Swap Tubes In Your Tube Microphones

Brandon Drury —  March 7, 2008

Soundelux U99 Tube Change
Recently, my Soundelux U99 has been acting funny. It’s been VERY noisy and just not sounding right. It’s hard to explain, but it just sounds less pleasing that it did before. I figured I could ship it off to some guy that’ll charge me $400 just to tell me that I have serious problems that are going to cost another $400.

I figured that it was time to try putting a new tube in it. So I did some research and found out that the Soundelux U99 uses the EF86 tube, whatever that means. So I hopped on some tube website. I figured that since I already blew so much money on the Soundelux U99, I should get as good of tube as I can afford. I ended up selecting a NOS Mullard EF86. It cost me about $75 and then I paid an extra $10 to get a “better” tube which I assume is either a rip off or a guy that actually checks the tubes somehow to ensure quality. I don’t know. I’m brand new to this tube swapping business.

The tube came in and said “Hmm. I’m either going to destroy this mic which costs the price of a bad boob job or I’m going to come out with the kind of knowledge where I can write a blog”. (Of course, I’d be writing a blog if I had destroyed my mic, too!)

I unscrewed the base of the Soundelux U99. The metal body / pipe looking thing slid right off. There was all the electronic guts. I had forgotten just how simple microphone circuits are. (The 1% of electronics knowledge I have retained since my days in college nearly 10 years ago kicked in). There was the tube in plain site. I pulled the old one out and put the new one in. I’d say this process took all of 15 seconds.

I put the metal pipe housing thing back on and screwed the base in until it was snug. I plugged the mic into the power supply and fired it up. 15 minutes later I came back and listened through some headphones. I had used this mic for some voiceover stuff over the years. NEVER has it sounded so good. I mean it! I DON’T get excited by little gimmicks and tricks very often. I’d like to think that I’m a little less susceptible to the placebo effect as other engineers (may tend to be obsessed with the placebo effect). It was flat out obvious that this mic sounded like a $2500 mic should after putting a Mullard EF86 in it. I am IMPRESSED!

It’s hard to put into words what the improvement sounded like. Obviously, the noise problem is solved and actually the noise floor is lower than it has ever been. However, there is more to it. I get the impression that this mic would work well on more voices with the new tube. I’m not sure how. It seams less “peaky” in the upper midrange than before in cardioid mode. When I spoke into the mic, it was as if my ancestry changed. I now felt like I was James Earl Jones, Lawrence Fishburne (see image from Death Wish 2 above) , Morgan Freedman, or some other black dude that white people love.

That was all it took. Changing tubes in the Soundelux U99 was about as complicated as plugging the mic into the power supply.

I’m pumped about trying the new and improved Soundelux U99 on my next session. I have a feeling that my little phase of using my Shure SM7 on as many sources as possible is just about over!

MXL V69 Tube Change
My MXL V69s are having serious problems. While speaking into the capsule does nothing, body noise get’s send through the mic to the preamp. So I figured I’d use my newfound tube confidence and try out new tubes in my V69s. Maybe that would solve the problem.

I need to point out that I own two MXL V69 microphones. Both of them seem to broken in the exact same way even when I try out different mics, power supplies, and cables. This strikes me odd that both mics are having the exact same problems and makes me think that maybe the problem is further down the line (preamp / phantom power) but all my other microphones work fine through the same XLR cable and preamp (Trident S20).

So, just like the Soundelux U99, I unscrew the bottom base and then take off the metal body/housing/pipe thingy. Once gain, there is all the electronic guts. The tube is mounted quite a bit differently in the MXL V69. My immediate response is “hmmm” (as in “this is going to be a real pain in the ass”). Of course, I was mostly right.

I’m always paranoid when I’m working with tubes. Not only does knowledge that tubes have killed people bug me even when I know the mic isn’t plugged into anything, I’m also aware of the fragile nature of tubes. Much like holding a baby, I’m scared I’m going to break it! It turns out that there is this rubber contraption that holds the tube in place. I had to take two screws out the rubber contraption at the bottom of the tube and then kind of tear the tube out of the mic before I could wiggle the tube out of it’s socket. I’d say this took about 10 minutes. I’m sure an experienced person could do it in 1 minute, but I can’t say that I had a screaming amount of confidence about this procedure. The Soundelux U99 was MUCH easier to deal with in this regard.

Eventually I get the new Groove Tubes CV4024 into the MXL V69. I never did get the rubber mount set properly. It was a very awkward procedure at best. It felt like a really crappy way of handling the tube, but I’m sure it was less expensive than the Soundelux U99. What can I expect? I paid 1/8th price for the MXL V69.

So I fire up the V69 and wait about 15 minutes. I’m getting the same exact problem. I hear tones of noise, no signal when I talk into the mic, but plenty of sound from handling the mic. I wait an hour. The results are the same.

Back to the drawing board!

Swapping out the tube in my Soundelux U99 with a Mullard EF86 was DEFINITELY worth the money based on my primitive and very brief initial tests. It solved the problems with excessive noise and such. However, it appears that my problems with my MXL V69 are much deeper than that. I’ll need to explore deeper and pull out my old electronics books first.

Brandon Drury

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Brandon Drury quit counting at 1,200 recorded songs in his busy home recording studio. He is the creator of and is the author of the Killer Home Recording series.

2 responses to Swap Tubes In Your Tube Microphones

  1. I am sorry to hear that you are having trouble with your V69′s.

    You may be interested to know, that we offer outstanding service to our customers, even after warranty has run out. (Incidentally, the V69 has a 3 year warranty)

    Just get in touch, and you will have your V69′s sparkling again in no time.


  2. Thanks Roy!

    I should probably just bite the bullet and send both of my V69s back in. When reliability isn’t an issue, these are some great excellent microphones. I wish there was some kind of upgrade that would make them more reliable.