12AX7A or is it

Yes!!

I would have thought it would have been a 6072 in the AKG mic.


If it's really a 12AX7 then you can probably try any of them.

Do you have a schematic? If the circuit is Cathode biased then you can just plug and play.

That circuit may actually require a bias measure and fine tune adjustment for each tube, so you should try to find out.

With microphones and the hi gain associated you will appreciate a tube that is very low in noise... so usually a mic tech will try several tubes looking for the lowest noise. It has to be quieter than something that might work good in a guitar amp. So, it is the difference between good and very good.

You will also see that various tubes have very slight to dramatic different response in both frequency and dynamics.

It's hard to think that a brand name recommendation will serve you better than trying what you can find easily.

A new Russian Mullard?

A old RCA 7025? 

Early 1980's JAN Phillips ECG?


Why do you think your old tube is bad?

Some of my favorites that I play in my guitar are 60 years old and going strong.



In any event, you probably live in an area that has a highest tube mic tech per capita ratio so you are gonna be ok.

:-)

Good Luck.


best regards,
mike

bapu

Mesh


Yes!!

Bapu: Mesh, should I get Vanilla or Chocolate?
Mesh: Yes!!

I forgot to add....just giving it a friendly  
 
Chocolate for me please....Yes!!

McQ, as I examine the circuit board the tube mounts on I see no evidence of a any adjustment pots of any kind.

I "think" the tube is going in that the mic seems to record a mild by concerning distortion in the same signal chain that I use for my  AEA R-84 (sans Ribbon switch engaged on Grace M-101 preamp). 

Now that I have the tube out, I guess I should have it checked before plopping down $20, $30, $60 or $160 on some panacea of tube glory, no?

Yes, I just read the owners manual.

Plug and Play.


Have fun with it.

You can search out special model, vintage, pedigree tubes etc. or just try some.


The 12Ax7 was not used in vintage microphones because it is, generally speaking, noisy compared to those that were more commonly used.

It's fine in systems that use less gain and don't need super low noise floors, and so you see it used in guitar amps and radios and some hi-fi.

The 7025 was the label used for 12Ax7s that were culled out because they were low noise.

There are several brand of NOS 7025s. RCA, Amperex etc. that you might try.

Some of the relatively new, made in USA JAN Phillips ECG stock from the early 1980's were pretty low noise.

The various Sovtek brands can be nice, but the consistency seems varied... you have batches of good and batches of YMMV.


Try a few cheap new Russian or Tesla tubes and maybe an old 7025 and one of the 80's JANs.

I'll bet you'll hear differences and I wouldn't be surprised if you find one that sounds smooth but ends up having more noise than another that may not sound as smooth.

Stuff like that.



best regards,
mike

Tubes-valves, and who makes them have changed massively in 15 years. I'd ask AKG who they recommend. The plate and grid voltages of a vocal tube are going to make or break the mic. I garauntee that tube is done. For a vocal mic, a usual guitar preamp tube-valve might be a little harsh. If you can even find any speciality tube makers these days, the ones filled with argon gas were good for vocals. But hey, ask AKG, ask Groove Tube, Ask Sovtek, etc. You'll get a different answer from each. 

ampfixer


Bapu, that's a Chinese 12AX7. Don't waste your money on any of the current production tubes with gold pins and don't stray too far from a 12AX7 if you want to substitute something else, ie, don't go with a 12AT7. Even though people will tell you they are interchangeable, it's a bit misleading. The circuit in the mic is tuned for the 12AX7 bias needs, plate dissipation etc.

Mullard, Tung Sol, Gold Lion, Electro Harmonics and Sovtek are all the same company. The tubes are all different to some extent but they're all Russian. JJ is eastern Europe and then you have all the Chinese stuff.

If you want to try for different sound, go for a different plate structure. JJ ECC83 would be cheapest, followed by Sovtek 12AX7 LPS (large plate with spiral wound filament for low noise) and if you want something high end get a JAN GE 5751. JAN Phillips are also available but trust me, the GE is better for the same money.

If you want a real killer 12AX7 and have deep pockets, do a search for the Northern Electric 12AX7. It's made in China but was commissioned by some friends here in Canada. They spent a couple years working with the Chinese to get the tube on the market and get it right. They are great in mic's and guitar amps. I think they are about $60 but come with an extended warranty.

I could tell you more but eventually I'll violate the TOS. Should you decide that you want Amperex or Mullard pm me and I'll try and hook you up cheap. DON'T pay some dude $200 for a Mullard or Bugle Boy unless it's for bragging rights.

There's the skinny!

mike_mccue


John, 
Isn't the 5751 a lower gain tube that swaps out readily in most 12AX7 applications? Smoother sound but less gain?


