Tube rolling for Art 27a

[Pcosta]

Anyone here experiment with different 6922's than what is provided from factory.

I also have some 6550 tubes and was wondering if they can be used in the Art 27a.

[Big Dog RJ]

Personally, if I were the owner of any of CJ's latest ART series amplifiers, I would not tube roll. It defeats the purpose of this particular series.

This is CJ's top of the line, and after JF took over, these are his designs based on Class A circuits. Therefore, the tubes that JF has finalised on have been optimised based on Class A output stages. Quite different to the original ART series, which were based more on Class AB operation.

As of this date, I am not aware of any Class A circuits based on the 6550's. The majority of this tube topology were used in Class AB designs, by many other reputed makes: ARC, VTL, Manley Labs, VAC, Jadis, Sonic Frontiers. These were the ones I've owned in the past, and all the tube stereo and mono power amplifiers that I had, used the 6550 type Output tube in a Class AB config.

The KT series tubes are quite different. They can operate on a higher voltage, given the right amount of current, and when designed around a Class A circuit in the Output stages, the KT series can actually be modded to perform at much higher levels, compared to other tubes in a push-pull config.

So, starting with KT88, KT90 then KT120, KT150 and KT170, the later ones are real power envelopes, capable of high Class A bias. In fact, I've got my CJ monoblocks modded towards a higher Class A bias of 60w, from the nominal 125w/ch (Class AB) that they're rated at. That 60w of Class A is pure finesse! Superb control with difficult loads on full range Stats.

This info is something I've learned along the years from my long term trusted CJ techie. However, your question may seem simple enough, it's something beyond my pay grade & knowledge to answer. Therefore, my best advice is to ask JF himself! After all, he's the sole designer of the ART series and will certainly know.

One small question, why on earth would you want to tube roll the ART27A? Isn't it's performance good enough?

Wondering if you would actually prefer the Class AB operation based on 6550's and others like the EL34's, in which case the Classic series offers this type of sound. Definitely not the ART series. To me it may seem that you're not happy with its sound... hence the reason to tube roll...

That's quite fine because it's a highly personal preference, and you must enjoy your music with what makes you happy. I would still check with JF first. Hope it works out well.

Cheers, RJ

[Big Dog RJ]

Speaking of Class A output stages, I do remember once few years ago, home trialled the Kondo Overture integrated amplifier. It was a pure Class A design but based on EL34's and it handled my previous Quad ESL 2905's flawlessly. It was supremely fine. So I'm thinking those types of tubes could well be used in Class A circuits but perhaps they're specs are used to the Max... don't know. In which case, maybe the 6550 tubes can also handle a higher Class A...?

Mmm ... need to call and have a chat to techie tomorrow arvo.

Until then, hope you manage to get a response from JF and do let us know what his advise was. Even if he said "go fly a kite"... which we've heard from him before. Of course, more diplomatically put...

Cheers, RJ

[Joe Appierto]

RJ's recommendation to contact Jeff is spot-on as RJ stated, he's the designer.

From a sheerly point-of-information perspective, this is an AI generated response I received online:

"Yes, 6550 tubes can be used in triode amplifiers. The 6550 is a beam tetrode tube that's often used in audio service and is considered to be one of the most reliable and versatile audio tubes. While most 6550 tubes are used in push-pull configurations for maximum power output and efficiency, it's possible to build a triode amplifier using a 6550 tube."

That having been said, we get back to asking Jeff because if he specifically designed the 27a to use only KT88 tubes then substituting any other type obviously wouldn't be a good idea.

If I were a betting man, I'd say you could use 6550 just to satisfy your curiosity.