclusively by them - their xf2 copies, for instance - it's better to buy the equivalent tubes from somebody who matches a little better. If they have any knowledge regarding their products, they should be able to set you up with early- or late-breakup tubes.

[robert]

Hi,

I prefer the TAD matching method:

A 24- hours burn- in, and then selected for Plate Current and TransConductance.

Regards

Robert