Mod for budget Tube Mics

  • Thread starter Thread starter malcolm123
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Yes, the easiest thing is to change the tube, and can make a world of difference. Get NOS and try several, 12AX7 included. You’ll never know which sounds best to you until you try them.

As Marik said, some of these mics are hybrids in that they use a bipolar transistor impedance matching output stage – not a transformer. That leaves only two other things you can do besides changing the tube: Change out the caps in the signal path or yank the board and install a new one with a good transformer (Royer mod, other Neumann copy, etc…). Here again, different types of caps sound different and different makes of transformers sound different, so you have to experiment.

If you want to try just changing the caps, you can probably make a big improvement by just doing that. Get some same value (larger would be better, but they might not fit) Panasonic polyesters from DigiKey and swap them for the ones on the board in the signal path. MXL and Studio Projects use WIMA (metal film?) caps which are good parts, but I’ve heard from reliable sources that the PPs sound better. They’re much larger, too, so you’ll have to bend the leads up and be creative to make room. If you don’t like them (can’t imagine that) you can always swap them back.

Of course, if you are incompetent with a soldering iron, STAY AWAY FROM THE CIRCUIT BOARD!!! You will lift traces and destroy it! :eek:

But you ask for mods, so here they are.
 
Marik said:
<I think I read once that it was a C-12 copy with some changes. I also heard it was kin to the ADK TT. It's hard to find any real info on it, though.>

I never had chance to listen to this mic, but the fact that Mr. Mao was using Beijin products makes me feel much happier. :)

What can I say? Everybody knows that heart of the mic is capsule, providing that the rest of the circuit is good enough to reveal its qualities. Everybody knows that even C-12VR, which was supposed to be as good as original C-12 in fact was not as good, and it was made in house!
I did not see the guts of CR998 and don't know which capsule it uses, but its price range suggests very good quality parts, considering it is made in China. To say something specific, I need to see it, or to see its schematics.
Click to expand...

Thanks for your response, Marik.
 
Yes,
Thanks Marik. I am starting to get edgy about a possible mod. I just want to learn how my new V69 sounds first in it's original form. Anybody ever modded a V67? How would one go about possible turning it into a Tube mic. I would feel a lot better fooling around with the V67 than the V69. Sh@t <$100 so what the hell.

MAlcolm
 
malcolm123 said:
Yes,
Thanks Marik. I am starting to get edgy about a possible mod. I just want to learn how my new V69 sounds first in it's original form. Anybody ever modded a V67? How would one go about possible turning it into a Tube mic. I would feel a lot better fooling around with the V67 than the V69. Sh@t <$100 so what the hell.

MAlcolm
Click to expand...
I know someone who mods a lot of mics and has done this with several V67s. He says they have the best sound due to the V67's grille, shape, construction, etc. Only drawback is that the body's a little short leaving the less room for tube and transformer.
 
<If you want to try just changing the caps, you can probably make a big improvement by just doing that. Get some same value (larger would be better, but they might not fit) Panasonic polyesters from DigiKey and swap them for the ones on the board in the signal path. MXL and Studio Projects use WIMA (metal film?) caps which are good parts, but I’ve heard from reliable sources that the PPs sound better. They’re much larger, too, so you’ll have to bend the leads up and be creative to make room. If you don’t like them (can’t imagine that) you can always swap them back.>

I like polypropilene Kimber Kaps--they are not very big, and have very good value for money. I converted a couple V67s to tubes. With hard wiring I had no trouble 'squizing' the parts into the body. What really bothered me is MXL logo on the body. :)

Tube mics have an additional advantage--because of presence of high voltage you can change the polarizing voltage on diaphragm, and fine tune it for the best performance.

Also, in some cases it is possible to retune the capsule itself.

Please, please, please!!!
For everybody!
Please do not do anything with your mics, esp. tube ones, unless you know EXACTLY what you are doing. One wrong motion can kill your capsule.
The high voltages in tube circuits may be lethal.
 
