MK-U47 - build thread

[ioaudio]

Yes, do not judge the noise behaviour before letting them bake for 48 hours.
The Jan tubes are kind of unique in this regard, but once the noise comes down they'll last very long.

 

[stelin]

Thanks, ioaudio. I will make sure the tubes that came with the kit are burned in before a judge them.
/Stefan

 

[kcatthedog]

I’m now in the process of testing and burning in tubes for my MK-U47. One problem is that there are two tubes in the mic. How do you select the tube with the lowest noise when you have to test them two at a time?
It would be nice to be able to run the mic with only one tube when measuring the noise. But, then the heater will not work, since the heaters are connected in series.
Does anyone have any thoughts or suggestions on that?

I have built two C-12 copies (MataChunger) to. The MK-U47 is about 5dB hotter than the C-12s, but even compensating for that, the MK-U47 is a lot noisier (at least 6db) so far. But then again, I was really surprised how quiet the C-12s with Mullard 12AT7 are.

Does anyone have any experience with the 6028/408a tubes? Do they vary much in noise levels? Do they need a long burn in time?

Thanks!
Stefan

cut to the chase and contact Christian at proaudiotubes, instead of wasting money on questionable tubes why not pay someone a a reasonable price for their professional service and get good tubes that are already burned in, tested and that he will stand behind ?

 

[Category 5]

I’m now in the process of testing and burning in tubes for my MK-U47. One problem is that there are two tubes in the mic. How do you select the tube with the lowest noise when you have to test them two at a time?
It would be nice to be able to run the mic with only one tube when measuring the noise. But, then the heater will not work, since the heaters are connected in series.
Does anyone have any thoughts or suggestions on that?

I have built two C-12 copies (MataChunger) to. The MK-U47 is about 5dB hotter than the C-12s, but even compensating for that, the MK-U47 is a lot noisier (at least 6db) so far. But then again, I was really surprised how quiet the C-12s with Mullard 12AT7 are.

Does anyone have any experience with the 6028/408a tubes? Do they vary much in noise levels? Do they need a long burn in time?

Thanks!
Stefan

cut to the chase and contact Christian at proaudiotubes, instead of wasting money on questionable tubes why not pay someone a a reasonable price for their professional service and get good tubes that are already burned in, tested and that he will stand behind ?

Well, the JAN tubes will likely be fine after the recommended burn in, but for folks who want instant gratification I'll admit Christian is great and it's hard to go wrong with tubes from him.

 

[chunger]

I’m now in the process of testing and burning in tubes for my MK-U47. One problem is that there are two tubes in the mic. How do you select the tube with the lowest noise when you have to test them two at a time?
It would be nice to be able to run the mic with only one tube when measuring the noise. But, then the heater will not work, since the heaters are connected in series.
Does anyone have any thoughts or suggestions on that?

I have built two C-12 copies (MataChunger) to. The MK-U47 is about 5dB hotter than the C-12s, but even compensating for that, the MK-U47 is a lot noisier (at least 6db) so far. But then again, I was really surprised how quiet the C-12s with Mullard 12AT7 are.

Does anyone have any experience with the 6028/408a tubes? Do they vary much in noise levels? Do they need a long burn in time?

Thanks!
Stefan

cut to the chase and contact Christian at proaudiotubes, instead of wasting money on questionable tubes why not pay someone a a reasonable price for their professional service and get good tubes that are already burned in, tested and that he will stand behind ?

Well, the JAN tubes will likely be fine after the recommended burn in, but for folks who want instant gratification I'll admit Christian is great and it's hard to go wrong with tubes from him.

I could be very wrong, but last i checked, Christian does not have a burn-in and test rig for the mk47 tubes.  Otherwise, i would have saved the hassle and purchased a pre-screened tube.

 

[stelin]

That's right,  Chunger. Christian does not have a burn-in and test rig for the mk47 tubes (408a's).  He is selling WE 408a-tubes, but you have to test them and do the burn in youself. I know, because I have two that I bought from him.

When I first put the WE 408's in the mic, they had a bit to much noise. Now, they have been in the mic for 48 hours, and the noise has gone down a lot! The MK-U47 is now almost as quiet as my C-12's, and the noise is also a bit darker, which is a good thing.

 

[stelin]

Shock mount on a shoe string budget... with a shoe string.

I've been waiting for a shock mount from the Land Down Under for some time. Needed a temporary solution.
This is it: A piece of leather from an old guitar strap, four cable ties and a shoe string. The outer ring is from a Blue mic I don't use very often. Not to bad, or what do you think? 

 

[kcatthedog]

Shock mount on a shoe string budget... with a shoe string.

I've been waiting for a shock mount from the Land Down Under for some time. Needed a temporary solution.
This is it: A piece of leather from an old guitar strap, four cable ties and a shoe string. The outer ring is from a Blue mic I don't use very often. Not to bad, or what do you think? 

very good, but chunger at studio 939 has a well priced unit too !

 

[fazeka]

Hi,

As I wait for Matador's/chunger's new PSU PCB and dan's case, I have started building a U87 clone.

