MK47 PCB tube mic kit - build thread

[wave]

Hey wave, cheers for the reply. I'm not sure if he let the tubes burn in to be honest. It didn't seem to be popping for a few weeks when i got it but its getting extremely bad now. I measured the voltage I was getting from the power supply and it was 117 volts. Is this far to high? Would this be causing the pops?

Maybe. Like I said those tubes can def cause some noise and pops and hitting them with 117V might be the cause. There should be a pot in the PSU that you can use to adjust the voltage to 105.
With the mic connected you should try to adjust it.

Dave

 

[burglar]

Thanks Wave.  I think i get it now.  It'll sink in once i read your posts a couple more times. 

You've been a great help.  Thanks again!

B

 

[wave]

Thanks Wave.  I think i get it now.  It'll sink in once i read your posts a couple more times. 

You've been a great help.  Thanks again!

B

No Problem B!
Are you doing a point to point or PCB build for your power supply?

Dave

 

[burglar]

At first i planned to use the PCB but i've decided to do point 2 point.  I was given a load of turrets & G10 + I'll learn more this way.  I just hope that by the time I'm finished the MK47 kits are still available!

The PSU will be my first non-kit project.

 

[wave]

At first i planned to use the PCB but i've decided to do point 2 point.  I was given a load of turrets & G10 + I'll learn more this way.  I just hope that by the time I'm finished the MK47 kits are still available!

The PSU will be my first non-kit project.

Have you had a look at Chunger's build guide for the MK47? He did a P2P and he always has great photos to look at!

Dave

 

[chunger]

Just don't mess up the layout like I did on my 1st go at it  .  I think I have a PDF posted that you can print for my board layout. .. . which isn't the most space efficient, but gets the job done.  I enjoyed building the psu both ways (turret board and Zayance pcb).

I believe ioaudio is committed to keeping the mk47 kits available.  Demand for them comes and goes but I'm sure you will be able to get one when you are ready.

 

[EvLoutonian]

.. I enjoyed building the PSU both ways (turret board and Zayance PCB).

How did you go with your MK47's so far, Chunger?
Did you make a matching pair, or variances in each?
I'd love to hear some audio samples!

Ev.

 

[chunger]

Still waiting for Beesneez capsules to ship so my mic still has the stock (not quite appropriate) Alctron GT-2B capsule.  Looks like a lot of folks got in line ahead of me on this M7 and K7 capsule offer here on the white market   I have been busy lately and not had a chance to build up the 2nd mic, but i have an interesting donor body for mic #2 and should be able to resume building soon.  Audio samples will be forthcoming shortly after build completion, but for now, my timeline is dependent on the capsule backlog at Beesneez.

But, mic #1 is functioning just fine on the temporary capsule.

 

[EvLoutonian]

Oh, great!  I'll look forward to more updates..

I just ordered 10 backup 6028/408a tubes from 'triodeel' on eBay UK, as it sounds like a lot of people are having to cycle through quite a few tubes to get quiet ones.

Seems like a good idea to have some spares up my sleeve, either way.

 

[Majestic12]

Has anybody tried to make the power supply regulated? A simple TL783 could be used to stabilize the B+ on exactly 105V without having to worry about mains voltage drifts.

 

[ioaudio]

The kit was assembled in varying configurations over the last two years.
Some users went with ready-made regulated Psu's (made by Grosser, Drefahl, Hamptone etc.)
Those use adequate circuits to provide for clean well-filtered power.

Depending on your needs the TL783 solution might be too noisy, but one of my costumers went with it and thinks it's perfectly fine.

I once made a tl783 psu and put a lowDCR choke + cap after the regulator to clean up, was fine too.
Another costumer modified a old regulated tube lab supply, nice and heavy.
On the other side i have seen attempts to use finely filtered switched power supplies with modern parts only.

105V @ 0.05A is needed on one or the other way. I still like the original passive Psu most, especially with a split choke like the first original Neumann U47 PSU.
Add a check switch and a voltmeter permanently mounted into the PSU housing if mains voltage drift is a problem.

EvLoutonian,

yes, and do not underestimate the effect of giving the tubes some time to burn in, sometimes it's days before the noise settles.

