Cheap PSU mod to power an U47 clone ?

[innercityman]

Hi everyone,

I'll start to build an MK47 from Ioaudio bought on the black marcket and I'm actually searching for parts... Mic body, capsule, PSU case etc... I found this cheap Tube mic PSU on eBay... Do you think it could be a good choice to power the MK47, and could it be easily modified or will I have to almost start from scratch ?

Here's the link of the PSU

https://www.ebay.fr/itm/DELUXE-VINTAGE-SYLYE-TUBE-VALVE-7-PIN-MICROPHONE-POWER-SUPPLY-UNIT/352960018975?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908105057%26meid%3D27f5008437d24a2cb7999be087e90d8f%26pid%3D100675%26rk%3D4%26rkt%3D15%26mehot%3Dnone%26sd%3D362889269743%26itm%3D352960018975%26pmt%3D0%26noa%3D1%26pg%3D2380057&_trksid=p2380057.c100675.m4236&_trkparms=pageci%3A0aedb770-8eb4-11ea-b6fd-74dbd1802d38%7Cparentrq%3Ae43291d51710ac3dcde71cdcffba49e2%7Ciid%3A1

and here's the schematic....

 

[Khron]

I definitely wouldn't call >100gbp "cheap", especially for a VERY low-power power supply.

How about this, though? Likely much the same thing, but half the price (even if you include shipping):

https://www.thomann.de/gb/the_tbone_psu_sct_2000.htm (Thank RuudNL for the tip ;D )

 

[wlinart]

And if you like the other look more, here is the same psu for about half the price: https://www.thomann.de/gb/the_tbone_psu_retro_tube_ii.htm

 

[mhelin]

And if you like the other look more, here is the same psu for about half the price: https://www.thomann.de/gb/the_tbone_psu_retro_tube_ii.htm

I've got one, it's wiring and the wire is very low quality. If you touch the wires inside when like modding the circuit the wires may broke. They have become so oxidated I guess.

 

[wlinart]

I have two of them running here, and don't have any problems with it. I guess it's the same old China Quality Control? Some good experiences, some worse.

 

[innercityman]

Ok, thanks for the links.

But would it be able to power an MK47 mic from IOaudio without too much modifications ?

 

[wlinart]

The MK47 microphone requires 105VDC for both the B+ and the heater. This psu gives about 200V for the B+ and 6.3V for the heater. So i don't think it can be easily modified. Probably the amperage of the transformer for the B+ isn't high enough, and you can't make the 6.3V up to 105V.

 

[innercityman]

I've read on the MK47 help thread that it requires both 105V and 6,3V secondary, and here's the power transformer that it needs. Info taken on the BOM list. If there's a trimmer inside the PSU, I thought I could trim it to get the 105V required. But anyway, if it doesn't match, I will empty it and replace everything, just keeping the case, sockets, switch, light...

https://www.tube-town.net/ttstore/toroidal-30va-8808.html

 

[RuudNL]

The filament current will be something like 300 mA.
No problem, because the 12AX7 (ECC83) used in most Chinese microphones draws the same current.
Then the +HT. How much current do you want?
1 mA? Also no problem!
If you want 105 V, you will have to change the two zener diodes.
I use 120 V for my microphones and besides that: how critical is the +HT?
(Maybe you should only check the polarisation voltage for the capsule.)
Never had a problem with these 'cheap' power supplies...

 

[Gus]

The MK47 microphone requires 105VDC for both the B+ and the heater. This psu gives about 200V for the B+ and 6.3V for the heater. So i don't think it can be easily modified. Probably the amperage of the transformer for the B+ isn't high enough, and you can't make the 6.3V up to 105V.

The above is good information

Two 20V  heaters in series instead of the VF14 heater using the same type of circuit as the u47
Heaters are rated at 50mA and I would guess the MK47 has them underheated so maybe they are not run at 50mA but something lower.
https://frank.pocnet.net/sheets/185/6/6028.pdf
a thread from 2019
https://groupdiy.com/index.php?topic=50694.680

 

[RuudNL]

If you want to use the +HT also for the filament, the 'cheap' will not deliver enough current.
But... if you use the +105 V for everything, there will be a lot of energy wasted in the  resistor in series with the filament.
That is why these microphones will get so HOT!
Personally I would prefer separate power sources for the filament and the anode voltage. (Depending on the tube.)

As far as I know, using a single voltage for both the heater and the anode voltage has never been done after the U47.

 

[innercityman]

Personally I would prefer separate power sources for the filament and the anode voltage. (Depending on the tube.)

The MK47 uses two 6028 tubes

 

[RuudNL]

I have built an MK47 with two 6028 tubes for a friend. (There are several 47 clones, with different tubes.)
Personally, I wasn't impressed by the self noise of the microphone.
And it ran VERY hot. (As my friend said: "you can fry an egg on it!"...)