But, I read that for that mic, cleaning all flux off is pretty critical due to impedance issues...

However, I didn't do that with my MK-U47 and it is already all assembled (which in and of itself was rather tedious for me). 

Do I have to deflux all my solder connections on the MK-U47? (I didn't see that in the instructions, possibly I missed it?).

 

[Category 5]

Hi,

As I wait for Matador's/chunger's new PSU PCB and dan's case, I have started building a U87 clone.

But, I read that for that mic, cleaning all flux off is pretty critical due to impedance issues...

However, I didn't do that with my MK-U47 and it is already all assembled (which in and of itself was rather tedious for me). 

Do I have to deflux all my solder connections on the MK-U47? (I didn't see that in the instructions, possibly I missed it?).

Since the high impedance parts are floating it shouldn't be an issue.  Max told me this himself.

 

[ioaudio]

Yes,  all the critical HiZ parts are mounted on the acryl desk for this reason, no scrubbing nescessary.
Normal PCB material isn't up to the task - even after scrubbing - in use the pcb will absorb humidity and the resistance will decrease...sometimes only after a while...there is a reason why good mic designers use acryl and/or teflon standoffs for ALL HiZ connections.

-Max

 

[fazeka]

OK, good to know! Thank you!

 

[ioaudio]

Currently the kits are sold out, working on a new batch.

-Max

 

[ioaudio]

11 Kits available now - those are the last kits with the tubes included and probably the last ones for 2014 - get them while they last!
--> http://www.groupdiy.com/index.php?topic=35667.0

 

[kcatthedog]

Testing mike electronics

I set my PSU to 105 V and finished my Gotham cable, but the mike seems to not get power and/or to operate.

On power up Tubes do not glow, I switched in the originals and my 408a's nothing ?

I only have my one new cable with binder  and xlr 7 pin male connectors ,  suggestions for trouble shooting  would be appreciated.

Thanks.

 

[Category 5]

You removed the test load from the psu right Kcat?

Check the wiring of your cable with a meter to make sure you didn't cross wires or get any shorts.  If that looks good it's time to retrace the mic wiring.  If nothing obvious just message me and we will figure it out.  If the tubes don't get hit the heater isn't working.  That's imperitive. 

I'm back in town tomorrow night and can be of better help. 

 

[kcatthedog]

Hey Cat5,

Yes dummy load removed. I have power from pin5 from psu in the mike and have taken readings throughout out the mike confirming power in pin 5 and checking every junctier  to last 2 on cap.  I'll post in a bit.

Pretty certain me bad and I damaged the tube sockets strain testing them during build.

Everything has power and wiring to tube sockets. But no go bet I need to replace the sockets.

Drive safe!

 

[kcatthedog]

After setting rough voltage to 105 V, I disconnected the dummy load and plugged in the mike but I noticed the tubes do not glow or get warm.

I tracked the electricity from the psu 5 pin  from the inside of the 7 pin xlr without the cable attached it is 105v, with the cable attached it is 118V.

so from the bottom of the mike up to the top here are the readings:

Pin 5 in base+ 118v so that confirmed that the cable I made is good

the orange wire leaving the resister is 118v

after the resister the yellow cable is 118V, yellow at the top of the mike socket is also 118V and the second socket also reads 118V

If I check the resister farm, its readings are

Starting at top

this is the end of the wire that sticks through on the far right hand side  Readings on the right and left hand side of the resisters

1 118v   118 117.9
2 106 118 105.8
3 118 117.9 105.7
4 118 117.5 117.7
5 118 117 117.6

At the top of the mike exiting form the yellow yoke my readings are:

Black 117.7
Blue 117.7
Yellow 117.7 1st, 118.3 2nd, 118.2 3rd position (following the wire)
Green 48 1st, 48, 2nd,48 3rd, 48.9 pin top of mike, 49 at mike
white 105.6 , 117.5 pin to mike, 117.5 last pin


Green to right of reed switch 48.9
Yellow left of reed switch       44.4, pin to mike 44.1

I took readings by keeping my black probe to the ground at the switch in the psu and probed with the red following the circuit by wire colour code bottom to top.

The tubes never lit up nor got warm during this process.

So, there appears to be electricity everywhere it is supposed to but the tubes get now power?  I think I damaged the sockets and need to replace them.

 

[Category 5]

You want that 118 to be 105 with the mic connected. 

From memory yellow is heater and should read about 20V. Red should be 105.  Blue is the output so you shouldn't see those volts there.  Double check the tube wiring and make sure it's the same as max's revised drawing.  Also double check the connections at the pcb and make sure there are no shorts and the connections are correct. 

I doubt you killed the tube sockets.  They are pretty simple and robust. 

 

[ioaudio]

Kcat,

sorry for the delayed reply. At this point i must warn you to be very careful with the voltages involved in such a tube project!
Please refrain from powering up the mic in this condiction. You will haver to check all connections again before the next power up attempt.
Do you have anyone nearby who could help you in person?
If not, you might consider sending the mic back top me for a checkup.

-Max