Post by Owen Y on Jan 10, 2020 10:06:36 GMT 12
Further to the discussion thread on Field Coil Loudspeakers... I'd like to rebuild the PSU for Field Coils (below), which were previously rather 'thrown together' IMO... Also, sitting on the floor near the lspkrs, I'd like them to be a bit taller, for practical reasons - more visible & to avoid tripping over them! 
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Post by Owen Y on Jan 10, 2020 10:16:43 GMT 12
Rough concept of the rebuild / reconfigure: 
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Post by Owen Y on Mar 6, 2020 20:23:10 GMT 12
Owen, did you go any further with the valve rectified power supply? Hi colinf - I've been struggling for time but yes, I am rebuilding the PSUs into more elegant chasses. They sit on the floor, so also a smaller footprint & taller form factor for easier on/off switching. Something like this:  
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Post by Owen Y on Mar 6, 2020 20:32:29 GMT 12
The volt-meters have arrived from AliExpress - NZ$11.77 ea incl shipping. Plastic cased, not as nice of course as the vintage Westinghouse 'bakelite' meters I have a few of, but we'll see later if they're adequately accurate. They're big enough though (90mm diam) to be easily readable. 
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Post by colinf on Mar 7, 2020 19:36:44 GMT 12
Love the hand drawn pictures, it looks like it is competing in a targa rally stage! Surprisingly low cost for big meters like that. Regarding the orientation of the two transformers above each other, you don’t want both cores in the same magnetic plane as the choke will pick up the stray magnetism of the power transformer. Rotate the choke by 90 deg. vertically.
AMR-iFi R&D
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Post by Owen Y on Mar 8, 2020 14:11:49 GMT 12
TX/coil orientation - I usually orientate coils/core, rotated 90deg on the vert axis... do you you think that I should rotate also the choke say, also around its horiz axis? eg. like this?....
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Post by colinf on Mar 8, 2020 20:16:43 GMT 12
The video illustrates it well, it would be great to use your cro to orientate the choke for least hum as that’s even more accurate that just plonking it there and hoping for the best!
AMR-iFi R&D
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Post by Owen Y on Mar 8, 2020 22:27:13 GMT 12
I should do this in all my amplifiers!
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Post by Owen Y on Apr 21, 2020 20:51:24 GMT 12
Some progress with proper scale check-layout. PTX & choke oriented as per above Youtube advice! This will be a quick build (I hope), as it is a digression from (re)installing the drivers themselves. Also, time is at a premium presently, with 4 adults & a baby in our domestic 'bubble'  The narrow form factor arose from (a) getting 2 front panels out of 1 x A4 sheet of perforated metal that we have here & (b) keeping the floor footprint compact. 
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Post by sadface on Apr 23, 2020 15:55:06 GMT 12
Cool,
I look forward to seing what these come out like.
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Post by Owen Y on May 1, 2020 13:03:05 GMT 12
Interior 'frames' cut from scrap plywood.  The whole box is built around these narrow front plates, which were cut from a single A4 piece of perforated 1.0mm aluminium that we happened to have. 70 diam. holes for the volt-meters.  A quick spray with s. gloss black enamel, to match the meters (together with wood-screws). 
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Post by Owen Y on May 8, 2020 16:11:40 GMT 12
The back plates cut from some old embossed aluminium sheet (LHS) & sprayed same enamel semi-gloss black. With a hole for the mains cable. 
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Post by Owen Y on May 8, 2020 16:17:24 GMT 12
Slow progress, but I'd hoarded some old English Oak panels when my neighbour passed away a few years back & the family gave me some of John's garage shelving. Rough sanded the top face & routed out two rectifier tube holes, before cutting down the panel sizes. The wood is covered in marks & age patina, but hopefully will mostly clean up & the rest will maybe add to the 'rustic' patina' of the finished case-work... Oak has lovely grain & can present wonderful, aged, characterful 'figuring'. 
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Post by Owen Y on May 8, 2020 22:01:31 GMT 12
All the main Oak bits cut out now, together with the plywood internal 'frames'. I have a scheme to put it together without visible screws etc, but just have to figure out an access panel idea for future access to the innards! 
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Post by Owen Y on May 12, 2020 11:46:38 GMT 12
Panels radiused & rough sanded. Some minor filling to be done. Almost ready for assembly... 
