2. tech-talk
  3. 1228183582

Installed Wrong Tube 12AX& instead of 12 AT7

I just got a MC275 yesterday and the seller mistakenly installed a 12AX7 into the V4 socket (originally for 12AT7) It didn't sound clipped or it didn't stop functioning except that one channel was louder than the other, but I really don't know if the mistake has damaged the amp, or the damage is slightly and I don't see or hear... I am curious to know if anyone has done the same and what happened... Also, what's most likely is to be damaged if this mistake occurs. What should I look out for... or how do I check. All your inputs will be greatly appreciated.
infinity_audio

Showing 3 responses by ghostrider45

ghostrider45
449 posts
 
12AX7 has more gain than the 12AT7, but is electrically compatible (pinout and voltage/current requirements). No harm done.
ghostrider45
449 posts
 
The only defect in a tube that can cause damage is an inter element short. These are common enough in power tubes where they usually take out a resistor and/or blow a fuse, but are rarely seen in small signal (dual) triodes like the 12AX7 or 12AT7.

You should be fine.
ghostrider45
449 posts
 
No matching required. Power tubes need to be matched (unless the amp supports individual bias adjustments per tube) to ensure that the tubes equally share the load. Otherwise one tube might hog most of the load, limit ultimate amp performance, and fail prematurely.

Small signal tubes are self biased, produce voltage gain only rather than power, aren't running parallel and/or push-pull, and don't need matching in normal amplifier topologies (including MC275).

Feel free to experiment with different tube brands. Tube rolling is part of the fun.
More to discover