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RE: Sherwood S-5000 preamp section - 3 tubes in the lines stage - what are they for and...

12.10.199.12

Eli Duttman

In Reply to: RE: Sherwood S-5000 preamp section - 3 tubes in the lines stage - what are they for and... posted by airtime on May 26, 2015 at 08:40:01

Look at the schematic! V3 is set up as cathode followers that drive the recording O/Ps, as well as the rest of the amp. V4 & V5 are voltage gain blocks that compensate for the losses in the signal shaping circuitry.

For reasons of gm, the 12AU7 makes a better cathode follower than the 12AX7. This "smells" like a rare case of "bean counting" on Sherwood's part. Not inventorying 12AU7s saved money.

First, listen to what Jim McShane says, as he's very rarely wrong. If, on the outside chance, you are still plagued by hum, try Sovtek 12AX7LPS tubes. The 'LPS is a genuine 7025 equivalent that contains a spiral wound, hum bucking, heater. ;>)

Eli D.

Follow Ups:

RE: Sherwood S-5000 preamp section - 3 tubes in the lines stage - what are they for and... - airtime 13:06:18 05/26/15 (1)
Jim recommended the Genalex B759 or the LPS for position V5. Before I finalize the order I'll ask him about the 12AU7 option.

My OP was to see if any one particular tube would be better in a particular position. However as stated the V5 position does have that one "hum" restriction. The Genalex or the RCA tubes are not second rate tubes.

The TungSol's sound wonderful in positions V3&V4. They replaced the original RCA's and the sound seems to be cleaner or tighter. I'm assuming there was some "the new toy always sounds better" reviewing. but they are good tubes.

charles
- RE: Sherwood S-5000 preamp section - 3 tubes in the lines stage - what are they for and... - Eli Duttman 17:28:34 05/26/15 (0)
  "Before I finalize the order I'll ask him about the 12AU7 option."
  
  Installing a 12AU7 as V3 is NOT plug & play. Parts value changes are needed. Leave well enough alone. I was "belly aching" about corporate cheap skates. Sherwood deserves credit for buffering the recording O/Ps. I just wish they would have gone "whole hog".
  
  Eli D.

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