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I own the Audible Illusions L2 pre amp. I need a new matched pair of tubes for this pre amp. The seller lists 4 options: Balanced Triodes, High gain, Low noise and microphonics and Matching.
I believe I should choose low noise and Matching. Is balanced triodes and high gain important for pre amp tubes?
Thanks.
Follow Ups:
Your preamp uses two 6922 tubes, I see. If you're looking for sonic consistency and good (proper) operating, then you should look for tubes with all 4 criteria met. How they're wired into the circuit is important.
Is it like this? (One tube for each channel)
Chan R - Tube1-Triode1 - Tube1-Triode2
Chan L - Tube2-Triode1 - Tube2-Triode2
Or like this? (Triodes from both tubes are used for each channel)
Chan R - Tube1-Triode1 - Tube2-Triode1
Chan L - Tube1-Triode2 - Tube2-Triode2
If each channel shares a half of each tube, balanced sections and subsequently matched pairs would be pretty key and ideal. The high-gain selection may be important; below-standard gain can result in a funny-sounding amp. And fact is, most new-production tubes are not consistent whatsoever. Variation in transconductance and gain can leave you with a tube that sounds entirely different than it's spec-adhering cousin. For example, JJ 12AX7's have a reputation of being below-spec, to the point where it almost sounds like a 12AU7-AX7 mix-up tube has been placed in the slot.
And doing a little reading on the Audible Illusions L2, apparently some say the unit operates reliably ONLY with the Russian 6922's (apparently a question of plate voltage). Anything else burns up quickly, according to this review I found:
"[...] But the unit has one fatal flaw – a design flaw. While the Audible Illusions web site claims that 6922 and 6DJ8 specification tubes, other than the stock Sovtek tubes, can be used in this unit, fact is, they can’t. The unit was designed to operate at higher plate voltage attributes specific to the Sovtek tubes rather than then operating parameters of the specification. My particular unit has destroyed, in a couple of days, every NOS 6922 and 6DJ6 that I have tried other than the Sovtek tubes.
So if tube rolling is something you think you might want to experiment with, this is not the unit for you. If you stick with the stock Sovtek tubes – and they are quite nice sounding – the tubes will last about two years. I put a pair of Amperex Bugle Boy 6DJ8 in this unit and they completely changed the sound of the unit. It was breath taking, but alas the tubes were fried after two days."
Eeep
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May your tubes be lively and long-lasting. Holy be thy heater.
Thank you for the excellent reply.
you do not have to choose, those are the qualities that are matched by the seller.
AB.
small tubes are normally not used in push-pull applications. right? so critical matching makes not sense really. also right?
i assume you would not even notice if the emission of a left channel triode system differs 20 or 30% from the right one. just MY experiences...Nunki
The times, they are changing...
Edits: 04/14/14
PP amps do use small tubes in the input sections, but close matching is probably more critical in preamps and phono stages.
AB.
If a dual triode is used as a long-tailed pair phase splitter, matching is reasonably important, more for transconductance than noise or emission. Reason: A transconductance match will drive the output tubes differently (unless your amp has an AC balance control, in which case transconductance matching is not important). Emission matching isn't terribly important because the tube will be happy with any reasonable quiescent operating point. Noise isn't terribly important because at the phase splitter/driver you're dealing with the largest voltage signals before the output tubes, so the signal spends most of its time way above the tubes' noise floor.
Note that this discussion only applies to long-tailed pair splitter drivers.
Most that I've seen are single-ended, Class "A."
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