MC30 output tube question

[Thocom]

I have a few different single 6L6GC tubes laying around, and was wondering if I should just look for a match to one of my single tubes? Is it correct that in this circuit, matching the tubes isn't imperative?
If it's not imperative, I think I'd at least want to match the make and revision..
I have this tube, I think it's an RCA blackplate? It's got one circular getter on one side. Is that a desirable
tube?




I also have this GE (I think) with Two getters that are at 90 degrees from one another.







Then I have this RCA gray plate, with two getters at 160 degrees from one another



Any thoughts?

 

[x3workshop]

Match the brand & version with an equally good testing tube. It doesn't need to be very closely matched in Gm and current. The amp will work with mismatched brand/version, but not at it's best. My .02¢

 

[SilverTpt999]

McIntosh has always maintained that tube brand is entirely irrelevant in the unity-coupled circuit. Any four tubes (2x per mono amp) which test strong will meet spec, and should do so interchangeably.

So more than anything else, I'd say - do you have the ability to test these tubes?

 

[Thocom]

McIntosh has always maintained that tube brand is entirely irrelevant in the unity-coupled circuit. Any four tubes (2x per mono amp) which test strong will meet spec, and should do so interchangeably.

So more than anything else, I'd say - do you have the ability to test these tubes?

Yes, I do. I was thinking of picking the two that are closest and going with it.
I also have matched KT66s, but the other MC30 has GE 6L6gcs in it..

 

[4-2-7]

If it's not imperative, I think I'd at least want to match the make and revision..

That's the big thing on your power tubes.

 

[x3workshop]

Yes, I do. I was thinking of picking the two that are closest and going with it.
I also have matched KT66s, but the other MC30 has GE 6L6gcs in it..

Tom. Don't mix and match. If you need a (brand/version) match I can help you out. I'm not big on dropping KT66's in these.

 

[Thocom]

Tom. Don't mix and match. If you need a (brand/version) match I can help you out. I'm not big on dropping KT66's in these.

Thanks Antoine, I won't. I will keep an eye out for a single that matches on of the ones I have above. In the meantime, I will just use the MC240 alone and not bi-amped with the MC30s.

 

[Seamaster]

Current production Tung Sol 6L6GC work beautifully in MC30, they cost less than $200 for a matched quad. I also have a set of RCA black plate too

 

[Thocom]

Yeah, I have these that test strong, but have no match, its like a wasted tube if I don't find a second tube to match them. Its like they are wasted

 

[CruzBay]

Experimenting, I had an MC-240 I'd gotten and was testing and changing tubes.

When it came to the power tubes, I put in the 4 best 6l6GC's (mixed brands) thinking it'd work better.

It didn't sound all that good.

Changed out the tubes to matched brand tubes that didn't test as well and the sound got a LOT better.

 

[62caddy]

"The excellent performance that is inherent in all Mclntosh amplifiers does not depend on the critical adjustment of bias or balance controls in the output circuit. The patented Mclntosh circuit delivers its advertised specifications without any need for these controls and is not dependent on carefully balanced tubes for its performance."

- McIntosh Owner's manual.

However, the MA230 and MAC1500 do not have Unity Coupled circuit and do have bias adjustments. For these units, tube matching is critical to meet spec.