Just thought I'd chime in with some tube recommendations. I've tried well over 250 different tubes (types/variants/brands) in the mj2 over the last 3 plus years, and bar a few exceptions, 12AT7/ECC81 and 12AU7/ECC82 (and some equivalents) are by far the best I've heard in it.
They do require 6922 to 12AT7 adapters.
Which ones to go for will depend on preferred sound signature, but in general, they tend to have a bigger and deeper soundstage, definition, and holographics.
My prefered sound signature is relatively balanced, not too warm for the most part, leaning on a very slight V curve, though there are some with a warmer bottom end that do also sound very nice when the mood/music suits.
In relation to my preferred signature, my favorites are:
- Valvo 6201 (pinched waist double mica, and pinched waist triple mica) non pinched waist Valvo 6201 from early to mid 60s aren't as good, but still pretty decent
- GEC A2900
- Mullard 6201 (generally a lot cheaper than the above, which have got considerably more expensive over the past 2 years), warmer than the above tubes, but otherwise similar.
- Telefunken 12AU7 (smooth plates sound a little better than ribbed, but both are very good)
- Telefunken ECC801s - very neutral, can sound a bit thinner than others, especially if you're used to warm tubes, but incredible definition.
- RCA 12AU7 (side getter, clear top) - very cheap (around $25 to $30 a pair), quite warm, with a very 'tube' sounding richness in harmonics
- Telefunken 6211 (gold pin) - lighter on the bottom end, but a very mice lift around 10khz, which sound incredible with airy vocals or bowed strings
- Telefunken ECC81 - late 50s/early 60s 45 degree angled getter
- Tung-Sol 5814A - Good all rounder at a decent price
- RCA 12AT7 - black plates, D-getter
- Philips/Valvo ECC81 - Late 50s to early 60s (Heerlen factory code)
But there are several others that are also decent. My absolute favorites, and ones that rarely leave my mj2 are the triple mica Valvo 6201.
Another favorite by a lot of people from the Lyr rolling thread (many of which actually have an MJ2), is a late 50s 7316, usually Amperex or Philips branded (Heerlen factory codes). I haven't actually tried them so can't comment, but a few people who's ears I trust swear by them.
There are also other 12A*7 variants that are good, but be careful with trying them, as not all of them are within the 415ma heater current limit of the MJ2. Here's a short list of ones that do and don't work if you're keen on experimenting with cheap finds on ebay, but it's far from definitive:
Yes:
12at7 - 300ma
12au7 - 300ma
12AX7/ECC83 - 300ma
6201 - 300ma
7062/E180CC - 400ma
7025 - 300ma
7728 - 300ma
7729 - 300ma
6681 - 300ma
5751 - 350ma
6211- 300ma
6679 - 300ma
NO:
12az7 - 450ma
12ad7 - 450ma
6965 - 450ma
6414 - 450ma
6829 - 450ma
There's a good reference to the different 12AT7 types here:
http://www.audiotubes.com/12at7.htm