Do you have a line on English Mullards?


best regards,
mike

Are the Mullards even still Mullards? Or have they been licensed off to a Chinese factory somewhere? It would be interesting to know why tube-valve makers in the European countries did not survive, and why the magic has somehow deminished. 

You need to bow before the Tube shrine first Bapu.  (Apologies in advance for the DD tubes in the corner.)

craigb


You need to bow before the Tube shrine first Bapu.  (Apologies in advance for the DD tubes in the corner.)

Look at those Rubys.
 

Don't ask how much I paid for some of the Mullards I have... *Sigh*

 
Hey, you know, I bought some Golden Dragons once that sounded great in a guitar amp- tube preamp after a lo0ng drawn out repair sequence. I sent the amp back for repair or replacement at the third juncture and they sent me a different amp with worn out speakers and no Golden Dragons. I couldn't get two more Golden Dragons. LOL. Tube Tech... where has it gone?

Well,... flavor is everything when you're melting a Tootsie Pop. All the flavors are Tootsie Pops but they don't taste the same till ya bite em. It was a rainy day and the room felt like a cloud. We never found that feeling again, I don't know why.

I had an in-law that worked at the RCA manufacturing facility in NJ from the 1950’s through the 1980’s.  A few years ago I had to clean out a storage shed and took home boxes of tubes.  My understanding is that she worked on the line that manufactured tubes and my guess is that she did quality control work.  Many of the tubes appeared new … no boxes, these were off the manufacturing line … with notes written on them with wax pencil.  When I first acquired them, I borrowed a simple tube tester from a guitar player friend of mine and every tube I tested, tested good.

I still have a pretty big box of TV and radio tubes but, I gave most of the guitar pre-amp and amp tubes away to friends.  I still have these two 7025’s.  Age wise they can be anywhere from the 1950’s to the 1980’s.  The hand lettering in red on one of them says 73 18-5 and the hand lettering in green on the other one says 74-E-1.  I suspect they came off the production line, got tested then went home in a lunch box.

They are all yours if you want them; I also have a 12AU7A, a 12AZ7 and a 12AV7.

Wow, now THAT'S a nice gesture!  It's not often someone offers up a couple hundred worth of quality tubes for free.  (I guess those subliminals you've been putting into your songs are paying off now Bapu!)

ampfixer

mike_mccue


Notice the word "English"? :-)

The new official Mullards are to the best of my knowledge from the Russian Sovtek factory.

I was asking John if he had any of the Blackburn Mullards, or perhaps some from a plant in Canada using Mullard tooling.


best regards,
mike

I don't consider current production Mullards or Gold Lion tubes to be genuine. The names, logo's and artwork were all purchased several years ago. They're all Russian. The Mullard tubes I have are a mix of tubes made in England and maybe Canada. I really go by the internals and don't pay much attention to the screening unless it's markings that are etched into the glass.


Ruby, Golden Dragon, Valve arts and Groove tubes are all resellers that buy wholesale and put on their screening and sort according to their standards. Ruby seems to have one of the best screening programs, while groove tubes is something different.


Next week I'll be working on some online reviews of different 5751 tubes and the EF86. Since one of my amps is built around these tubes it easy for me to test and review. If you want to read other stuff just Google - John Templeton tubes.

:-)
Aw come on, the box says Mullard right on it. ;-) :-)




Here's a part of my personal stash of 12Ax7s:








I was afraid I was gonna run out so I started accumulating them about 30 years ago and I still have the urge to get more. 


When I fix an amp I source other tubes for the player... I need these for myself. :-)


I like the for real English Mullards... they actually seem to offer a stronger low frequency response than many other 12AX7s. But they are sort of expensive to buy now a a days.

John, If you are sitting on a big stash of Mullard 12AX7s... PM me... I'm cheap but I know quality!!! :-)


Here's some spectrum analysis read outs I did a couple years ago using a REAMP to play the same very guitar riff through the very same mic, in the exact same position with the exact same preamp and preamp settings. All I did was swap a tube, let it warm up and run the test.








I was surprised to see that the reputation for the Mullard tone could be somewhat substantiated through experience. 




Tube sound characteristics are heavily dependent on the circuit they are working in... so it's not realistic to speculate how a tube will sound in some other circuit but it's lots of fun!






BTW, John Templeton, I've been reading your reviews since before you were a forum member. ;-) That's why I recognized you when you started posting. They are great reviews. I'm still working on my stash of "NATO" tubes so I haven't needed much info about the SINO or ex-Soviet tubes but I find it to be great reading and it's re assuring to think that people are paying attention to tube production with enthusiasm.



best regards,
mike