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Success Stories If you have successfully repaired or restored a piece of equipment, why not write up what you did and post details here. Particularly if it was interesting, unusual or challenging. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

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Old 22nd Jun 2021, 11:38 pm   #1
Uncle Bulgaria
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Default Metal Bashing: Uher Miniline 220V Bucking Box

Our mains is quite high (at present 247V) and I noticed my Uher Miniline stack, marked 220V, was getting very hot in use.

The advice from Members here coalesced around a bucking transformer. After reading up on the Elliot Sound Products page on these, I wired a Velleman 209009C dual 9V transformer in ESP's recommended autotransformer configuration. It wasn't going to fit in the tight casings of the Miniline stack, so I took advantage of the relaxed Covid restrictions to get access to a workshop and some metal bashing advice from my brother, planning to make a case that matched the Uher aesthetic.

After calculating and drawing the folded net on a piece of filing cabinet panel, I snipped with shears and a Monodex nibbler, before filing to the scribed lines.

Lockdown has taught me basic welding, and I've made a bender to help put new sills on my car. This box was its first test. While a bit indelicate, I eventually got the folds in the right place, with only some areas that required soldering and filing back.
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Old 22nd Jun 2021, 11:47 pm   #2
Uncle Bulgaria
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Default Re: Metal Bashing: Uher Miniline 220V Bucking Box

The top was a single piece bent to form three sides, with similar small screws used to hold it down as on the rest of the Uher stack.

A few coats of high-build primer, and Halfords Satin Black made quite a good match.

The electrical innards are simple - an IEC plug; the neon bulb and clip-in orange shade from a broken shower pull-switch; the transformer and a Cannon LNE mains outlet, where the Uher Z140 power amplifier is connected. I used these because I happened to have some, they were unusual enough not to be used on anything else I'd ever seen, and they are around the same period as the stack.

For my further amusement, I am planning to make some decals or screen-print similar legends on the top to make it appear more like a genuine artefact.
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Old 22nd Jun 2021, 11:49 pm   #3
Uncle Bulgaria
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Default Re: Metal Bashing: Uher Miniline 220V Bucking Box

Pictures in situ.

I'm quite pleased with this, as my first foray into metal-bending. I need to get better at not expecting a first try to be spot on, especially with rudimentary tools and no experience. The paint covers a multitude of sins, and the perfect is the enemy of the good.
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Old 23rd Jun 2021, 12:19 am   #4
Cruisin Marine
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Default Re: Metal Bashing: Uher Miniline 220V Bucking Box

That is a fabbo end product- well done mate!
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Old 23rd Jun 2021, 5:08 am   #5
Radio Wrangler
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Default Re: Metal Bashing: Uher Miniline 220V Bucking Box

I might have missed seeing it, but is there a fuse?

David
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Old 23rd Jun 2021, 7:43 am   #6
DMcMahon
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Default Re: Metal Bashing: Uher Miniline 220V Bucking Box

Excellent and professional job, well done Uncle Bulgaria, has it cured the hot running issue ?

David
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Old 23rd Jun 2021, 10:59 am   #7
Uncle Bulgaria
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Default Re: Metal Bashing: Uher Miniline 220V Bucking Box

Thank you for the kind comments! It is nice to show and tell to people who aren't your family.

I haven't tested it for more than a few minutes yet - I need to hook up the 'speakers and demote the Ferrograph from record duty for a little while. Luckily there's a Bandcamp order on the way...or the World Test Final's looking interesting...

Quote:
Originally Posted by Radio Wrangler View Post
I might have missed seeing it, but is there a fuse?

David
Not in the box, David. I considered it, then thought it was unnecessary. There's a suitably sized fuse in the plug, and another where the cable enters the Z140 power amplifier.

The Z140, and by extension the stack, are isolated from mains earth. The original mains cable, which now terminates in the Cannon socket, is two-core. As the new bucking box is metal, I've tied it to the safety earth from the IEC with a star washer and ring terminal under the transformer attachment point, thinking that was sufficient for the fault conditions I could foresee.

If more august Members think it advisable, there is room inside the box for an in-line fuse - I'm loath to drill the case again for a panel-mount one!
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Old 23rd Jun 2021, 11:49 am   #8
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Default Re: Metal Bashing: Uher Miniline 220V Bucking Box

I was just thinking in case it got re-purposed, used for other things or went out of your hands. 13A plugs are notorious for people shoving any fuse they can find inside. I understand the entire rock music industry was founded on the perfect fit of a 1/4 inch jack plug barrel section into the fuse clips of a plug....

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Old 23rd Jun 2021, 4:20 pm   #9
John Caswell
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Default Re: Metal Bashing: Uher Miniline 220V Bucking Box

I have to admit being a bit unhappy about the Cannon power line connector as it is non approved.

John
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Old 23rd Jun 2021, 6:05 pm   #10
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Default Re: Metal Bashing: Uher Miniline 220V Bucking Box

Quote:
Originally Posted by Radio Wrangler View Post
I might have missed seeing it, but is there a fuse?
If one is fitted then there is an interesting question concerning where it should go and what rating it should be. Personally I'd fit a fuse in the incoming mains wiring, suitably rated to protect the bucking transformer secondary from an over-current fault.

This might well not disconnect the transformer primary, though, in the event of a fault within it (the primary). A lower-rated fuse could be added, just in series with the primary, to give that protection. But then the consequences of that fuse opening would have to be considered. Now the secondary would essentially become an inductor, perhaps with a reactance high enough that a lot more than 10VAC appears across it. Transformer action would result in a very high voltage appearing across the primary. What harm might that do ? Is the small primary fuse actually likely to do more harm than good ?

I'm not sure there's a simple solution to this problem with the bucking transformer scheme. I've just realised though that any discussion of it might not really belong in a thread about metal-bashing ...

Cheers,

GJ
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Old 23rd Jun 2021, 7:13 pm   #11
barrymagrec
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Default Re: Metal Bashing: Uher Miniline 220V Bucking Box

Quote:
Originally Posted by John Caswell View Post
I have to admit being a bit unhappy about the Cannon power line connector as it is non approved.

John
It is non approved now but many thousands were in use at the BBC with surprisingly few deaths.

It appears to be used the non standard way round here though.
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Old 23rd Jun 2021, 7:40 pm   #12
merlinmaxwell
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Default Re: Metal Bashing: Uher Miniline 220V Bucking Box

Quote:
It appears to be used the non standard way round here though.
Rated both ways in the day. A rather nice connector IMHO.
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Old 24th Jun 2021, 11:09 am   #13
Uncle Bulgaria
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Default Re: Metal Bashing: Uher Miniline 220V Bucking Box

Quote:
Originally Posted by John Caswell View Post
I have to admit...
Thanks for the comment, John. The connector is solidly built and originally rated for mains, and its 1970s-ness was part of the reason I chose it. Its locking mechanism is ergonomically pleasing and secure. Certainly easier to use than an IEC! In this case it's passing less than an amp, so I don't think it's a weak link.

Quote:
Originally Posted by GrimJosef View Post
If [a fuse] is fitted then there is an interesting question concerning where it should go and what rating it should be...
This is beyond my ability to deduce before the fact, so your analysis is very informative. As far as I can tell, the current fusing system protects the important parts - the wire from fire and the Uher stack from repair.

Radio Wrangler's point about a subsequent user had crossed my mind, but as it's unlikely to leave my hands for the next half-century I am not very worried. Besides, the case will have labelling detailing the fuse requirements, just like a Uher Z131 cassette power supply. Then if the value's wrong (as it was in the Z131 I have here) at least it's obvious.
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