I'm going to Re-Tubes my Mesa Mark III ... however..

[PRS_THAILAND]

I am going to re-tubes my Mesa Mark III, however, I found 1 difference tube which are: SPAX7-A ... I am buying Ruby Tubes for 6L6 GC and other 4 - 12AX7 ... what can i use to replace SPAX7? Thanks.

 

[Russ]

SPAX7 = Ruggedized low noise 12ax7 type tube basically what you might get with a 12ax7wa or wb. The following a designation really doesn't mean much. The tube really is nothing special other than it is supposed to be more stable than the standard Mesa 12ax7. The tube you choose to replace it with doesn't necessarily have to be high gain because high gain usually brings more noise. Personally I don't care for the SPAX7. If you want high gain I would go with either a GT SAG high gain tube or a JJ ECC83S high gain. In the case of GT you will have choices among their 3-4 different manufacturer types that they currently use and this will allow you to vary your flavor some. I have some SPAX7s that I had bought but they are not even a matched tube. They are random in life expectancy and not really worth buying. I have one that is brand new that barely tests as new. You can specify your GT as matched also.

That or just buy yourself a nice NOS 12ax7 or 12ax7a or ecc83. Most of the NOS offerings had better manufacturing and life expectancies than current production. The older NOS tubes typically also have better gain with less noise too.