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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: Tube rolling for EAR834 Phono Preamp? posted by Marc Bratton on February 19, 2000 at 09:12:22:
Hi all,Well, based on analysing the Circuit, the Middle Valve (V2) should allways be a 12AX7/ECC83 Type. This Valve is within a NFB Loop and determines the accuracy of the RIAA EQ. Using a Lower Gain (Mu) Valve like the 5751 there will very literally "turn down the Bass", not much but notable.
I suspect teh Box Anode Mullard military version (forgot the number) followed by the Brimar CV4004 are the best choices here.
The other Valves are a lot less critical with respect to the EQ accuracy but will also substantially impact on the sound.
In the Input position I personally (as someone already remarked) suggest to try a 6072A or 12AY7, obviously the 5751 can also be used, as can the WE420 and others having a fairly high Mu, low Gm and the standard 12A..7 pinning and 12.6V 0.15A Heaters.
The final Valve is a Cathode Follower. There again many types are possible. I allways find the 12AX7 to sound extremely "foggy" in such an application, both the 12AT7 (ECC81) and 12AY7/6072A are known to work well in such applications. Others really low-mu types like the 12AU7/ECC82.
I suspect that with all these different options in the various position it should be possible to "tune" the sound very substantially "to taste".
The 6072A sounds very delicate and open, the 12AU7 in the Follower Position quite dark, this may be a very nice combo if one of the brighter Cartridges is use or the system is too bright. The 12AT7 as Follower can sound overly bright, as can the 6072A, so perhaps that is best for brightning up a slightly dark sound.
Later Thorsten
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Follow Ups
- Re: Tube rolling for EAR834 Phono Preamp? - Thorsten 10:15:23 02/20/00 (0)
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