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Mesa's SPAX7A preamp tube

Posted: Wed Jun 13, 2012 4:13 am
by sevycat
Anyone used these and do you have to remove the rubber shield before putting them in the preamp slot? I am wondering if the heat of the preamp tube would melt the rubber shield on that tube.

Re: Mesa's SPAX7A preamp tube

Posted: Wed Jun 13, 2012 3:00 pm
by MrMarkIII
The rubber shield is permanent and designed to prevent microphonics.
I suppose you could remove it, but it's usually safer to leave the rubber on.

Re: Mesa's SPAX7A preamp tube

Posted: Wed Jun 13, 2012 3:22 pm
by benjamin801
MrMarkIII wrote:it's usually safer to leave the rubber on.
Words to live by. 8)

Re: Mesa's SPAX7A preamp tube

Posted: Wed Jun 13, 2012 4:58 pm
by sevycat
benjamin801 wrote:
MrMarkIII wrote:it's usually safer to leave the rubber on.
Words to live by. 8)
Hahahaha! That was funny! Thanks folks!

Re: Mesa's SPAX7A preamp tube

Posted: Wed Jun 13, 2012 6:35 pm
by screamingdaisy
They've been on mine for years and the rubber's never melted.

Re: Mesa's SPAX7A preamp tube

Posted: Thu Jun 14, 2012 8:33 am
by benjamin801
screamingdaisy wrote:They've been on mine for years and the rubber's never melted.
Yes, the serious answer is this. Unless something is going wrong, preamp tubes really never get very hot to the touch, let alone hot enough to melt rubber.

Re: Mesa's SPAX7A preamp tube

Posted: Thu Jun 14, 2012 10:27 am
by MrMarkIII
Yes, be serious. It takes a lot of friction to melt your rubber.
Harrumph!

Re: Mesa's SPAX7A preamp tube

Posted: Sat Jun 16, 2012 7:09 am
by stokes
The SPXA7 is supposed to be quieter than other AX7 tubes.The only thing that makes it any different is the rubber sleeve.Leave it on.I tried one,thought it sucked,wasnt any quieter in the V1 position,in fact I have many preamp tubes that are much quieter.Not worth the extra $$ for a Russian AX7.

Re: Mesa's SPAX7A preamp tube

Posted: Sat Jun 16, 2012 10:24 am
by MrMarkIII
stokes wrote:The SPXA7 is supposed to be quieter than other AX7 tubes.The only thing that makes it any different is the rubber sleeve.Leave it on.I tried one,thought it sucked,wasnt any quieter in the V1 position,in fact I have many preamp tubes that are much quieter...
...And where might these be purchased?

Re: Mesa's SPAX7A preamp tube

Posted: Sat Jun 16, 2012 11:16 am
by stokes
I've spent 30 some years finding and culling NOS and old stock tubes.I have a fairly large collection.Between my sons and I we have about 20 amps,most built by me and they should never have to buy new tubes for any amp after I'm gone.My point was,that the SPAX7 that Mesa sells as a quieter tube,for more money, is not necessarilly worth the $$.The rubber sleeve is just there to insure any slight microphonics,which is present in any tube,is kept quieter by the damping effect.Get some appropriately sized heat shrink tubing and you have a SPAX7.They just test them to be sure they arent overly microphonic.I'll bet the ones that display microphonics to an undesireable degree are then sold as "normal" 12AX7's.When you buy one of those noisy preamp tubes,they then tell you to buy a SPAX7.Brilliant marketing,which,in my opinion,is all that Randall Smith was innovative about.

Re: Mesa's SPAX7A preamp tube

Posted: Thu Aug 23, 2012 10:53 am
by 212Mavguy
Stokes words,

+1, right on.

Re: Mesa's SPAX7A preamp tube

Posted: Sun Aug 26, 2012 4:07 pm
by stokes
Hey,Mav.Been a while been pretty busy myself,hows things by you? I had a guy bring me a couple real sweet old Fenders,a Brown Deluxe a Brown Princeton,two real clean amps.A 57 Tweed Tremolux that was a mess,but we got it in order,and the absolute cleanest 57 Tweed Champ I've ever seen.This thing belongs in a museum.Looks like it just came out of the box.Except for a small scuff on the Tweed,it looks brand new.The chrome is spotless,circuit board is as clean as I've ever seen.Its the first time I just couldnt bring myself to re-cap an amp.Told him to sell it and get something he could actually play.This amp works well,isnt really any noisier than you could expect from an amp that age,but with those original caps I told him he should just leave it to someone to look at.I'll try to find and post the pics I took.Gotta see if I can figure out how,computers are still foriegn to me,ha.

