Hacker Sovereign 2 RP25B power socket.

it will have three connections

1) Common centre pin. May have been negative. Most modern PSUs are +Ve centre pin, but "Universal" types are reversible.

2) outer barrel of connector, goes to radio power switch. May have been positive.

3)Switch contact that goes to battery. May have been positive.

It's likely any 250mA or higher current PSU at unregulated 12V (minimum) to regulated 20V (max) is fine as the Batteries when fresh are over 10V each and the exhaustion point is 0.9V to 1V per cell, = 6V. There is no such thing as a 9V battery when it's Zinc Carbon, Zinc Chloride or Alkaline.

If it's not a regulated PSU, then a 500mA or 1A 12V PSU could be 16V to 18V at the current the Hacker takes.

It's centre-negative. Take care with modern PSUs! Consider adding a diode in inverse-parallel - the rear of the volume control is a good place for that. Most modern PSUs will survive a brief overload, and if they don't - tough

Don't use an unregulated supply; it will hum!

CPC used to sell an 18V 400mA unit that was ideal for these, but actually there was a small amount of background hum. The Hacker VP408 is a better PSU in this regard, but they can be expensive on eBay (I've seen them fetch more than £25).

If you're a member of the Hacker Radio Yahoo group, you'll find the schematics of the VP408 PSU, and it's pretty easy to build one.

I'm not in a position to photograph one of mine at the moment - maybe later. Perhaps it would be easier to look at what you already have, then I could advise...

All the best,

Mark

I once built a 9V PSU into a PP9 case and ran a flat mains lead through the corner of the back as it is just loose fitting enough to do this. It worked very well. A new PP9 to restore to original
If the center tap is required just build two of them with a common mains lead.
I would put the diode in series so that the set will just not work if the power is the wrong way round.
There would be a bit of an umm if you connect an AC eliminator but no lasting damage.

I did the same - my first digital DVM was an Advance with a tiny 3-digit LED display, and that ate PP9s like they were going out of fashion. Back then, PP9s were metal cased, and I didn't earth the case. I still have it, and show it to people when discussing electrical safety! Will try to remember to photograph it when I next do that in a couple of weeks time...

Whether to put the diode in series or parallel is something we all have to decide for ourselves. Having thought it through, I prefer parallel with 18V sets, as they are more likely to be connected to a weedy "wall-wart" PSU than anything else, and this has the advantage of not losing 0.7V across the diode. There's no convenient way to arrange the diode to be in series with the external PSU only, so that drop is lost on battery operation as well. For the 12V sets, you might consider series connection (on grounds that the set might be connected to a car battery), but the voltage loss is more significant. Of course, 12V accessory plugs generally have fuses in, so I'd probably stick with the parallel connection...

Back in the day, there were countless circuit ideas and projects published in the electronics magazines that attempted to solve this problem - some using relays that only pulled in when the polarity was correct, others attempting to use semiconductors, but in some clever way that avoided the losses. Some were very complex indeed! It's a non-trivial problem. Seems to me that a bit of care and attention is the simplest solution...

As I say, it's up to the OP to decide, but those are my thoughts on the subject, which may (or may not) help his decision. Of course, PP9s are so very cheap these days that it's perhaps easier to avoid the question altogether

Cheers,

Mark

You can put the diode in series only with middle pin and not in series with battery. An 1N5418 or 1N5419 will be about 0.15V to 0.3V drop. But a 1A to 5A diode across the supply was common enough on CBs.

An unregulated 12V AC to 15V AC and full wave bridge with 1000uF + 1000uF and about 33 Ohm to 47Ohm series between them should work with out much hum. (possibly not audible).

Or for a regulated PSU a 7812 and 5.6V zener in series with "earth pin" decoupled with 100nF and fed with 1k from the supply will give 17.6V. A 5.6V zener has lowest temperature drift. 15V AC is likely too low to feed that, so 20V + a full wave bridge is 28V on no load. Likely a 470uF 35V on regulator i/p enough. Decouple 7812 o/p with 100nF. A 7815 and green LED replacing the zener will give about 17.2V and work well too.

+Ve to barrel
-ve to pin

Where are these cheap PP9s Mark, apart from the ones I refill at 75c per PP9?

I get mine from CPC for around £3 each. Through work, the same batteries from a different supplier come in at less than £2, but I've not found a way of placing orders with them directly on those terms yet. As usual, no use for you where you are.

Over the years, I've seen countless ways of converting these to mains. I suppose that C-R-C is the most commonly encountered approach, but they always hum - even with two lots of 4700uF. These sets need an absolutely clean supply - PSRR wasn't a consideration in the original design. I don't know what is inside the Stonetronics PSU that CPC used to sell, but they are well-regulated and seem fairly clean on the 'scope - probably a 7818 or a "lifted" cheaper variant, or perhaps an LM317T - it'll be something cheap and simple for obvious reasons. But, on the radio they hum! As mentioned, the Hacker VP408 is my recommendation - but even that is noisier than batteries.

Obviously, DC precision is not the issue. If it were, I'd put an 1n4148 in series with the 5V6 Zener. But we're just showing off at this point

Yes, a diode on the centre pin would indeed work, but as I said, there's no convenient way of doing it. You'd see it when you opened the back, and it wouldn't be pretty. Given that we're talking about restoration, that goes against the grain for me. An inverse-parallel diode can be hidden behind the volume control, which floats my boat! But, that's just my view - perhaps others don't mind their sets being modified like that. A different conversation altogether, and one where there would probably little in the way of consensus if previous conversations elsewhere are any indication

Well, I haven't fitted either diode on my RP18. But then it's probably not meant to have a socket. I could take it off and patch using a piece of cloth from insides.

From what I've seen of yours, it looks like a dealer retro-fit using Hacker parts, so while not original, it's not a "bad thing" by any means. In your position, I'd probably leave it

If you were thinking of changing it, keep an eye on this eBay seller: http://stores.ebay.co.uk/Interesting-Electronics - every now and again they offer cases for silly money - I bought a near-mint RP18 case from him for less than a fiver. In months to come, I might end up with a spare central carcass; in which case it's yours for postage.

I've bought stuff off him and nearly bought a case to make a Russian Rod Pentode radio in.

It's centre-negative. Take care with modern PSUs! Consider adding a diode in inverse-parallel - the rear of the volume control is a good place for that. Most modern PSUs will survive a brief overload, and if they don't - tough

Even a series diode would probably be OK here.

I did the same - my first digital DVM was an Advance with a tiny 3-digit LED display, and that ate PP9s like they were going out of fashion. Back then, PP9s were metal cased, and I didn't earth the case. I still have it, and show it to people when discussing electrical safety! Will try to remember to photograph it when I next do that in a couple of weeks time...

Those were Advace DMM2s or DMM3s(larger display). I still have one of Advances own PP9 sized eliminators kicking around here somewhere.

Al

Thanks for that everyone. Still wouldnt mind some pics if that is possible.

Hi,

I've just posted some on UKVRRR: http://www.vintage-radio.net/forum/show ... post538003

For all I know, it might be you asking the question.

I put them there simply because their file upload automatically resizes images as they are uploaded - I'm not sure if this forum does that, but I'm in a bit of a rush and didn't have time to find out.

Earlier in the thread, I said this:

Perhaps it would be easier to look at what you already have, then I could advise...

...and I still stand by this. But hopefully those pictures help. If someone wants to bring them across and add them to this thread, that's fine with me.

Better dash

Mark

Totally identical to the socket and wiring on my RP18, except there is no decoupling capacitor on mine.

Mark's pictures a little edited

Thanks for that Michael and of course Mark.