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In Reply to: RE: The 12AX7 closest to the vintage Mullard posted by ElWoodrow on April 05, 2014 at 07:50:36
when people talk about vintage Mullard 12AX7's
My earliest Mullards are mC1 long plates
Second vintage sre f91 long plate
Third are f92 long plates
Each of the above sound quite different
The short plates include
I61
I63
I65
Then there are CV 4004's box plates, All Mullards dating from 1954 through 1986
There maybe more, but I haven't really tried to collect all the variants as I prefer the long plates....
So what Mullard is the one which rocks your boat?
So when talking about viontage, what Mullard are you talking about
Follow Ups:
Yup, there be many flavors of Mullard 12AX7's. I have never heard the original long plate 12AX7 but I have a pair of MWT labeled LP 12AU7's and they are excellent in my Decware Mini Torii.
Stu, think most ppl associate vintage "Mullard tone" with early 1960's long plate (17mm?). Those type seem to have similar tone. Is that your experience?
Thanks!
There are three different long plates that I know of:The acid etched codes are mC1, f91, and f92, IME there are distinct differences in sound. The mC1 is IIRC 1955 through 1957. F91 from 1957 through 1958. F92 from 1958 through 1959, and then IIRC the short plates arrive. mC1's usually have a D getter. f91 have a metal staple on the top mica across the plates with a short white coated wire touching the grid. The f92's has the extra mica sheet to cover the cathode.
There are overlapping dates and sometime I find an f91 labeled mC1 and f92 labeled as f91... making it even more confusing.
mC1 are very lush and warm, f91's have a very open upper midrange, f92 is very even but not as detailed as the f91, which ranks as one of my favorites.
But the point is these are three distinct sounding tube types..
Edits: 04/05/14
Picture of f91 and mC1 from 1957 - Mullard Blackburn
Edits: 04/06/14
If you look very carefully at the left tube, you can barely make out the staple protruding from the top mica sheet holding that little white wire I was trying to explain. The wire is more visible on the left side plate in the photo.
Any one knows its purpose?
Seems a lot of extra assembly steps to install that wire. It is welded to the staple on the mica top but only gently touching one of the grid posts. In fact I have one sample where the wire is installed but not touching anything, so I know it is not welded to the grid post.
It looks like a piece of filament heater wire, but, even if so, I can not figure what its intent was.
Thank you for the photo
Stu
Huh, interesting. I've got some mC1, f91, box plate CV4004, and either a I61 or I63 short-plate in my stash. Haven't listened to the mC1 yet (rare, and I've only got the 1 pair). The f91 is amazing; it's the only Mullard 12AX7 I've run in my amps for long durations -- once they go in, they tend to stay awhile (and they're in there right now). I've probably spent more time running this tube (in the phase inverter slots of Rogue Apollos, the most important rolling slot in those amps) that any other 12AX7 now.Your description of the "very open" upper mids is accurate. This tube is very clean and detailed (but not bright); a wonderful sound. Better dynamics than any 5751, and with a clarity/focus that approaches the good TM BP 5751 variants. It has a wonderful midrange without the syrupy thickness and heavy-handed warmth (even wooliness) of the box plate and short plate Mullards. The box/short plates don't last long before I tire of them -- usually I end up fixing whatever was begging for the extra warmth.
Now, I'd assumed the long-plates would all sound similar, which seems incorrect by your experience...interesting.
Edits: 04/06/14
Your experience mirrors mine. which I find frustrating because I see so many new tubes being advertised as copies of Mullard Long plates, and, well, which one are they emulating?Most people don't even know about the f91's, and even fewer have noted the construction differences.
Incidentally, I am searching for a cheap, below normal range , or even broken f91 so I can dissect it and examine the insides more carefully. That little white coated wire looks like a piece of filament wire but what in the world is it doing touching the grid posts and not touching anything else? I'm not dissecting my working tubes.......
Edits: 04/06/14
Stu, I think that when most people talk about vintage Mullard 12ax7s, they are referring to the I61 or I63 short plate versions made in Blackburn. Still fairly common to find in good shape, I find these quite warm and rich in my amp (the Mullard sound?).
The I65 were all made in Heerlen Holland I believe although I am sure many ended up with a Mullard label (cross labeling being rampant at the time). Still I consider these Amperex (same as Bugle Boys) not Mullards. The long plate series are far rarer to find these days, I don't think that many people these days have actually heard a pair of the same type in good shape.
is correct.
Philips of Holland owned Mullard, and bought them out in 1927, quiite a while ago.
Theoretically all the Philips factories followed the same blueprints for tube design. This would be particularly true for the 6DJ8/ECC88 types, but funny how all the different Philips plants sound a bit different (as Coors would say, its the water.....)
Incidentally I have seen mC1 with a Heerlen designation, IIRC. It was on Ebay and I could barely make out the acid etched code in the photo, Didn't buy it and didn't inquire any further either. IIRC I have a few I65 with Blackburn factory codes, but I'll have to double check
Curious and I will have to repeat my experimentation to rejog my memory, but IIRC, the Heerlen I's sound different from the Blackburn I 12 AX7's. As memory serves me the Heerlen version always sounded a tad brighter than the Mullards for some reason.
Its like 5751 and comparing Sylvania's to GE's. The Sylvania's consistently sound a bit darker than the GE's even though the internals almost seem to be identical.
Stu, my experience mirrors yours on the Blackburn/Heerlen tubes.
I'm sure you're right about the sound.
I was only committing on the "cross labeling" and wondering that since the plants were owned by the same company if it's really correct to call it cross labeling.
No biggie.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Tre, it looks like nothing has changed. Look at the variations in the Shuguang Treasure and Psvane tubes. The Russian new production has changed over the years. SED Winged C's are now NOS.
"The I65 were all made in Heerlen Holland I believe although I am sure many ended up with a Mullard label (cross labeling being rampant at the time)"
At the time there were a lot of RCA's sold as GE's and GE's sold as Sylvania's, etc
But when one company (Philips) owns both plants (Blackburn and the Heerlen plants) is that really cross labeling?
I guess it is, but in a different way.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
How do any of these compare to, say a black glass National Union 6sl7?
I know the 6sl7 has less gain but in my circuit it's less than 3db and of no real consequence.
I could give you my opinion but I'd like to hear yours.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
no national SL7's, plus I never compare tubes outside of their series.
"... I never compare tubes outside of their series."
I not sure what you mean.
The 6sl7 and the 12ax7 will work in the same circuit (if care is taken) with the help of an adapter.
It's not like I'm comparing (or asking you to compare) apples and oranges.
How about a 12au7 vs. a 6sn7? It's, in a way, the same kind of thing.
BTW You never got back to me on the grounded tube shield causing (if there is capacitance between the plate and the shield) shunt capacitance issue.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
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