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I spoke with Dennis today of Cary and basically the Six Pacs "are" voiced for the Ruby EL34. This is of course not to say that the amps don't work with any tube that will handle the B+ voltage of 400 to 410 volts. The B+ choke is rated for 380mA and is really best around the factory specs of 220mA total. Dennis also stated that the "sound" of the KT90 while different if biased this low in ultra linear, would be fine biased at the 220mA.I have tried the amps with the SED EL34, which when biased at around 250mA sound very good but not as good as the Ruby EL34B and I have tried the 6CA7EH fat bottle, biased around 250 to 260mA and again the Ruby tubes sound sweeter with a better midrange. The KT90's run at the 220mA would most likely last a life time. One other note, I understand that the KT66 sounds very fine also.
ja in cloudy, windy and cool, Tucson, AZ
Follow Ups:
I have a UL amp that I just refit with tin foil caps and KT90s at 380V 80ma each for which I hope is an easy class A operation. The amp is still on the bench awaiting the time to swap out the existing GM70 amp.IS there a distinct sonic difference with KT90s at low op points?
nt
John,Thanks for the posts on the Sixpacs. I kicked off the new year with a pair of Sixpacs and a AE-3 DJH and absolutely love them all.
I upgraded the capacitors to Jensen at the time of purchase, and have been completely satisfied with the stock tubes (although your discussion with Dennis has put tube rolling even furhter back in my mind).
The only reservations I have about the AES hardware is purely superficial: I don't care for the myriad of fonts and font sizes on the faceplates, the blue LED on the AE-3 DJH should be replaced with a red LED as on the Sixpacs, the speaker binding posts need to be upgraded, and since the bias pot is hyper-sensitive, a large knob should be included. I’ve been e-mailing the techies at AES, and all of my concerns can be easily remedied with a little dedicated project time.
pot to Kirk. I do not have the adjustment know on the pot because I find that it is too easy to move the pot and throw the bias off once set.The binding posts, I replaced today with Cardas. The posts are slightly magnetic and the nut on the inside as well as the washers are very magnetic. The posts really should be of better quality. I bypassed the Jensen caps I have in the unit with some .056 teflons. Better highs and more transparency is the result.
Even the CCS circuit was designed for the 12BZ7. I tried some nice 14mm 12AX7 Mullards today and they sounded very good. The shimmer of cymbols was more brassy but overal the 12BZ7 gave a better "you are there" qaulity. The 12AX7 by JJ is also a nice sounding tube in this unit. I have a pair on hand, I don't remember why I bought them, and although not as transparent as the 12BZ7 it is a nice tube to listen to music with.
ja in cool and cloudy, Tucson, AZ
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