12AX7 vs 7199 Tube..

[Mark]

In restoring my Sentura I head, I've discovered that the previous owner put all 12AX7 tubes in the 3 pre-amp sockets. According to the schematic, it should be a 12AX7, 12AU7, and a 7199.

It doesn't look like there was any modding done to substute the 7199 for a 12AX7, ad I hight doubt that the previous owner had that capibility, as all the baby tubes were an Radio Shack brand.

Any ideas ??  I take it I need the 7199 in there..

[Joe]

: It doesn't look like there was any modding done to substute the 7199 for a 12AX7, ad I hight doubt that the previous owner had that capibility, as all the baby tubes were an Radio Shack brand.

: Any ideas ??  I take it I need the 7199 in there..

It certainly wouldn't work at all without mods... and if it has been modded for a 12ax7, I would certainly "re-mod" it back for the 7199!!

[Ryan Phelps]

: In restoring my Sentura I head, I've discovered that the previous owner put all 12AX7 tubes in the 3 pre-amp sockets. According to the schematic, it should be a 12AX7, 12AU7, and a 7199.

: It doesn't look like there was any modding done to substute the 7199 for a 12AX7, ad I hight doubt that the previous owner had that capibility, as all the baby tubes were an Radio Shack brand.

: Any ideas ??  I take it I need the 7199 in there..

The 12AU7 has a lower amplification factor (17) than the 12AX7 (100), so you definately want the 12AU7 to avoid overloading that stage. The 7199 combines a medium-mu triode with a sharp cut-off pentode. The 12AX7 is a dual hi-mu triode.....a completely different tube! So buy the correct tubes (New Sensor in New York carries all of these.....not expensive) and put them in! Good Luck!