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... should I use any particular tube in a particular position in the line stage.Tubes, V3,V4 and V5 - what function do they have in what positions?
Is there any particular tube order to use the right tube for the right job?
I have RCA black plates, New issued TungSol's and have a Genalex (on order).
The only caveat is if I put the tungSol in V5 it hums. If I use the RCA's there is no hum. So Jim recommended I try the Genalex in the V5 position being hum is a problem.
Edits: 05/26/15 05/26/15Follow Ups:
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.
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
"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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