Quote:
Originally Posted by big dooley
V1 and V2 are the gain stages
V3 tone stack / cathode follower
V4 PI
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That is correct and this applies only to modern Marshalls using four ECC83/12AX7's in the circuit.
Please note that the preamp tube is actually two identical circuits inside of one glass envelope. However, in the real world, they might not be that identical. When replacing tubes, it is nice to have a tube tester, because it will tell you how close each half is matched. It is imperative to use a close matched 12AX7 on V4, the phase inverter. On V1 I put a tube that exhibits high gain and V2 gets a similar treatment (You may not want as much gain, so you could use a tube that measures on the low side. I have used 12AX7's that only read 60 per cent in V1 and V2 and the owners are thrilled with the sound they get.) V3 isn't as critical, but I still put a good tube in it anyway.
I like the sound of almost any NOS tube. It's a joy to be running tubes in your amp with 1955 date codes. Telefunkens, RCA Gray and Black Plates, Sylvania's, GE's and Raytheon's are all good tubes (as long as they test in an acceptable range).
I have all GE 12Ax7's (1964 date codes) in my DSL401 with Canadian made RCA Black Plate EL84's. What a monster! Total difference in tonal qualities versus the stock OE tubes.
I wish I could bring some of my tubes and my tester up to where you live and we could have some fun dialing in your TSL122. However, you know if you have a question you can contact me here or by PM.
Marty