MK47 PCB tube mic kit - build thread

[lonepariah]

Thanks for the advice Don, I will check there. I really hope there is enough interest.

Chris

 

[soundcollage]

What is the importance of the extra leads going to the glass tubes? Why not mount the front directly to the grid socket pin and the rear directly to the relay pin? The only thing I can think of is to prevent possible proximity problems if the flexible wires move close to another component during assembly, and if that's the case would it not be better to put the glass insulators in the top mounting plate and run stiff bus wire from the grid pin and relay up through them and solder the (shortened if necessary) capsule leads to them there?

 

[Jonkan]

Ok quick question. Im testing my Psu and with no mic connected, test switch on (2k3 load), im getting either 105v or 0v on the pattern selector. This isnt correct right? Why is there no voltage drop over the 14k resistor?

Or should i connect the mic and test this again?

/J

 

[bobine]

Ok quick question. Im testing my Psu and with no mic connected, test switch on (2k3 load), im getting either 105v or 0v on the pattern selector. This isnt correct right?

Or should i connect the mic and test this again?

/J

According to the schematic, you should have 48v or 0v at the pattern selector. So don't attach the mic until you fix it!
Do you have the 14K resistor before the pattern switch?  Check the schematic: In the off position, you will have 14K plus 12K resistance to simulate the relay load.

 

[Jonkan]

Ah, stupid me. I measured in the incorrect place! I measured at the pattern supply, but theres no relay load there when mic isnt connected. When i measure after the 14k resistor, i get 48v!

That seems much better!

/J

 

[toffifee]

What is the importance of the extra leads going to the glass tubes? Why not mount the front directly to the grid socket pin and the rear directly to the relay pin?

Exactly what I thought and then did - works!

 

[Peps]

Hi Max (and everybody else),

I have assembled a MK47 (with a Sigfried Thiersch PVC capsule) and it sounds fine and behaves exemplary. But I can't help worrying about the PSU. The HT keeps wandering slowly between 104.5 V and 105.5 V in an approximately one minute cycle. I use two chokes in series (see attached picture) - could that be the cause of this phenomena? Would it be better to have the second filter capacitor connected between the chokes ( more in line with the original U47 PSU, I think)?
Could the physical aligment of the chokes have an influence (magnetic coupling)? I have them lined up one after the other with about two centimeters in between. Whaddayathink?
I would appreciate any ideas!

Thanks
Peps

 

[mad.ax]

First thing to check would be your AC wall voltage. Does it keeps wandering slowly between 229 and 231V by chance?

Axel

 

[Denyle Guitars]

Mine drifts by more than 1 volt, so you're doing pretty well to keep it b/t 104.5 and 105.5. What I did was set my DMM range to 750v so I don't see it drift.  ;D

 

[soundcollage]

Would it not be more effective with a cap to ground between the chokes? Though, I doubt that has anything to do with the drift.

 

[Peps]

First thing to check would be your AC wall voltage. Does it keeps wandering slowly between 229 and 231V by chance?

Axel

Axel, you were absolutely right! I feel a bit stupid - it is a unregulated supply after all ... 8)

Would it not be more effective with a cap to ground between the chokes? Though, I doubt that has anything to do with the drift.

That's what I meant when I said "capacitor between the chokes". I guess I should try that.

Thanks for the support!
Peps

 

[gec]

I'm to order a Thiersch Blue capsule for my microphone, I'm using a T-Bone Sct700 body.
Is the STW 7 (blue line) capsule with the "STS 7 c (52mm)" holder the right combination for the body?
Thanks...

 

[kante1603]

I'm to order a Thiersch Blue capsule for my microphone, I'm using a T-Bone Sct700 body.
Is the STW 7 (blue line) capsule with the "STS 7 c (52mm)" holder the right combination for the body?
Thanks...

Hi,

I did the same except of the capsule (red line),but it´s identical in mechanics.Most important thing is to take the "C"-Type of the STS7.The others will bring the capsule too close to the top.Looking through the basket against some light shows that the position is nearly exactly the same as it was in the original!

So-YES!-perfect choice!

Have fun with this awesome microphone,

Udo

 

[bobine]

I'm curious to try a Thiersch capsule for my second MK47.  Has anyone compared one to the Beezneez K7 from the group buy?  Compared red line to blue line?

On the other hand, the Beezneez capsule sounds so incredibly good, I would't want to be disappointed! Mainly I'm curious to learn how these things sound.

btw...I fired up the 2nd MK47 last night and it sounds and behaves exactly like the first one. Success!

 

[soundcollage]

I figured that's what you meant Peps, I was just hoping someone else would weigh in on the subject as I'm about to start construction on my power supply.

 

[monkey]

Got my MK47 up and working, with a Thiersch red line capsule and Equinox body. I've burned in the tubes and it is mostly quiet and basically sounds okay.

I notice that it's a little pointy sounding in the high mids and there's some slight distortion, which is mostly noticeable on sustained notes. The brightness almost sounds like it could be harmonics generated by the distortion vs a shaped response, and there's plenty of lows. Since this is generally considered a darker circuit, and is known for smooth mids, I'm assuming this isn't quite right? (It's been a few years since I've used a real U47, but I remember it being anything but peaky sounding.) I know the Thiersch blue line is supposed to have smoother highs, but the red should still be on the smooth side compared to most mics.

Here are my readings:

Supply: 105V
Heater : 38.1V (Between heater and dropping resistor)
Cathode: 1.22V (Between 27R resistor and pin 2/7)
Plate(?): 43.5V (at the jumper)
Capsule: 56.6V (At the voltage divider)
Output cap: 43.3V

These seem in the ballpark. Thoughts?

@Bobine... did you ever track down the source of your mysterious 4/8k spike? I wonder if this something similar.

 

[bobine]

@Bobine... did you ever track down the source of your mysterious 4/8k spike? I wonder if this something similar.

I think my spikes are coming from my AC supply or distribution or the PS. I get them even with the mic disconnected from the cable (but only if the cable is attached to the PS). Happens with both power supplies.

 

[monkey]

If you keep dividing 8165(hz) by 2, you eventually get to 63.7. Harmonics of AC unfiltered source noise? (I know nothing about these things).

 

[Le Roux]

Finished mine with a Blue line Thiersch capsule.
Burned in tubes for 24 hrs until no pops

Had lots of room noise, maybe a slight hum and lacking low end.
(I tried the capacitor instead of capsule and ruled out power supply)

Changed up for a Dale M7, which sounded thin, and far away. Cracked and popped alot.

Went back to the Thiersch, and it lost all jam. I mean, I have to turn my pre-amp up almost all the way just to hear it.

Recordings are horrible, very thin, however there is no room noise of hum.

Tried resoldering capsule wires with no luck

When I first tried the mic, it sounded good, and its just been getting worse.

Any idea's?
Thanks

Also, should I be able to measure 60V across front capsule to rear? Or front to backplate?
I am only able to measure around 7V

 

[monkey]

Check your voltages. Search the thread for where to measure and what they should be.

How have wired your ground? With missing low end, I'd also look at the transformer connections.

Good luck!