#1
Hi All,

One main concern here: I've been designing a tube pre-amp with the aim of powering a 12BH7 off the mains (I'm in the UK). I know about bridge rectifiers and all that jazz but with regards to the transformer, what should my main concerns be regarding EMC regulations or any other standards with regards to designing.

This is the transformer I'm using:
http://www.musikding.de/Toroidal-transformer-230V-185V-63V

It has the CE mark...

Is this isolated?
What about reverse inrush current?

Cheers
Guitars & Gear:
Parker Nitefly M
Sumer Metal Driver
Ibanez RGD2120Z
AMT SS-11B
Two Notes Torpedo CAB
Last edited by Emperor's Child at Jan 30, 2014,
#2
The use of a transformer means that it is isolated. You'll want to make sure that any exposed metal is connected back to ground connection on your power cord. This should be a single high gauge wire either soldered or bolted well onto the chassis.

Make sure you wire the fuse into the hot side of the AC line. This is helpful in making sure that you don't end up with an amp that has high voltages. Also wire the far end of the fuse holder as the inlet that way you can't get shocked removing the fuse. Switches should either be on the hot side, or break both sides.

Are you designing to manufacture for sale, or just for your own use? If its for personal use you can do just about anything.
#3
is it just one 12bh7? that transformer only pushes out 40mA off the HT and 1.4A odd the heater supply. if its just one tube, then I think you should be ok, if is more youd be pushing it. that transformer also doesnt have a datasheet/diagram to look at.

cant really see if its 185-0-185, 185-185, 92-0-92, 92-92, 6.3-0, 3.12-3.12, etc.
Marty Friedman is GOD!

curently in a SEX MACHINEGUNS and X JAPAN phase AND Galneryus AND Anthem phase

damn J-Metal, why you so awesome

My Gear:

Schecter Hellraiser V-1 fr
Ibanez RG321mh
Fender GDC-200sce
Peavey Vypyr 30 w/ sanpera 1
#4
Yes, I've already read about making sure I fuse and switch the live wire. I've ordered a kettle socket with a built in fuse tray so that should be fine.

With regards to the ground connection, am I right in thinking that the ground wire from the mains needs to be bolted to the chassis and any earth points in the circuit:
http://www.richieburnett.co.uk/dcsup01.gif
(i.e. in this diagram the -ve rail would be connected to the earth from the mains/chassis)?

It's for my Elec Engineering Degree so although I have no plans to sell, I would like to consider regulations and such.
Quote by bustapr
is it just one 12bh7? that transformer only pushes out 40mA off the HT and 1.4A odd the heater supply. if its just one tube, then I think you should be ok, if is more youd be pushing it. that transformer also doesnt have a datasheet/diagram to look at.

cant really see if its 185-0-185, 185-185, 92-0-92, 92-92, 6.3-0, 3.12-3.12, etc.
It's one 12bh7 and a couple of power mosfets. I've got a mini diagram on the transformer itself: it's a 230v AC on the primary going to a 6.3v AC secondary and a 185v AC secondary so no centre taps.
Guitars & Gear:
Parker Nitefly M
Sumer Metal Driver
Ibanez RGD2120Z
AMT SS-11B
Two Notes Torpedo CAB
Last edited by Emperor's Child at Jan 30, 2014,
#5



the ground connection should be from the ground pronge to the chassis next to the socket.

the circuit ground can be anywhere else on the chassis.
Marty Friedman is GOD!

curently in a SEX MACHINEGUNS and X JAPAN phase AND Galneryus AND Anthem phase

damn J-Metal, why you so awesome

My Gear:

Schecter Hellraiser V-1 fr
Ibanez RG321mh
Fender GDC-200sce
Peavey Vypyr 30 w/ sanpera 1
#6
For the UK your wiring code at the AC inlet should be

Line - Brown
Neutral - Blue
Ground - Green and Yellow striped.

There isn't much you can do in terms of EMC/EMI for a guitar amp. You could always put an AC inlet filter, but since your design only uses 1 tube you probably won't see many benefits.

Other things you can look into, MOV after the fuse across line and neutral. This is basically a surge protection device as it will short in an over-voltage condition and cause the fuse to blow. I actually use an MOV in almost every amp I build now.
#7
Ok, sounds good guys. I might look into adding a varistor to the circuit. Even as an afterthought, it shouldn't be too hard to implement.
Guitars & Gear:
Parker Nitefly M
Sumer Metal Driver
Ibanez RGD2120Z
AMT SS-11B
Two Notes Torpedo CAB
#8
I'm not a big fan of MOVs. They have a crummy failure mode and suffer from other disadvantages. I see them used in a lot of designs and have replaced a bunch of them. Wish I had a dollar for every MOV I've replaced.