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In Reply to: RE: Audible Illusion Modulus preamplifiers- 6DJ8 family ratings and AI tube recomendations posted by Michael Samra on August 15, 2010 at 14:45:54:
Micheal Samra,
6DJ8 origins: Interesting about the 6DJ8 being originally designed for instrumentation and other non-audio uses. Among the uses I've read is in high-frequency circuitry of Radar- and this is where the Russian 6H23pi went.
Microphonics: In 1991, thinking I should begin thinking about retubing the SP10 after 4 years, I bought some 6DJ8's from a California electronic supply and these turned out to be unmarked Sovtek 6H23pi-EB's from - this is before Ebay.
Since the tubes in the SP10 then were the factory originals and had tube rings on them, I had never experienced microphonics. And, it was a shock- there were a couple of these Russian tubes tubes that were so microphonic, I could hear it if only rubbed the gain knob with my finger. If I tapped the gain knob, it rang and echoed!, if I changed the gain -it's a stepped pot, each indent sounded like someone hitting an anvil with an elegant brass hammer. Best of all, if I leaned in and shouted near the tube, it would actually amplify the sound and was understandable at the speakers. Imagine how stupid I looked doing this- and imagine what I was saying- I used my favourite Hungarian invective.
Modifying stressful circuits: In the mid 90's, I asked ARC and a L.A. technician who I trusted completely- Bob Hovland!- about specific and general lowering of the V's and W's to the SP10 gain tubes to take some of the stress off. However, in both cases there was vehement disapproval, saying the dynamics, transient response would be compromised, therefore it would become dull, the imaging would flatten, lower gain, looser bass, and about in every way not be as good. In effect, they were attributing a lot of the sound quality to pushing the tubes. As I'm far more mechanically- minded than electronic, the result was a collection of 109 tubes,..
The AI has always been intriguing to me as impressions seem to be always positive and I like the idea of high performance from a simpler solution- the SP10 has a lot of parts including 15 tubes on two chassis.
As well, I've not heard one in along while, and not heard an intelligently modified one as it seems our friend wheezer has done. This is a talent I wish I had, but so far I can't invent improvements to Mr. Johnson's design.
6DJ8 optimism: There were times I was so frustrated with getting the SP10 tubes right** that I thought to sell the SP10 and return to my first serious preamp affair - the SP8 I bought in 1985 and which uses 12AX7's.
** The V.P. of Gold Aero came to my house and we went though 20 MC phono grade 7308's to find two that worked properly in every way, plus since 1991 I've bought 109 tubes of this family, spending many hours shopping.
But, there is hope: the SP10 sound still bowls me over after 23 years' ownership, and my recent (1.10) retubing was encouraging as all four of NOS Valvo E188CC's I selected from the 22 worked and I'm even trying V-9 and V-10, the line stage gain tubes without tube rings. Though, I think I'll need to put the rings back on- I'm convinced the lows and highs were suffering, it was a pleasant experience that it was even possible to try it.
A very pleasant surprise in the retubing is the sonic quality of the Tungsram red label E88CC- the slightest warmth/darkness but still detailed and dynamic. Here I've got 6 of these doing follower detail where EH6922's would be just as good at less cost. This is a reminder too that the current production EH6922 is really just fine- not perfect, but not terrible in any way, plus very tough.
Still, I suppose audiophilia is the thrill of the hunt. I have a friend with old cars who completely loses interest in a car if it doesn't give him any trouble or need restoration.
Cheers,
Bambi B
[ Say, I rode in an acquaintance's new Buick LaCrosse last week, and that was the most encouraging GM car I've been in since I had my 1955 Coupe deVille in the '80's. -That 331 Cadillac V-8 was the smoothest running engine I know.]
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Follow Ups
- The infuriating 6DJ8 - Bambi B 08/15/1015:49:16 08/15/10 (1)
- RE: The infuriating 6DJ8 - Michael Samra 17:16:23 08/15/10 (0)
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