MK47 PCB tube mic kit - build thread

I've been thinking about your solder issue and maybe the heat is being dissipated down the wire into the coil of the transformer. What wattage/heat are you soldering at generally?

You are wiring it correctly and if you saw the lamp light then it was working. You should def measure it and check the voltage. If you do have 6.3VAC at the secondary, maybe somehow the actual bulb went bad? Do you have any extras?

Just have to figure out why the solder isn't taking. I'm sure you can use some small crimp ends and solder those to the lap housing

Dave

You may need to scrape the clear coating (usually enamel) off the wire with a blade to make a good connection for soldering to on the transformer wires. 

barney said:

You may need to scrape the clear coating (usually enamel) off the wire with a blade to make a good connection for soldering to on the transformer wires.

Click to expand...

Excellent point barney. Didn't think of that myself!

Dave

Thank you!

I scrapped the wires, soldered them to the lamp without any problems. The voltage measures to 7,3 V but the lamp works. That is ok, right?

When I switch between CARD/OMNI, it makes a pop. Is that the way it's suppose to be?

If that is suppose to happen, I'm finished! Thank you all for guiding me towards this build.

And the whole package!

One last stupid question through...

When measuring the PSU voltage I had the multimeter at DC. Was that right?
When Dave said that the sec. 7,3v where AC it got me thinking. Then would the 200v sec. also be AC. And in that case, I don't know why The DIMM could show me the right current in DC mode.

But since I am measuring between 105v and 0. I suppose there's no way that it could be DC. I am a total newbie when it comes to this sorts of electronics.

John

The 6.3V Sec is AC
The 200V Sec is AC
The 105V B+ is DC

If your wall voltage is a little high, that will translate through the transformer and produce higher secondary voltages.
The point of the PSU is to convert the 200VAC to the useable 105VDC.

That small drift you were getting (104.9 - 105.12) could be from drifting wall voltage. Those numbers you were seeing were pretty close to 105 so I wouldn't worry about it.

Dave

Glad you got it working, looking good.  Now I need to get onto finishing mine.

Thanks!

I'm very proud of it. And it sounds amazing.
Yesterday I sat and played guitar in front of it for over 3 hours.
I didn't record anything, just listened meanwhile the tubes burns in. I havn't even heard any crackle, sparks or pops during the burn in.

Good luck with yours.

John

mine is working now too ;D ;D ;D ;D with beez neez capsule and t bone houseing. its veeery quiet.

the mistake i made is really toooooo embrassing to report :

soundwise im in test phase. recorded a violin jesterday - well - i think i miss some highs. perhaps not the best application for that mik. today i made some gitar amp recordings and it seems a nice addition to a direct amp microphone like the shure sms. unfortunatley my female singer was ill so i cant go on this... (thats what i build the mik for)

whats your favored application for the mik?

Well I have just tried it with acoustic guitar and vocals. And it owns every other microphone I got.

But I have been watching how much the voltage are pendling. And it seems to be more than I thought. When DIMM in DC mode it measures from like 103,5-106,3 V.

And if the DIMM is in DC True RMS it's more stable like between 104,8-105,6 V

I measured the the walls AC, and it drifts about 2,9 V so... that explain the drift but can it harm the microphone? Or is that ok?

John

I have seen numerous comments about b+ drifting. I have noticed this drift too over xx number of hours.

I had mine on the bench for several days recently. It was a week if it was a day.

Anyway, I monitored the b+ over several days of continuous use and once I would cal it to 105, it would drift within an hour or two. Came back one morning and it was up to 110. I'm thinking the stock 1k5 sand/power resistor may not be linear wrt heat.

In any case, I see significant drift. Well 5V up or down. That's not too bad in context I guess but a more stable b+ would be nice for consistency.

I see this on 2 mic's.

I may install bananas and a cal-pot to psu chassis to facilitate calibration before / during a session or as needed.

Any other thoughts / observations / comments with drifting b+ ?

BTW, I had one in service on-air 24/7 for a couple weeks under these conditions and it sounded great. I did not monitor b+ during that time though I did receive good feedback from users regarding sound.

Cheers,
JoBu

Couldn't you place a Zener at the end of the b+ voltage rail in the PSU to keep the voltage fairly constant without too much fuss? Then again Zeners drift too...

Probably could but don't those generate noise which we don't want in the heater/cathode ckt (fixed bias)? These things are mostly fine in a cathode/self bias situation though.

Anyway, I'm thinking that the main heater dropping resistor in the mic may be drifting in value as it heats/cools thus changing current draw and Vdrop. I noticed that several people appear to have used the chassis-mount encased style resistors in the 1k5 heater dropper position (attached to the bell) and was hoping that others could test/measure for b+ variance over hours of time or longer...

Mains AC is measured constant 122 in this case.

Cheers,
jb

These mics sound good , nice top end detail with the Bees knees cap .
As soon as I get my M7 holder Ill post a comparison of a dale and a BK

Hey quick q'n how is everyone mounting the pot inside the case? any brakets  Ican buy? or are people making their own?

I made my own. I bought a little aluminum warning tag from the hardware store and drilled it then bent it to hold the pot facing up so I could turn it easily.

Hey everybody! I'm considering building the MK47, but I really want a U47 body for it, and Equinox is out of stock. AMI has bodies, but they use a three-rib system, as opposed to two like the Equinox. Would the MK47 fit anyway? There's also Flea, but it's very expensive, and I have no idea if it's two-rib or three.  Thanks!

hey there,

i wonder the same about the ami body too. Will the mk47 fit? i'm sure it can be made to fit. the ami body is far superior to the equinox.

Big question for the MK47 team

Will the cheaper RK47 from http://microphone-parts.com/rk47-microphone-capsule/ work with this mk47 design????

the reason i ask is cos i'm trying to fit one and there is no bass to the signal. like there a severe high pass filter on the whole time.

Thanks for any thought

Michael

The capsule does work with the design.
Are you sure that your power supply has the cardiod/omni switch in the cardio position?
When I first tested mine my switch was in omni and the mic sounded terrible. I know it's probably not the answer you're looking for but you should try to throw it and see what the other position sounds like. We can then work from there.

Also, what body are you using now?

Dave