# preamp tube question



## Waterloo (Dec 25, 2012)

I have an '83 Princeton reverb II, bought it a year ago. Although the tube chart on the inside of the cab recommends an AT7 in v2, this had an AX7 in that spot. The original owner passed away so can't ask him about the amp history (any mods done, etc).

Although it sounded fine, I changed the preamp tubes a couple of weeks ago, as they were all microphonic but put an AT7 (instead of the AX7) in v2. On Friday, I noticed the amp just didn't sound right, nothing terrible but just off. Yesterday while at a jam, it really went downhill, total distortion, and sure enough the new AT7 in v2 was microphonic. 

Here's my question: is this just a one-off defective tube or is something else going on elsewhere in the amp that would cause the AT7 to fail so quickly (in only 2 weeks)? 

I'll probably take it into a tech to have a look-see but welcome any thoughts on this.


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## dtsaudio (Apr 15, 2009)

According to the schematic, V2 is the reverb driver. 12AT7's are a much more robust tube than a 12AX7 and should be in that location. It is possible you got a bad tube.


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## Waterloo (Dec 25, 2012)

That was my first thought so I'll follow it along (I put in another at7) and we'll see if how it goes.


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## mhammer (Nov 30, 2007)

Q: Would the long-term use of an AX7, at a point in the circuit where an AT7 is called for, have any impact on any associated electro caps?


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## dtsaudio (Apr 15, 2009)

Not likely. It's more likely the 12AX7 would have a short life.


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