OK, so here's my learning curve about the JTM45:
There are six tubes in a Marshall JTM45.
Two of them are power tubes: KT66's. To get a matched New Old Stock (NOS) pair you're going to be laying out upwards of seven hundred bucks. So my big questions be:
- Can I use lower wattage (read: "cheaper") tubes and get a nice cranked sound out of them at a lower volume? (As far as I know, no.)
- Or, can the amp be run with only one power tube? (As far as I know, no.)
- Or, will EL34's (which are more in the range of $300 for a matched pair) work and still make the amp sound groovy (although not exactly like a JTM45)? (As far as I know, yes.)
There are three 12AX7's.
And a single rectifier tube, a GZ34.
Here's an interesting (so I thought) comment regarding the quality of different tubes from the MetroAmp board:
The consensus I am hearing is that VA KT66's are very good in relation to the tone quality compared to the holy grail GEC/Genelex/Gold Lion KT66's. This is good news and in fact the difference I hear between the GEC's and the VA's is that the GEC's have more push in the upper mids, where the VA's are a little thinner - notes on the B string are as fat as those on the G and D strings. Think of it as going from say a set of 9's to a set of 12's for string gauge, and you start to understand my interpretation.
Here's a page of information on mods for the Marshall JTM reissue.
What does all this mean? It means that somebody has to buy me a GMP45 Head.