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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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In Reply to: Is it safe to substitute 12ax7's with 5751's... posted by DanS on June 12, 2006 at 15:48:04:
Yes I have found it safe to sub the 5751 but according to some it may alter the electronics of circuit in a fundamentally important way. I don't think that is prices have skyrocketed although showing signs of cooling off or that Joe of the Tube Lore fame felt it was a reasonable alternative. It may not accomplish what you want in your system but it appears safe enough. YMMV.
I still find the Sylvanias Triple Mica Black plates 1950s to be the quietist and most well defined. I find as a general rule that the grey plates of all the brands offering both black and grey, that they grey plates are a bit flabbier in the bass and provide less definition all round but are richer sounding. I can't comment on the Sovtek but the ubiquitious NOS 70s JAN which can still be bought for $15 is low gain but doesn't posess the quiet and well defined nature of the triple micas. I agree that the GE are abundant 50s "NOS" 3 mica but aren't very cheap. Also beware the NOS 5751s are frequently low testing even weak or poor. A strong pair seems the exception rather than the rule. I have too many GE 3 micas black and grey but I have to test them and figure what they should command. I didn't pay the good old day prices sub $10 a tube. If you are interested LTMK.
Back to the orignal question I left the 5751s in the 2nd position in the line stage except for a Brimar 12AU7 in 3rd and put a 12AX7 back in the 2nd position of the phono stage the Brimar in 3rd again. I would assume that this would allow more current to run and booster the power to the remaining tubes through presenting a low impedance to the beginning of the chain.
I also found I simply had too much gain. Alas the modding took the adjustable gain out of the circuit. It was hard wired to high for MC cartriges.
My SP6B came with its original Bel "India" 12AX7s (a Phillips Subsidiary which also owned Mullard) which are quite functional today some 29 years after the original owner claims they were installed. I also found that a single 60s BB Mullard 12AX7 did not do the trick.
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Follow Ups
- Re: Is it safe to substitute 12ax7's with 5751's... - Mechans 01:58:01 06/14/06 (0)
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