Looking at Buliding a Stereo MILA

Coming June 9th, the MILA will be have been floating around this forum a year. I would like to order my parts on that day, like a ceremony...

The PSU is what I need a little help on. I would like to use this mains transformer:

New 150VA toroidal transformer. It is precisely made for high-end tube amp or pre amp. It has very low power loss and magnetic leak. Labeled input 115 + 115 Vac (Dual coils), outputs 250Vac x 2 (dual coils) at 250mA each, 6.3V at 3A, and 12.6V at 2A each. This item has CE certified. Mounting hardware is included. The test results are excellent. (note: Please increase 10% of rated power when this transformer use in 60 Hz power source)

Click to expand...

I was thinking I could use a single heater supply and duplicate the B+ circuit on each of the dual secondary. 2 bridge rectifiers, etc...

Would I take both R5(1) and R5(2) to the top of R6?

-or-

Is separate B+ voltage even a necessity here?

Schematic Here

I have the bitchenest chassis for this...

Thanks- BH

Oh wow..... forgot all about this one. I actually built one of these a while ago, and it is actually a very neat mic pre with a sweet top end. I used Nadege's layout and it worked great! Fired up on the first try. Check out some pics, layout and BOM here: http://musiciansgig.com/mila/

I highly recommend building one; it's a really fun project that can be built quickly. Just don't get ZAPPED!!

Take care,

M.

[quote author="madriaanse"] Just don't get ZAPPED!!
[/quote]

Yeah... speaking of which, I turned on a 3 phase 250 amp breaker that blew a hole through the steel door! The system tech had left the allen key in the clamp that ties in the copper and it shorted to ground. Sparks to the ceiling...

Glad to be alive.

OT...

I was also wondering if I could up the 22uf C8 & C9 & PSU C1 & C2 to 32uf to take advantage of the the dual caps available.

Scratch that mains transformer. It wont fit in my chassis.

BH.

If you do build dual plate supplies but a single filament supply, you only need a single R5 and R6 to bias up the filaments; connect them to just one B+ supply.

But...the power transformer you specify is kind of overkill; the high-voltage secondaries are specified at 250mA apiece, and the MILA only draws 10mA per channel. Why not save the super-toroid for something that's more power-hungry and use a less-expensive (and smaller) transformer for the MILA?

Peace,
Paul

[quote author="pstamler"] Why not save the super-toroid for something that's more power-hungry and use a less-expensive (and smaller) transformer for the MILA?
[/quote]

Can you beat $38?

Thanks for the tip!

I don't think any toroids will fit in my chassis, so I'm going to build an external psu as per specification...

What about bumping the caps up to 32uf?

Is anything going to get thrown off?

I like overbuilt things....

BH

[quote author="babyhead"][quote author="pstamler"] Why not save the super-toroid for something that's more power-hungry and use a less-expensive (and smaller) transformer for the MILA?
[/quote]

Can you beat $38? [/quote]

That's a pretty good price, for sure, but check out some of the house-brand transformers from Allied Electronics.

I don't think any toroids will fit in my chassis, so I'm going to build an external psu as per specification...

Click to expand...

A good idea anyway, to avoid hum coupling into the circuit -- yes, even with a toroid.

What about bumping the caps up to 32uf?

Is anything going to get thrown off?

I like overbuilt things....

Click to expand...

Couldn't hurt.

Peace,
Paul

[quote author="pstamler"]
That's a pretty good price, for sure, but check out some of the house-brand transformers from Allied Electronics.
[/quote]

paul's right. i've been searching for a PSU transformer for my dual channel MILA and the Allied Electronics 6K88VG (same one used in my LA-2) is a good match
500VCT @ 40mA and 6.3VAC @ 2A for $19.71 each. better price than the hammond transformers (thought hammond has a little more current capabilities at twice the price, but the Allied is still suitable for the MILA build).
-grant

To get 250v from a 500v CT I just use one of the secondaries and the CT, correct?

I am paranoid of fires...

Thanks- BH

Yes.

Yes

Hi,
I Don't know this preamp, but it seems really intersting.
Who know how it sounds??, could it be compared with a pultec MB1 or tubetech mp1a...I may be stupid to make a comparison....I just want to make me an idea of this preamp :wink:

I hope this ends up sounding like rivers of chocolate!

I plan on using sushi grade cocoa...

Seriously, I'm just trusting NYD.

I can't think of a better thing to with what NYD has given us than to actually build it.

I'm wondering if by doubling the load on the PSU, will I need to make any tweeks?

:guinness: :guinness:

If you are using that 250mA toroid than you don't have to change anything. You can power 25 MILA's HT with it.
For the heaters each tube needs 0,45A at 6,3V or 0,225A at 12,6V. So your toroid could power 6 tubes or 3 MILA's.

Hello,

I hope this ends up sounding like rivers of chocolate!

Click to expand...

goooooood :green:
I think I will try this preamp design
to follow.....

Anything dave drops in design sounds amazing... :thumb: and Dave is one hell of a nice guy... :thumb:

[quote author="babyhead"]To get 250v from a 500v CT I just use one of the secondaries and the CT, correct?

I am paranoid of fires...[/quote]

To use a 500V CT transformer as a source of 250V, there are two ways.

One, as you suggest, is to use one of the hot leads and the center-tap. You'd use that with a full-wave bridge rectifier.

The other way is to use the whole secondary, with the center-tap grounded, and a full-wave center-tapped rectifier. This is the configuration with only two diodes; each hot lead of the transformer connects to the anode (unbanded) end of a diode, while the two cathodes (banded ends) are connected to each other and to the + terminal of the first filter capacitor. The center tap is connected directly to the - terminal of the first filter capacitor.

In either case the DC voltage will be close to 250 x 1.414, less a bit for the diode drops and ripple.

Use at least 1200V diodes.

Peace,
Paul

I have to thank you all for the help with this. This is well on is way because I am now obsessed. This will be the Kunis edition.

I am planning on using 32uf + 32uf JJ multicaps. Before I finalize my layout, I have to ask another question...

Do HV electrolytic caps pose a danger of radiating noise into a tube if it is mounted too close?

I want to mount the dual cap c8 & c9 right next to the tubes and wire all of the tube to cap connections P2P, with liberal shrink...

Does anyone have experience with this?

Thanks yo.

I've seen it happen once in a while. If you want to be safest, and need to mount a cap near a tube, make it the output tube, not the input tube.

Peace,
Paul

Just to put it out there...

I ordered my Cinimag CM-2940 inputs this morning. I am planning on implementing a slightly different input configuration on a 4x3 rotary switch- a 37.5 ohm ct, a 150 ohm, a -20 150 ohm, and a 10k:10k Jensen which is laying around. I wonder if there is a way to do this... maybe not. (if I can find a 4x3x2 mmb switch, I'll do it, otherwise it's 3x4 with a pad on a switch)

I am working on my layout of which I will post seeing as this is my first true P2P project. (half of my G7 is...)

I am also throwing dough at this. Black Gates, tant resistors for the signal, non inductive Vishay and Mills for the rest, copper ground plane, and a bitchin never done before faceplate...

Why not? :guinness:

Good luck on your build.

Please post your findings about your input transformer / rotary switch.

I'm just starting on a 3 ch. MILA build into an old DuKane amp.

Do you have any pics of your PTP G9?