Re: Mesa's SPAX7A preamp tube

Posted: Fri Oct 12, 2012 7:56 am
by 212Mavguy
:shock: HIJACK ALERT :shock:

Stokes!

Funny you should write to me about vintage re-do's. I have purchased three Dumble clones, my 2/12 Mav gets little use now, nice as it is, it's for sale at a not cheap price, but the thing that has changed the most is my learning more amp theory and having fabulous luck on redoing three 60's Point to point/terminal strip vintage Sound Projects made in the USA amps.

'61 Harmony H-306A 1/12 combo (5y3 rec pair of 6v6 2-12ax7 1-6sh7 for bias modulated tremolo, a Lectrolab R600C 1/12 combo (same amp/circuit type as H-306A, EZ81 rec, pair of el84's, 2- 12ax7's and this time a 6au6 for the bias trem, and a Harmony H-420 1/15 (direct sibling of the Supro Thunderbolt) combo.

These are originally wired just like today's top end boutique amps. I replaced/massively increased power supply filtering, yanked out the crappy original tone caps, (saved 'em in original condition) replaced them with Paper in Oil cold war commie caps from a seller in the Ukraine, retensioned the sockets, replaced old stock glass with newer sounding old stock glass, yanked all the original speakers and replaced with:

H-306-A Altec 600b original cone for the original Jensen p12r
H-420 JBL MI-15 NOS for the Jensen c15ps
Lectrolab R600C vintage stereo cab pull Pioneer 12 inch woofer with parabolic cone and 2 " VC for the original Jensen c12r. That speaker is the tweed era Jensen P-series speaker killer of all time.

These amps were originally built with a well balanced selection of cheesy parts. When the right parts are placed in circuit and decent speakers installed to express the circuit, they are some of the most amazing sounding amps I have ever heard, and that's from an owner of three Dumble clones, a Bluesbreaker clone a Boogie, Hiwatt DR504 clone running bendix 6384's and on and on sorta like yur collection, I only have 13 amps. These three sound Projects amps are not especially loud, but all have a shimmer on the top end, all sustain unusually well, all have huge warm fat full bottom and lower mids, The el84 and 6v6 amps are my "stereo blue angel" rig, with a 6v6 amp on one side and similar amp running el84's on the other the sound is huge, hit the footswith for the deeply throbbing trem and the noted just hang, shimmer, and growl in the most amazing way, these amps throw out an amazing amount of even order harmonics, something that push pull designs aren't supposed to do, but these designs, not being Fender based, have non Fender tone palettes that are PERFECT for small and medium clubs. Hit the front end with a lot of eq pedal/boost with the amp volume knobs serving as master volume. These amps will sing forever at smaller venue volumes with no noise complaints from the bar or sound man or club owner, fat full rich, chimey/snarly on top.

I'm not buying any more new amps, from now on I'll be rebuilding or scratchbuilding my new stuff. Got a couple books and an online forum to learn from and have taken advantage of it. After doing these three up in the last three months smelling the solder fumes and then flipping on the power switch for the unusually successful results I'd get cocky except that I know I did some easy ones.

Re: Mesa's SPAX7A preamp tube

Posted: Fri Oct 12, 2012 11:18 am
by stokes
Sounds awesome.Who's the guy in the Ukraine?I got a box of those "cold war caps" from a guy in the Ukraine,wonder if its the same guy.Cant remember the name,its saved on my home computer.I tried some of his electro's that seemed to be okay,about 2 yrs and they crapped out.Luckily they were in my own builds that my sons put thru the motions for me,so I didnt end up using them in customers amps.Stay away from them,if you havent tried them yet.The coupling caps are doing fine,been using them for over 3 years now.

Re: Mesa's SPAX7A preamp tube

Posted: Fri Oct 12, 2012 12:49 pm
by 212Mavguy
No 'lytics. Just tone caps, K40Y-9 and k42-Y, using 400v and 630v ratings. Several vendors on ebay have 'em. Their version of "Sprague Vitamin Q." Superb sounding, affordable, made a big difference from the stockers. Much more musical. Commie caps great bang for the buck...easy to find, los of 'em. Commies historically better at making guns than butter...so use the stuff originally designed to help kill people to make music with, I say.