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Post by Owen Y on May 14, 2020 13:48:56 GMT 12
Americans make some good tools. The 'Forstner bit' (invented by American Benjamin Forstner in the 1880s, initially for gunsmith use) has appeared over here only in recent years (20-ish? to my knowledge). You can cut, in wood, nice clean-edged, flat-bottomed, round holes. Here, countersinking a hole in 18mm thick Oak , for mounting the on/off switch - which was intended for mounting through a thin metal panel.  
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Post by Owen Y on May 16, 2020 11:42:03 GMT 12
Installing valve sockets: Previously, I've used these sort of chassis punches for making holes for sockets, but these are good for only thin sheet metal, as they work using a shearing action through the sheet.  But these Tungsten Carbide Tipped (TCT) hole drills are much better & will get you through thicker panel-work - 2-3mm aluminium or possibly even steel, should be no problem. My ones are Chinese-made, inexpensive originally from an online HK store. (Or you can use a 'Step Drill' bit - one drill does all different holes diameters, I have not tried these.)  28mm (1-1/8") is good for octal, UX4-pin. Or 32mm (1-1/4", depending on socket design. (19mm (3/4") for 9-pin, 38mm (1-1/2") for some bigger ceramic sockets.)  (Using here a NOS McMurdo UX4-pin socket for a 5Z3 rectifier.)
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Post by colinf on May 16, 2020 20:06:27 GMT 12
I usually use a stepped drill bit on slow speed on the drill press, works fine. Too fast a speed makes it chatter and you get an imprecise hole. (Not to mention how loud it is!) The TCT hole drills look cool, might give some a go :-)
AMR-iFi R&D
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Post by Owen Y on May 18, 2020 10:52:59 GMT 12
Slow progress as usual - mounted the rectifier sockets on the top plate (boards) - spaced with an air gap around sockets to accommodate the screws & for some airflow 'chimney effect'. (Tube cooling is not an issue, but it's good practice & might help keep some heat off the wood.) 
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Post by Owen Y on May 29, 2020 13:09:13 GMT 12
Glacial progress, but taking shape...  (One of the 2 (mirror-imaged) PSU boxes.)
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Post by Owen Y on May 30, 2020 21:25:13 GMT 12
The 2 boxes, each with a hole in side panel for the DC output socket (3-pin XLR) - using a Forstner bit again. 
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Post by Owen Y on May 30, 2020 21:38:50 GMT 12
Because the boxes are narrow, access later for servicing etc, will be awkward through the front or rear. The top will be wired with tube socket & on/off switch. So, I need to have a removable side-panel. It's done with a bevelled wood cleat on the side panel & a mating one on the box frame. Then locked with a couple of screws through the bottom panel. I thought it might be tricky to implement, but it worked without headaches.  
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Post by Owen Y on May 30, 2020 21:44:49 GMT 12
The whole thing is screwed together using square-drive screws - 'Surefast', the type that builders & tradies use. (Mainly just because I had half a jar of them left over.) And a bit of wood glue (aliphatic resin) here & there. Re-purposed old Oak outer panels with inner pieces from scrap 12mm & 17.5mm pine ply. 
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Post by sadface on May 30, 2020 21:56:25 GMT 12
Those are going to look stunning!
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Post by Owen Y on May 31, 2020 15:40:11 GMT 12
Thanks sadface - this was meant to be a quick exercise. Other more interesting things are still waiting to be done.
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Post by Owen Y on Jun 1, 2020 12:03:58 GMT 12
A quick sealer coat all over before installing the parts. I have a problem with one panel. some filling needed. Ahh, long weekend. 
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Post by Owen Y on Jun 2, 2020 11:14:21 GMT 12
When filling a couple of historic nail holes (this is old, s/h wood) with glue & wood chips, I found that the mixture turned black! A known phenomena is that some woods with high tannin content (Oak is well known & this I think, is the origin of 'black Oak') will turn black when exposed to water + iron/steel - I had used a steel blade to mix & fill. Black staining you see around ferrous nails in wood is also caused by this. So, I had to dig it out & re-fill (using a SS knife this time) - this time, no blackening. [Edit: Only the original historic blackening in the wood remains, as it did before filling.]
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Post by michaelw on Jun 2, 2020 15:01:30 GMT 12
just leave the holes ? i have several pieces made of matai recycled from the old PN opera house and the nail holes etc add extra character to the pieces.
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Post by Owen Y on Jun 2, 2020 17:37:39 GMT 12
Yup, pretty much, the hole stains will be part of the 'patina' re-purposed wood.
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Post by colinf on Jun 2, 2020 22:01:57 GMT 12
That’s interesting.😀
AMR-iFi R&D
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