Are "mismatched" 12a*7 tubes OK for microphones? A

I am interested in getting some alternate tubes for an ADK TC and Nady 1050.

Highly regarded tubes can cost a lot, so I am wondering if a "mismatched" tube (which can be had for significantly less $$) can be used in a microphone. I suspect that this might depend on the circuit involved. I don't have the ADK circuit schematic, but the Nady 1050 (ie Apex 460) circuit is readily available here: http://www.apexelectronics.com/pdfs/smapex460.pdf

Honestly, I don't even know exactly what mismatched even means, but here is an example of what I am talking about (from https://www.tubeworld.com/index_high.htm ):

"1 Low Noise Tube $35) E81CC=12AT7WA Siemens NOS triple mica 1971 triode sections mismatched 15-20%"

"1 Low Noise Tube $50) E81CC=12AT7WA Siemens NOS triple mica 1967 original box"

Obviously, I am just starting to learn about tubes, so if anyone could give me a link that might answer this sort of question, I would appreciate it. In addition to finding out whether or not I can save money buying mismatched tubes, I hope to gain a bit of knowlege here. I have a bit of electronics knowlege, but I don't know anything about tubes.

Also, if anyone has any advise on buying tubes, please feel free to chime in as well.

One thing that I want is to be able to make the microphone sound more "tubey"--that is to have more agressive tube coloration. Both the ADK TC and the Nady 1050 that I own sound similarly clear. While I would certainly love to have a tube that makes either of these mics even "more clear" (more headroom, less noise, better high frequency extension, etc.), I would also like to have tubes that make the mic more agressive sounding (eg. for male rock vocals).

You might want to check out E-bay for Tubes as those Prices you quoted seem very expensive...For the price of one of those tubes you could buy probably 5 or 10 tested Good tubes on e-bay.....


Take a Look :

http://search.ebay.ca/search/search.dll?MfcISAPICommand=GetResult&ht=1&shortcut=0&from=R41&query=12AT7&category0=&Submit=Search


The Mismatched probably means that the Sections of each Triode don"t match with the other triode as these are Dual Triode Tubes....

I don"t think that Mismatched tubes would be a Problem with a Microphone but would be if for instance each triode was being used in 2 seperate channels of an amp as they wouldn"t have matching Gain, But I"m not really a Tube person so I could be wrong....

Good luck

Section mismatch is not not important. These circuits usually use the second section as a cathode follower (if at all).

Consider changing the tube to a 6072a. If you aren't changing the transformer in the mike, this will result in improved ability to handle high level input (due to the slightly lowered gain). I have found that if you buy 2-3 ElectroHarmonix 6072a on ePay usually for around $10 each that you will find one that is very good for use in this type of mike.

Mis matched would hurt in a push-pull or phase splitter,
where you want each half of the wave aplified by the same amount to cut down on
distortion, but a mic circuit should be OK.

Wow,

I am amazed that I got responses so quickly. Thanks guys. I definitely intend to try out several different kinds of tubes--inculuding a 6072a

I have done a lot of searching on ebay--in fact, I have already won a few auctions for tubes (one of them for 99 cents)! However, I am potentially interested in purchasing a tube or two from a dealer that can do noise testing (not provided for any cheap tubes on ebay) as well as provide guidance. Note the comment about having to purchase 3 ebay tubes in order to get one good one. Tubes purchased from a dealer such as TubeWorld can be returned--not really an option for most ebay auctions.

Thanks Again,
Tommy

http://www.groupdiy.com/index.php?topic=256

stuff with the 1050 can be found. A lot to read but some good stuff.

don't believe the stuff on the web with the nady and apex

Test it yourself

Do you have the microphones? The 1050s I have had the tube soldered to the board.

What is tubey? Tube microphones tend to be clean the transformer and capsule are a different story

Thanks Gus,

I have previously read about modding the 1050 (including your posts). I suspect that I have a newer version of the microphone, but I have not yet checked to be sure that it has a socket.

In any case, I may have dim ears, but honestly, the sound of my microphone (currently 100% stock) is very respectable--to me it seems just as good (at least on male vocals) as my ADK TC (which I bought used on ebay) and AT 4050 (which was a factory refurbished model). Of course, maybe the problem is that my other mics are not particularly great specimiens so all I know about is crappy sounding mics.

What I mean by tubey is a more agressive sound--more like a guitar amp, less hi-fi, more 1950's than 1990s. Of course the iconic microphone example from the 50s is the U47, but I suspect that a U47 would be cleaner than what I am talking about.

You might like the stock transfomers in the microphones with a different tube.

As posted by burdij try a 6072a/12ay7 in the 1050. That tube will have better operating point than a 12ax7 or 12at7 in that circuit. A simple and good change. Look for a GE 5 star 6072a or GE 12ay7.

Next maybe try removing the CF in the 1050. Then cap changes.

I have not seen a ADK TC

I just checked and neither the ADK TC nor the Nady 1050 have tube sockets. I think that with a bit of work, I could get a socket to fit in both. The Nady is going to need a PCB mount socket, while the ADK needs a free standing one. If anyone knows the best place to get a small tube socket, please mention it, but I will be searching around.

Thanks,
Tommy

Sockets can be obtained from Antique Radio Supply

http://www.tubesandmore.com

They have a ceramic 9 pin that is similar to the socket used in the Apex460/Nady1150. On sale, now, for 1.76

Another source for sockets is New Sensor

http://www.newsensor.com

You might need to create or modify a mounting bracket for the socket

just wonder why mismatch shouldnt be a problem...especially in a microphone thats at the beginning of the recording chain...
Maybe because some people dont need headroom and love noisefloor and distortion?

3phase:

I invite the experts to explain it better, but as far as I know, think the both halves of a 12a*7 in the microphone are used as 2 separate tubes doing different functions, or sometimes just one halve in use... so why do you need both halves matched?
:wink:

Synthi

ups.. i thaught they wanted to replace the tubes with different types...

Somewhere in the 1050 thread there is a post with solder in pin sockets for the 1050
the small pin sockets solder to the board and a tube can plug in and fit.

found it
http://www.groupdiy.com/index.php?topic=633

Thanks Gus.

I was not able to see the pics on the thread, but I did find this "socket saver":

http://www.tubesandmore.com/scripts/foxweb.dll/moreinfo@d:/dfs/elevclients/cemirror/ELEVATOR.FXP?item=P-ST9-900

(Also on ebay.)

I think the main difficulty is going to be fitting the tube in on top of the socket. I may have to move the entire circuit board up a bit.