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Post by deehope on Jul 29, 2020 16:35:57 GMT -6
   I picked up one of these tube mics a few months ago and was planning to sell it. Long story short i'm stuck with it but I got it for almost pennies and surprisingly it doesn't sound that bad. Its supposibly the alctron mk47 microphone rebadged, not sure if that's also similar to the wa47 circuit. I can upload some pics if you guys would like. Its got a k67 type capsule in it. First mod I'm thinking of doing is a k47 capsule. I missed out on a heiserman k47 for under $200. Im leaning towards the ak47 from advanced audio as well as his 6.5:1 transformer. Tube wise im choosing between a GE5751 and a Mullard Military Issue 12AT7 from Christian. Any suggestions? I always hear about PIO capacitors in these vintage mics. Would that make any difference in here? Can't wait to hear your suggestions... I'm looking to go all out and experiment on this thing. |
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Post by svart on Jul 30, 2020 8:55:04 GMT -6
I picked up one of these tube mics a few months ago and was planning to sell it. Long story short i'm stuck with it but I got it for almost pennies and surprisingly it doesn't sound that bad. Its supposibly the alctron mk47 microphone rebadged, not sure if that's also similar to the wa47 circuit. I can upload some pics if you guys would like. Its got a k67 type capsule in it. First mod I'm thinking of doing is a k47 capsule. I missed out on a heiserman k47 for under $200. Im leaning towards the ak47 from advanced audio as well as his 6.5:1 transformer. Tube wise im choosing between a GE5751 and a Mullard Military Issue 12AT7 from Christian. Any suggestions? I always hear about PIO capacitors in these vintage mics. Would that make any difference in here? Can't wait to hear your suggestions... I'm looking to go all out and experiment on this thing. Just reading up on the Alctron MK47 it seems that it's more similar to the Apex460 and the C12-like circuit that uses and has nothing in common with a U47 besides a body that looks similar. Having modified multiple Apex 460's into C12's and 251's and built my own U47, I can offer some ideas. For the U47 I went with NOS russian polystyrene caps and NOS russian PIO caps. I did not try anything else since these were closest to the vintage stuff that would have been in the original U47. The styrenes worked fine in high impedance coupling and the PIO worked well in the output coupling to the transformer. Ebay is your friend for NOS vintage caps like this. For the C12/251 clones, I just used whatever I had, so normal polypro caps for the most part. The big trick with the Apex460 is that the transformer is mis-dampened with filtering caps that shouldn't be used and it causes the transformer to ring wildly. Without the caps, the transformer is actually really quite good. I also changed to edge-terminated C12 capsules from somewhere I can't remember. I bought a couple and chose the best sides for the primary side of the mic. This has good info for some of the apex 460 mods: www.foxaudioresearch.ca/The460secret.htm |
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Post by deehope on Jul 30, 2020 17:46:47 GMT -6
thanks as always Svart. I was looking forward to your post. I uploaded some pics as Im really not sure if its the aphex 460 or a circuit similar to the u47. Do you need me to take the mic completely apart or are these good enough?
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Post by svart on Jul 31, 2020 6:29:37 GMT -6
thanks as always Svart. I was looking forward to your post. I uploaded some pics as Im really not sure if its the aphex 460 or a circuit similar to the u47. Do you need me to take the mic completely apart or are these good enough? It's definitely like the 460. Same number of resistors and caps. It's hard to trace through pics since they used a single black PCB this time instead of two single-sided green ones. |
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Post by Deleted on Jul 31, 2020 8:30:32 GMT -6
An AKG CK-12 should be available for under 250 USD (new).
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Post by Deleted on Jul 31, 2020 8:50:04 GMT -6
I googled a bit and found Zenpro selling one for 230. Also Tim Campbell makes (still?) a replika of the brass CK12, which many like, for ~400 USD (depending on exchange course to danish crown). www.timcampbell.dk/ |
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Post by deehope on Jul 31, 2020 9:14:57 GMT -6
thanks Guys. so i can go more in the 251/c12 direction? (which I actually prefer). I had a warm 251 here before. So all the upgrades I was researching on the warm 251 would be applicable here? thanks again.
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Post by Guitar on Jul 31, 2020 9:32:06 GMT -6
I haven't done a 47 style yet, so I can't really comment on those.
For the K67 mic, get a decent capsule, and run a 1,000 pF cap from tube anode (plate) to ground, to flatten the top end. This is a secret I got from Fox Audio Research, works really well. It works roughly the same as the neumann "de emphasis" circuit but is much simpler.
My 251 style mic that is my main vocal mic, I use an ADK GK-12d capsule, with a 330 pF polystyrene cap from tube anode to ground, to just take the edge off the top. This is my "secret" value after a ton of experimentation. This is not a "beefy" sounding capsule it's more tight and focused. If you want that big low end you're probably going to want to look at the ADK GK-251d or a 47 style build.
I would avoid the Peluso CK-12 style capsules, they are too bright for me. I couldn't really get them dialed in.
Beezneez and Tim Campbell are my fantasy capsules to try, I just haven't bought any yet.
The big coupling cap I really do like paper in oils if you can fit them. For the 251 mic I used a Sprague TE-1501, to tame it a bit. You could probably use any reputable electrolytic capacitor, or a wet tantalum (original vintage mics used these, very expensive component).
Pay attention to every god damned component in the mic, you can hear most of them. For example the grid bypass capacitor can't be a cheap nichicon, it has to be something nice like a Silmic II. You'll hear it in the upper midrange.
The capsule coupling cap is important as well. Polystyrene works fine. Or you can use one of those yellow guitar amp style film caps, I don't remember the brand.
Tube matters. Get a cheap low noise one for testing, then find a deal on an NOS tube to "upgrade" for your keeper mic when you finish the build.
You're probably going to have to lower the voltages coming from the power supply also, there is a super long thread on this on some forum called HomeRecording or something, the main person to look at is called Lucio I think. He has a .pdf file about the mods I believe.
I posted some preliminary/prototype schematics on there too, that eventually got reworked in my final mics.
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I picked up one of these tube mics a few months ago and was planning to sell it. Long story short i'm stuck with it but I got it for almost pennies and surprisingly it doesn't sound that bad. Its supposibly the alctron mk47 microphone rebadged, not sure if that's also similar to the wa47 circuit. I can upload some pics if you guys would like. 
