Thanks for the cue, stokes! I was going to stay out of this one, but oh well...
If you have a head, I'd go ahead and start stocking up on some used VOS or NOS tubes.
My fave is the euro-not-trash-for-thrash Philips family of shortplate 12ax7's, fave is Siemens shortplate 12ax7, Amperex, not necessarily bugle boy, Mullard, Philips Miniwatt...Spendy! :shock:
If you have a combo, I'd stick with less expensive new production tubes for other than V1. The reason is that your amp design is so powerful and loud that loud noises with tons of gain and bass really rattle the tubes around. That vibration can expose any microphonic tendencies very quickly and shake tubes to death, vintage or new production! That is the reason Jim Marshall went to the head style of amp construction. :wink:
Your idea about using that vintage military tube in V1 is good tonally. However, just because the tube says 12ax7wa (the "w" stand for military issue) doesn't mean that the tube will resist microphonics all that well. As a matter of fact, I have some brand new NOS Hentz and Kaufmann 12ax7wa's that are microphonic right out of the box, they are relabeled Sylvania long grayplates, very similar in design to what you are asking about.
For what you are looking for I have one sure fire recommendation, RFT 12ax7. They are among the most resistant vintage 12ax7's to microphonics and they do a great dirty tone. Not inexpensive! They can be a bit darker than some, but you have the tone stack in your amp to compensate. Another tube that will be affordable and is very well made is the Matsushita 12ax7 with 45 degree getter flash, the "Japanese Mullard." Expect to turn down the treble and especially presence knob (if your amp has one) 2 to 4 notches until you get a thousand hours on them, they can rip your face off at high gain settings, but the bottom and lower mids are strong on that one. Have a few of those in yellow print Raytheon labeling. Needless to say that one will cut through the mix like a chainsaw running on Nitro! Very resistant to microphonics in my experience.
It is true from my experiences that long plate tubes tend to be, but not always, more prone to microphonics than short plate designs.
I think that Elecro-Harmonix 12ax7's have the right construction to resist microphonics, but you will have to get several and weed out the crappy ones, same with the TungSol reissue. The winged C silver box plate 12ax7 is hard to find but has metal tones in it. They can get microphonic too. Stay away from EI 12ax7's...they have long plates and flimsy micas unless you find some with doubled micas top and bottom, some of the military ones have that type of construction, not sure about the Mesa labeled ones. The so called silver bullet of theirs is not suitable for the flimsy mica reason.
Another great vintage old stock tube for your needs that resists microphonics well and sounds great cranked way dirty is the GE 12ax7a/7025a short grayplate. I'd choose that over the JAN Philips based on the microphonic resistance thang. That is going to be the main hurdle, microphonics at high gain and volumes if your amp is a combo.
And finally, GE 5751's sound great, resist microphonics well as a general tendency, the gray plate 5751's are affordable. You can probably get enough gain from your circuit even when using 5751's. Vintage 5751's have a gain factor of 70, about the same as a Sovtek 12ax7...!
If there is a slightly microphonic tube that I am really attached to, I get a couple of pieces of one inch heatshrink tubing, placing it a la mesa where the bottom of it will clear a tube socket skirt that the metal tube shield attaches to, and shrink the two layers on top of each other all the way up to where the top starts curving inward from the side of the bottle. Helps some, but not perfect, at least it's an inexpensive help...and don't worry about whether the tube shield fits over the now fatter tube, I have never heard an improvement in tone when using them, as a matter of fact the tube will just cook inside them and last not as long. If you don't have heatshrink tubing on the side of your tubes and you want longer life, check out the admittedly tech-weenie and somewhat boring post on IERC shields in my Maverick...Your amp might be different than mine as far as whether the stock shield is of help for overall noise reduction, however. The Mav does not shield its 12ax7's at all, I was using them for the el84's that run really hot in that amp design. End of commercial... :wink:
I get nearly all my vintage tubes on eBay, and expect up to a third of your transactions to result in less than perfect results for what you want and be happy as well as forgiving of sellers, there are a lot of folks selling tubes that are pretty ignant of guitar amp needs. Be generous with the 5 star feedback thang, cause if you aren't the only sellers on ebay won't be the mom and pop guys, they'll be all the big businesses we love to hate. The new feedback system of theirs really hurts the sellers. I liked the more level playing field of the old system...end of rant.
Peace. 8)
I'll stand by my post as well, and what is important is that a microphonic tube just ain't musical while all that howling and or screeching is going on, and chances are that the offending tube will be yanked out of a high volume, very high gain situation long before it dies. Stokes, you are one of the good guys here and I have tremendous respect for you and your words.
