6SJ7 vs. 6SN7

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6SJ7 vs. 6SN7

Postby die Bullen on Mon Nov 28, 2011 12:48 am

One of my amps, a '58 Ampeg New Yorker, curiously has 6SJ7 in the tube chart for ch 2's preamp scribbled out and 6SN7 written in. The only other guy I know with this amp has the exact same thing on his amp. Do you think something like was a typo or is it possible the amp was intended to have the 2nd channel voiced differently? I don't have any 6SJ7's so I can't make this swap to find out what happens.

Any ideas?
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Re: 6SJ7 vs. 6SN7

Postby 6 10 on Wed Feb 08, 2012 1:26 pm

It wouldn't work anyway, as the 6SJ7 is a pentode and the 6SN7 is a double-triode. Different wiring.
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Re: 6SJ7 vs. 6SN7

Postby Teisco88 on Fri Feb 01, 2013 4:20 pm

NOT pin compatible. In the mid-1950s, amp companies (Fender did this) switched from using the 6SJ7 pentode as a preamp tube to using twin triode tubes. The 6SN7 was popular because of its association with Williamson-style amp designs. (The Williamson would have been popular with designers who were slapping together either bass amps or jazz amps--both becoming popular in the mid-1950s.) The twin triode was considered a more modern approach to preamp circuit design.

Anyone who has played a Fender 5C1 Champ and a Fender 5E1 Champ can tell you the difference. This is typical of what people have to day about the switch over: "in newer versions of this amp, the 6SJ7 was replaced by the now-ubiquitous 12AX7. Those are higher-fi tubes, in a way, that can get a cleaner signal to your power tube (aka less noise, depending on how they're used)...but at the cost of that 6SJ7 pentode mojo." The earlier circuit, with the 6SJ7 pentode, was less clean sounding.

AMPEG was probably trying to "clean up its act" like Fender in going to a hi-fi tube like the 6SN7. I don't know what kind of music you play, but there you have it.
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