James Freeman
Rock Star
- Messages
- 3,191
It has been known for over a decade that Russian 12ax7 tubes (Tung-Sol, EHX, Mullard, Sovtek) from New Sensor Corp with the spiral filament fail in cathode follower stages because of their lower Cathode-to-Heater voltage resilience.
Mesa/Boogie only uses Chinese tubes there and suggests not to use Russian tubes in any CF stages like Tonestack and FX loop drivers.
I have a theory.
The Russian spiraled filament strand is almost half as thick as the Chinese non-spiraled filament and has less coating.
Cathode follower stages sometimes have 150v to 300v on the cathode and more often than not cause failure of this hair thin filament by shorting the filament to cathode due to much thinner insulation.
JJ ECC83S also have spiraled filament but it appears to be slightly thicker than the Russian spiraled filament and people report it's more durable or just as durable in CF stages as the Chinese tubes.
Mesa/Boogie only uses Chinese tubes there and suggests not to use Russian tubes in any CF stages like Tonestack and FX loop drivers.
I have a theory.
The Russian spiraled filament strand is almost half as thick as the Chinese non-spiraled filament and has less coating.
Cathode follower stages sometimes have 150v to 300v on the cathode and more often than not cause failure of this hair thin filament by shorting the filament to cathode due to much thinner insulation.
JJ ECC83S also have spiraled filament but it appears to be slightly thicker than the Russian spiraled filament and people report it's more durable or just as durable in CF stages as the Chinese tubes.
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