[Monster Factory]

Great suggestions so far. Keep'em coming.

>What brand of tubes come in the Monster amp?

Each model is dfferent, but I tend to use JJ's more than any other brand. I sometimes use the Electro-Harmonix 12AX7EH for phase inverter positions. Sino (Chinese) have some pretty good miniatures and power tubes. Many of the newer tooled Russian tubes have reliable standards as well.

The Swamp Thang seems to be the amp you guys are most interested in and it has four JJ ECC83's, one Sovtek 12AT7 (effects loop), and the four JJ 6L6GC's you mentioned. Every amp I build is designed for the specific tube type that comes in it. 12AT7, 12AU7, 12DW7, etc., are all different in terms of gain, which affects the tube's transconductance, output voltage, operating point, etc. The ECC83/12AX7 is the highest gain on the market with a factor of 100. Real tubes aren't perfect devices and perform less than that, but you get the idea. This means that a perfect tube in the ideal circuit can make it's output voltage 100 times bigger than it's input voltage, or a 3 volt signal would become a 300 volt signal.

By way of comparison:

12AX7 = Gain Factor: 100
12AT7 = Gain Factor: 60
12AY7 = Gain Factor: 45
12AV7 = Gain Factor: 41
12AU7 = Gain Factor: 19

When you swap tube types in a fixed circuit, the new tube type won't 'perform' optimally. That's not to say, however, that it won't 'sound' exactly like you want. After all, most of the mojo of a tube amp comes from it's imperfections. Everything we like about them is something it does that it shouldn't, so mix n' match til your heart's content.