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Old 27th Jul 2016, 5:24 pm   #1
SeanStevens
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Default Imitation - 9V Hacker Power Supply

I had been talking to Ian (Hermit6045) about building a power supply or two recently for powering up Roberts and Hacker radios. I can get PP9s – but it would be nice to have an alternative to the battery if the darn things go flat.
No sooner had we discussed the possibility of making a supply when a thread appeared on this forum showing a genuine Hacker power supply, in the shape of a PP9.

https://www.vintage-radio.net/forum/...ghlight=hacker

Now, if Hacker could make this back in the day, there surely was no reason why a hollowed out PP9 case could not be filled with modern gubbins to do the same.

Ian spotted a 12v transformer being sold at Maplins (no connections to the company etc.) that stated that it was ‘sub miniature’. Before the transformers arrived we started prototyping (using a handy spare 12v transformer) and got some good results using a 9v voltage regulator (7809), some capacitors and a full wave rectifier. A dead stable 9v was obtained and it generated no extras above normal mains noise. Also as the case would ideally be sealed, the temperature of the components was checked to ensure no overheating would occur. Due to the tiny 3v drop required, not a really noticeable temperature rise was noted after a good run of a Roberts R200 at high volume.

Unusually, when Maplins delivered, the 12v transformers turned out to be a 12-0-12 (ie 24v), so the design changed a little to incorporate separate diodes (1N4007) as opposed to the bridge rectifier in prototype 1.

A bridge rectifier was used in the prototype because we only had a transformer that had a non-centre tapped secondary. The Maplin transformer was centre tapped so it was possible to use a couple of 1N4007 diodes with the transformer centre tap being the 0 volt rail. Saving some valuable space in the process.

Once the reviewed design was proven the task of getting it all to sit inside a PP9 case was explored. Now a PP9 is a big old battery, until you start trying to cram stuff into it, when it suddenly becomes an ‘inverse Tardis’ and makes life difficult.

Wanting to make this thing safe, a fuse holder and fuse were incorporated. These things have quite a depth to them, so planning the space layout within the case was important.
A guillotine was used to cut a strip of aluminum of around 1mm thickness the width of the battery – a bend of 90 degrees applied to one end to allow affixing to the lid of the PP9 – holes were drilled to mount the transformer and some tag strip (we found that 5 tags were sufficient) and off the construction went. The mounting of components again had to be carefully though through, as space is not abundant. Also, the exit point for the mains cable is contentious. Some Roberts Radios (R200 – R300) require the wire to enter at one side of the battery case – while the Roberts R500 ideally has a top entry for the mains. My Hacker wants a top entry for the mains too, so the first completed model went to me for my Hacker Sovereign.
The second construction went well – and lessons learned from the first construction (having been forgotten) were learned again! After ‘hot glue’ mounting the aluminum plate to the lid I realised I had totally forgotten to drill the hole in the lid for the fuse holder (possibly because the second model was a ‘side entry’ mains version) – but hey-ho, it made for some colourful language!

There are some questions still unanswered for this project.

The entry point for the mains cable – ideally it would suite all PP9 radio candidates – but this might be impossible.
To fix, or not to fix. The lid is currently loose on both examples. It is highly unlikely to want to open these up in the future – but who knows. Also, unless the lid is glued, it would need bolts or screws to secure it. The lid is ‘complicated’ enough as it is, so the jury is out on bolts or screws………
Mains noise – the R200 has a low slung ferrite rod. This picks up mains noise present due to the proximity to the antenna. Although only ‘in-between stations’, this was annoying. We proved that it is most probably not the fault of the design……..


Thanks to Ian for his knowledge, his ability to stay calm while I’m climbing the walls and having tools above and beyond the call of duty. Without the guillotine, tin snips and general hole making devices, I’d still have a handful of components and a frown.


SEAN
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Old 27th Jul 2016, 6:06 pm   #2
Jonster
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Default Re: Imitation - 9V Hacker Power Supply

Looks good, great idea. I would also add low value ceramic caps to decouple the input and output of the regulators, nice and close to the pins as well as the electrolytics, and mount the regulator to the aluminium to give a bit of heatsinking, I would imagine that unless the radio is up full blast it won't draw more than 100ma or so so should be OK.
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Old 27th Jul 2016, 8:40 pm   #3
mhennessy
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Default Re: Imitation - 9V Hacker Power Supply

I did a similar thing many years ago. That used a metal-cased PP9, so was pretty dangerous, but it went into the plastic case of an Advance DMM, so was safe enough when in use. Today, I show it to people at work as an example of how not to build a power supply! I'll try to remember to take some photos tomorrow.

What you've produced is pretty nice

Suggestions?

I'm not sure about hot-melt glue. I've used it for things in the past, but I haven't built up much confidence in it - especially when in "tension", as it is here. So I'd prefer use a couple of small countersunk screws to secure the lid to the chassis. It might be possible to use the fuse holder to help secure it, of course...

Also - and I know this might be easier said than done - have you considered making the chassis a U-shape, with two bends? Done to the right dimensions, the other fold could reach the bottom of the battery - and then you could add a couple of screws to secure that from underneath. This approach neatly solves the problem of how to secure the lid.

As Jon says, I'd worry about the regulator. Bolting it to the chassis is the easiest/cheapest approach, and still compatible with the tagstrip approach.

You're right about the cable entry conundrum. One approach might be to secure the cable to the chassis, and have two exit holes. But changing holes will involve having to remove the mains plug - so not all that convenient. A pair of "figure of 8" sockets on either end might work, but you'd need to include a double-pole selector switch for safety. Plus, the lack of flexibility in the plug might cause problems.

If you did away with the strain relief (just a grommet would be fine, as this is inside a set), then the cable can be laid alongside the battery in most cases.

Another tip: if you don't enjoy metalwork, copper-clad PCB material is a viable way to build projects like this. It's relatively easy to work, and soldered seams are pretty strong. A few years back I came close to building a powered speaker in a PP9 case (to use for travelling with my MP3 player), and had planned quite a neat arrangement involving bits of copper-clad FR4 soldered together (along with some Veroboard to hold the amp. The 2" Visteon loudspeaker sounded surprisingly OK in that size enclosure with a bit of EQ. Perhaps I should crack on with it - just for fun

Again, an excellent job - well done

Mark
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Old 27th Jul 2016, 10:43 pm   #4
Phil G4SPZ
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Default Re: Imitation - 9V Hacker Power Supply

Excellent work, Sean and Ian, and very neat.

In my own R200 I have a PP9 case with a 6 x AA cell holder inside. Still dearer than running off the mains, but cheaper than replacing PP9s!

Well done.
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