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What is different? 7868s or 7591 outputs I assume. Otherwise is the preamp the same?
Steve
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I had a IV and 2 version 1s.The IV had 7868s and 6eu7s, all through the preamp section and as driver tubes.
One version 1, had 7591s and 12ax7s all through the preamp and as driver tubes. It is an early version.
The other had 7968s and 6eu7 as drivers and 12ax7s in the preamp. It also had a multiplex out rca jack for a stereo signal light on an external Sherwood unit. Just the light.
So go figure.
A question for everyone. The heater filaments on the phono section 6eu7s in the version IV I were a/c.
The heater filaments on the phono preamp tubes in version 1 were d/c.
Would there be any explanation for this. I have the schematics for both, that I can post.
Other than that it looks like they boosted the power ratings on these receivers, from version 1 to IV. Version 1 is 32 watts/channel, advertised as 64 watts, and Version IV is 40 wpc., advertised as 80 watts. I think they just upped the voltages that the output tubes were run at. Version 1 plate voltage 412v, screen voltage 402v version iv plate voltage 438v, screen voltage 426v.
Thx
David
Edits: 04/14/14 04/14/14
They changed from 12AX7s to 6EU7s in the -IV - equivalent with a different pin-out. Email for a schematic: tbavis(at)rochester(dot)rr(dot)com
Mostly subtle changes and most of the IIIs I have done have 7868s as well.
I personally like the 7868 better than the 7591 even tho they are electrically equivalent..I think the way the pins connect directly inside the bottle and seal,give the 7868 a slight sonic advantage.That's my experience..YMMV.
Honest amplification is better than excessive 2nd order distortion anytime.
My understanding is the S8000 and S7700 used the S5500II preamp in all versions so probably the same or only minor differences.
Don Brian Levy, J.D.
Toronto ON Canada
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