Last edited:
<Marik, you and Gus are giving me the "tube mic building fever"!>

:D :D :D

Yeah, I know--I am in pain myself--If we had 25 hours a day...
 
tdukex said:
Marik, do you know anything about the 797 Audio CR998? It does have a 6072 tube. Any known mods?

http://www.797audio.com/web/Frameset.htm

I think I read once that it was a C-12 copy with some changes. I also heard it was kin to the ADK TT. It's hard to find any real info on it, though.
Click to expand...

Just so you know, though the 797 Audio CR998 is suppose to have a 6072 in it, both mine came with a tube (and each one with a tube replacement) with NO markings on them and look to be EXACTLY like my Ruby 12AX7 tube.

I've tried various other tubes in my CR998. Lately, I've been keeping a Mullard ECC83 w/ long ribbed plates tube in there with MUCH success.

By the way the CR998 may resemble the C12 somewhat outside, but it's a whole different ball-game inside... I'll post some large pics of the inside of one of my CR998s real soon if anyone is interested.
 
i guess i'm a little late ha malcolm.. its all good though....
simply by changing the tube in a mic you can enhance harmonics, dynamics, and or the overall sound of the mic..

the can M9 when i first got it sounded great but after looking at its just about flat freq i felt it was missing a little something.. by changing its cheap ass russian tube to a groove tube i heard a boost overall in the dynamics of the mic and the hi end came around...
i can't wait to try a telefunken or Mullard tube in it.. i also happen to use a tube preamp and when i changed its tube the output boosted. i had to tern my gain down b/c it was to high, but with the tube that was in it.. i had a lot of headroom at 40% gain.. now at 30-35% i'm actually tracking louder, cleaner, and it sounds a little more upfront...
 
<I've tried various other tubes in my CR998. Lately, I've been keeping a Mullard ECC83 w/ long ribbed plates tube in there with MUCH success.>

Did you try good NOS 6072? Interesting how you'd describe the difference.

<By the way the CR998 may resemble the C12 somewhat outside, but it's a whole different ball-game inside... I'll post some large pics of the inside of one of my CR998s real soon if anyone is interested.>

I'd be definitely very interested to see its guts, incl. PSU. If you could make clear pictures of both sides of PCB, I could reverse engineer the schematics. What kind of the capsule? Is it Neumann, or AKG style?

<by changing its cheap ass russian tube to a groove tube i heard a boost overall in the dynamics of the mic and the hi end came around... >

Don't forget that GT tubes are just rebranded, with kinda QC, even "cheaper ass" Chinese tubes. Was the Russian tube Sovtek? Electro Harmonics 12AX7 supposed to be better.

<i can't wait to try a telefunken or Mullard tube in it.. >

Definitely much better shot.

<i also happen to use a tube preamp and when i changed its tube the output boosted. i had to tern my gain down b/c it was to high, but with the tube that was in it.. i had a lot of headroom at 40% gain.. now at 30-35% i'm actually tracking louder, cleaner, and it sounds a little more upfront...>

Most likely the tube was either bad, or lost its emission. I have never seen such a drastic change in gain even swaping Sovteks or Chinese stuff for Telefunken smooth plates. There is however a custom of "changing names" of tubes. Very good example would be rebranding EL84 as 7189, although they have very different characteristics. I myself saw Chinese tubes with 12AX7 logo, which looked exactly like 12AT7 and had 12AT7's gain. Go figure.
 
Marik said:

Don't forget that GT tubes are just rebranded, with kinda QC, even "cheaper ass" Chinese tubes. Was the Russian tube Sovtek? Electro Harmonics 12AX7 supposed to be better.
Click to expand...

i heard that from someone else too.. but all i know is my cad M9 sounds great right now. the tube i took out of it i have next to me right now... its a Russian(sovtex) 7025/12ax7wa

i don't know shit about tubes really so enlighten me on this tube if you could please...

as for the telefunken or mullard tubes.. where can i buy some first off? second, which is the right tube for my mic?

i plan on getting the Cad VX2 in the next few months...

the tube in the mic now i got from guitar center.. its a groovetube ecc83 i think.. i have to take the mic apart to see again, but i'm sure thats what it is..
 
when testing a tube.. is a value of 91 good??? i can get a matched pair of mullard's cheap.. i was thinking about on in my pre one in my mic...
 
