Mesa Boogie SPAX7 in a Peavey Valve King Head.

[IamME]

Has anyone put the hot rodded boogie SPAX7 tube in the #1 slot on a 100w Peavey Valve King Head (first generation)?

[The Dude]

I haven't, but I'll say this. Of all the tubes I have used, Mesa tubes are the most unreliable. It's been my experience that they also had/have the highest rate of "bad out of the box" tubes. Also know that they don't make tubes. They buy them and rebrand them. My guess? It's somebody else's spiral filament tube for less noise with shrink tubing installed (presumably to help with microphonics- which you could do yourself if you like). I wouldn't pay an extra nickel for one, but that's just my $.02.

And, by the way, welcome to the place!

[Leo_Gnardo]

There's nothing "hot rodded" about SPAX7, regardless of any advertising claims. What they were in the 80's-90's, generally Chinese Shuguang 12AX7 selected for low noise, high gain. They took tubes that tested well, put a piece of heat shrink tubing on the glass, and charged a high price for the time, about $20. If they're still offered, probably same thing holds but they may be from a different manufacturer. At times Mesa has offered house-branded EI (way back when) and JJ (recently) tubes. You'll probably find Sovtek/EH as well, with Mesa paint on them.

[The Dude]

... They took tubes that tested well......

They actually tested them? I find that hard to believe.

[Leo_Gnardo]

They actually tested them? I find that hard to believe.

We'd have to ask the guys that were there at the time, 80's-90's. In more recent times I'm pretty sure Mesa has farmed out their tube testing for better (?) or worse.

My experience with the SPAX's was, they generally were reliable and had minimum microphonic squeal & jingle, although those defects could appear with time as the tube underwent thermal cycling in normal use. Aside from being not garbage right out of the box I didn't find anything special, no super high gain or "tonal superiority." So much for "hot rod" claims.

[axemanvr]

...Aside from being "not garbage right out of the box" I didn't find anything special, no super high gain or "tonal superiority."...

I just bought a set of six Mesa Boogie STA SPAX7-A for my Mesa Boogie TA-30 and so far they have proven to be super quiet and microphonic-free.

As far as tone goes, I did find one to sound comparatively "dull" sounding, so I put that in the phase inverter slot. Otherwise I am impressed with their overall quality. Nothing "special" perhaps, but certainly not "bad" either.

I'm sure you can get a bum tube from them but, from my experience using their other tubes (STA 6L6 & EL84's), I find them to be reliable and consistent. Worth the extra money to me just to save the time weeding out the bad ones from some of the other suppliers...


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[Leo_Gnardo]

Thanks for your report axemanvr & I'm sure others will find it of interest. A couple things I'd like to know, what's in the glass IOW what tubes are presently being marketed as SPAX? If you can't tell by looking could you snap a photo or 2 that have a good view of the tube interior, and show us? And how much are they charging? Thanx in advance!

[bob p]

Now I've seen everything. At first the HiFi people started putting silicone cock rings on tubes ....



then things progressed to wearing gold jewelry ...

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and now people are even using a ghetto version based on a hose clamp...



What's next? Now the tubes are wearing condoms!



But seriously, doesn't anyone realize that the heatshrink tubing is insulating the tube?

[Leo_Gnardo]

What's next? Now the tubes are wearing condoms!

But seriously, doesn't anyone realize that the heatshrink tubing is insulating the tube?

Mesa's been offering SPAX dressed up like that since mid 80's. Yes the heat shrink insulates the tube, maybe it wears out a little faster. One could use clear heat shring, maybe a little less insulating. Shrink on the tube is an old "fix" for microphonics, as are the silicone rings. Sometimes it helps, sometimes not.

Besides the items you've shown there's also heat-dissipating fins. Magic/Ruby used to have 'em way back when. Pearl in Canada may still offer them. I have a pair of EL84 with the fins on, in a Knight kit 10W "hi fi" amp my Uncle Harry built in the late 50's. They look kinda gothic (!) but I swear I get more mileage with 'em on.

Antique used to offer tubes dressed up with sprigs of yarn "hair" and googly stick-on eyes like Mr Potato Head - little works of art (?) for amusement. I don't see them in their on line catalog. They were called "Campy"s and used to be featured in the print catalogs from the 90's & early 00's. Not intended to be energized I guess.

[axemanvr]

...A couple things I'd like to know, what's in the glass... could you snap a photo or 2 that have a good view of the tube interior, and show us?...how much are they charging?

It's virtually impossible to see what's inside without taking the shrink wrap stuff off. Here's the only pict I have of them:



I got mine from Sweetwater for $22 each (free shipping), which is about $7 higher than an average Tung-Sol 12AX7 ($15) so they are quite a bit more expensive.

I am not saying the Mesa tubes are the best thing since sliced bread (I'm sure there are plenty of equally good tubes out there), but I do believe their testing procedures seem to work to a reasonable extent and I have been very happy with their tubes thus far.

Just my 2 cents worth...


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[Steve A.]

I used to do HVAC service and repairs for store credit for the local Mesa Boogie dealer 20 years ago and bought a lot of their tubes. While their power tubes were top notch I found their preamp tubes to be a bit boring, especially the SPAX7's.
I forget her name but their ads back then showed a lady hitting tubes with a hammer to weed out the microphonic ones...

Steve Ahola

P.S. Over the years many people have tried rolling tubes in their Mesa Boogie amps and a lot of them have decided that the stock Mesa Boogie tubes sounded best in their typical amps.