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

Posted by Eli Duttman (A) on May 26, 2015 at 10:43:24

In Reply to: 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.

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