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Does anyone actually know what the difference is, if any, between a FENDER GT-12AX7R and a FENDER GT-ECC83S.
I got a brand new Fender Bassbreaker 30R in the shop for repair and it has installed GT-ECC83S at position V1 and V2 (input gain, tone buffer and effects drive) and GT-12AX7R at t V3 (phase splitter).
Asked Fender directly and could not get an answer there either?
Anyone out there got any insights?
Thanks
What does the schematic specify?
From what I can determine 12AX7 and ECC83 tubes are interchangeable, with one being the American name and ECC being the European designation. There is a lot of misinformation out there regarding the "s" at the end of ECC83S. I have seen people say it refers to it being made in Slovakia, that the S stands for short plate, or even spiral filament. I don't know what the S stands for, if anything.
The only word of caution is if you use ECC803 tubes in a combo amp, it may be subject to microphonics, as it is a long-plate version of the ECC83. My 1977 Deluxe Reverb (bought used), came with 4 ECC803 tubes in the 12AX7 positions. I bought 4 new EC83 tubes and swapped them out (before tube prices went crazy). Probably wouldn't have needed to do this, as I don't play extremely loud and I didn't notice any microphonics, but now I at least have some additional spare preamp tubes.
+1Quote:
Originally Posted by Michael Smith
I eschew long-plate subminiature tubes for that very reason, especially for the gain stages and phase inverter.
I did run across this article about the different Sovtek 12AX7 variants. They also make a 12AX7LP (long plate) which I didn't include in the attached.
https://i.imgur.com/l2c0Ru1.jpg
It would've been nice if that data sheet also included the S/N ratios for each variant.
I couldn't find any schematics for that amp, but the Fender literature says it has 3 12AX7 preamp tubes. On older Fender amps, I have only seen 12AT7's used as a phase inverter, so perhaps they are using something other than a tube for the phase inverter? It would be nice to see a schematic for this amp.
Edit: I found the user manual for the amp. You may not be able to read it clearly, but for Tubes it says V1-V3 7025/12AX7/ECC83.
https://i.imgur.com/bGGm3LC.jpg
We are talking Fender Bassbreaker 30R in this case. Brand new unit and it has GT-ECC83S in V1 and V2 and GT-12AX7R in V3. Fender schematics for exact same unit (obtained from Fender ) specifies "12AX7A" in all positions - parts list from same Service Manual specifies "TUBE GT-ECC83-S SELECT" for all positions.Quote:
Originally Posted by phantomman
So - still no wiser ....
Technically the 12AX7A is a low-noise equivalent to the now long-discontinued 7025.