'chung,

Yes kits will remain on the plate - i still wind and make the transformers by hand, and i rather do that in small batches.
Looking forward to your completed build. I sent you the pcb yesterday.

Waves,

thanks for chiming in!

-max

 

[ioaudio]

A new batch is available at the white market.

 

[laddie.music]

Could anybody point me in the direction for a power transformer for the U47 PSU by zayance???

i'm in the USA therefore his BOM is not relevant for the power transformer for PSU, and i'm not sure which to buy?

I'm guessing the Choke will be compatible either way, the one listed in the BOM?

 

[zayance]

Could anybody point me in the direction for a power transformer for the U47 PSU by zayance???

i'm in the USA therefore his BOM is not relevant for the power transformer for PSU, and i'm not sure which to buy?

I'm guessing the Choke will be compatible either way, the one listed in the BOM?

This one will do: http://fr.mouser.com/ProductDetail/Triad-Magnetics/VPT230-220/?qs=sGAEpiMZZMvwUzoUXIIvyTw34uqMHR%252budKXefz75NmY%3d
the one Chunger seems to use, BUT you won't have a Jewel lamp voltage as seen on other builds.
Beware on the primary and secondary connection, check the pdf of the part, and also the transformer wiring diagram that was sended with the other files, and wire going with the color code marked ON the Toroidal, you never know, they may screw up on a batch, and people will follow pdf :/.

Antek, is another dealer for Toroidal in the US, seems to be out of stock for the ones needed for the PSU, AN-05T200 to be more precise.

And one last thing, i advise you to read through this thread and Chunger's, as this will help you find a lot of things that may help you threw the build, something that i noted on the Safety note pdf that i sended to you also.

Some of your questions points to a lack of searching around and some Electronic knowledge as well (i could be wrong), so i would be more than carefull dealing with my PSU and HT, without reading some things around, and getting a better view of the things to know first before jumping in, my Safety note gives some "notes" about it, but anyway, all is possible, but better be safe than sorry, as always.

Good Luck



T.

 

[wave]

Laddie,
I used the Triad that Zayance listed and you will have to change a few values in the components of the PSU if you go with that trafo.
There is an option for a jewel lamp as Mouser does stock a #47 bayonet lamp that works right off the IEC in. The bulb takes 130VAC so in the US we can use this in our PSUs with a jewel lamp holder (the kind at tube depot).
We have successfully done this over on the DU67 thread. I'll give you the necessary links if you wish to have a jewel lamp.

Dave

 

[laddie.music]

Thanks Zayance, really appreciate it,
i will definately do that,  and yes lack of knowledge on my behalf... i'm good with a solder,  but the PSU will absolutely be built by my friend who is a proper tech.
I will just pass on the parts and information I find through the thread...

 

[braeden]

Received my MK47 kits today, thanks ioaudio!

Also, I know this question has been asked in this thread before but I couldn't really find a definitive answer.

How does one modify the MK47 circuit for a Figure Of 8 pattern instead of the Omnidirectional as standard? (i.e. U47 to U48 conversion)?

I've compared the U47 and U48 schematics but unfortunately my electronics knowledge is lacking at the moment, especially when I am risking a lot of money.

I know there is a difference in the voltage divider resistor values, (3M/3M) as opposed to (3M/2M) as well as the addition of a capacitor from a relay pin, but I'm not sure whether this applies to the 6028.

Could anyone that's actually tried this confirm what modifications are to be done?

Thanks a lot,
Braeden

 

[ioaudio]

Not much harm can be done, just follow the original U48 schematics.
The tube type has nothing to do with the polarisation of the capsule.
Note that the modification provides only 50V polarisation per side.

-max

 

[braeden]

Not much harm can be done, just follow the original U48 schematics.
The tube type has nothing to do with the polarisation of the capsule.
Note that the modification provides only 50V polarisation per side.

-max

Thanks for the reply.

 

[braeden]

Here it is, or isn't for that matter. A 'MK48' schematic.

Any advice is welcome, I don't actually know how correct this is, especially in regards to component values.

Thanks