Here's a kinda silly question, but where would I buy a Telefunken or NOS tube? I've seen some Groove Tube tubes from my neighborhood Sam Ash, but I'm not sure where to get the better stuff.

Es.
 
Marik said:
Malcolm,
V69 is a hybrid design, so instead of output transformer it uses FET transistors.
I would suggest to try a NOS 6072 (it is a very nice tube used in original C12 and ELA 250) in place of Chinese 12AT7. They are pin compatible, so you wouldn't need to do any soldering job.
Click to expand...

Marik,
I found an online tube dealer, but it seems that the 6072 is a 12AY7 tube. MXL lists that the V69 is a 12AT7 tube. Does your suggestion mean that a 12AY7 can replace a 12AT7 tube? Or was that a mistake in the numbers?
 
<i heard that from someone else too.. but all i know is my cad M9 sounds great right now. the tube i took out of it i have next to me right now... its a Russian(sovtex) 7025/12ax7wa>

7025 is a worst industrial "rigid" version of 12AX7 you can imagine for such a delicate application as a mic. It might be OK for guitar amplifiers for certain kind of distortions, but in the mic... considering that it is a no feedback amplifier--no, no, no. Got the hint?

<when testing a tube.. is a value of 91 good??? i can get a matched pair of mullard's cheap.. >

These are twin triodes. How are they matched? Between the halves inside of the tube, or between the tubes (it means that between all the halves)? Anyway, you don't really need 'matching' for your application, and it is probably one of the biggest speculations for sellers to catch buyers. How cheap? You might still get out of them a long lifespan.


<where can i buy some first off? second, which is the right tube for my mic?>

There are a lot of tube dealers you can find on internet--shop around. Also ebay--just check the feedback of the seller and make sure he is not a newbie. Look for NOS (new old stock) ones. The right tube is one which sounds the best to your ears.

<I found an online tube dealer, but it seems that the 6072 is a 12AY7 tube. MXL lists that the V69 is a 12AT7 tube. Does your suggestion mean that a 12AY7 can replace a 12AT7 tube? Or was that a mistake in the numbers?>

No it is not a mistake. You are correct--6072 (or 6072A) is a special lower noise version of 12AY7. As I mentioned before, it is a very nice tube and can directly replace 12AT7 in V69.
 
Recording Engineer said:
Just so you know, though the 797 Audio CR998 is suppose to have a 6072 in it, both mine came with a tube (and each one with a tube replacement) with NO markings on them and look to be EXACTLY like my Ruby 12AX7 tube.

I've tried various other tubes in my CR998. Lately, I've been keeping a Mullard ECC83 w/ long ribbed plates tube in there with MUCH success.

By the way the CR998 may resemble the C12 somewhat outside, but it's a whole different ball-game inside... I'll post some large pics of the inside of one of my CR998s real soon if anyone is interested.
Click to expand...

I haven't looked inside mine, but the extra tube is exactly as you described it.

You say your are currently liking a Mullard. Have you tried an NOS 6072?

I am definitely interested in seeing the inside.

Thanks for the response, RE.
 
how cheap. $20!!!
they were matched using Hickok 600A.. what ever the hell that is

my cousin told me the best tube i can use in a mic for vox is Mullard cv4004.. he said they cost abut $70-100 for a NOS tube....(the cv4004's from 1956)

so what do you think about this statement???
 
Don't have time to respond right now, but I will... I've a couple different 6072s and Mullard CV4004s. Absolutely love em!
 
<how cheap. $20!!!
they were matched using Hickok 600A.. what ever the hell that is
my cousin told me the best tube i can use in a mic for vox is Mullard cv4004.. he said they cost abut $70-100 for a NOS tube....(the cv4004's from 1956)
so what do you think about this statement???>

Hickok 600A is a nice tube tester...
Your cousin is right--the CV4004 is indeed very, very good tube. Personally, I like its sound over Telefunken 12AX7 smooth plate. I think it is a good deal--just go for it. Even if you decide that 6072 sounds better in your mic, it is still a good idea to have it.... just in case.

<I've a couple different 6072s and Mullard CV4004s. Absolutely love em!>

Review and comparison please!
 
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