A new RP25 in the family

[Mark Hennessy]

When I got back into radio restoration a few years back, I was glad that I'd saved a fair few Ge transistors from my childhood. I also keep a look out on eBay and similar places - a lot are massively over-priced, but there are occasional bargains to be had. And you there are no shortage of total basket-cases on eBay, and a complete radio (including postage) can be had for less money than the bare transistors in some cases.

But yes, change that electrolytic first. Then perhaps try a Si PNP in the oscillator position - it might be more reliable than the AF239 with the new capacitor. If you can find an AF12X or AF11X, then so much the better. I assume you're aware of the tin whisker issue with the latter, and how you might "fix" it?

And yes, ribbon cable is your best bet. It should be reliable enough, but you can always parallel up cores if worried. How nice to find someone that doesn't just drill a hole in the side :-)

Hope this helps,

Mark

[boiss]

OK Mark,
The C21 sorted the Instability. Re-aligned the MW so that L5 was set OK however still no oscillations from TR1 on LW. Had a look at some of the silicon that I had in the drawer and picked a MPS6518, F 150MHz and HFE 150. Swapped out the AF and checked the MW alignment again. Still nothing on LW. Changed the biasing Rs from 1K2 and 6K8 to 10K and 18K as per the RP25B. Whoopee OK ! aligned the LW Great, works fine now on all bands. I think I'll change all the electrolytics in the coming weeks after the C21 performance. (I changed them all on my Sony 7600 a terrible job but worth it)
I'll see if I can get a film ribbon from an old scanner otherwise the ribbon will have to do. I was thinking of some sort of induction system like my toothbrush charger, has anyone done this ? Holes No Way!!!!!!!!!!!!!!!!
I had a look at the Hacker radio group and noticed that you mentioned about probs with the LW LO for the RP25/35 but could find nothing in the manuals on the site.
Anyway thanks for your advice and help, much appreciated.
BRs
Mike

[Refugee]

I was thinking about this and may have an idea.
Does the set has a carry handle?
I was thinking of taking power from the fixing screws. This would mean having a wall bracket like a cradle that the handle rests in when listening on external power from the ends of the bracket.
It would not work if the handle is all metal.

[tiv48]

this may be interesting electric toof brush induction chargeing
http://www.youtube.com/watch?v=JJgKfTW53uo

[Mark Hennessy]

In my experience, if the remaining capacitors are the light blue Philips, or light grey types from Japan, they are probably OK. Anything else is suspect. Older red Elkomolds or similar were used on the AM IF PCB until extremely late in the Sovereign II run - no idea why...

Good idea about the handle screws, especially as they are both insulated from the chassis. But yes, the handle is metal. The set in question is probably the earlier type that is easily removable. but even so, you'd probably get fed up with that.

Neat idea re. electric toothbrushes, but I'm not sure you'd get the coupling - the wooded cabinet is quite thick. I've had similar thoughts in the past for other projects but never got around to investigating.

Ultimately, providing a DC input might be more trouble than it's worth. We have an RP25 in the kitchen; it's used daily and batteries last around a year. PP9s are cheap. When exhausted, they can be taken apart and holders can be fitted - you can actually get two 6AA holders in that space. You could use rechargeable AAs in there, of course.

Oh, the thing about LW oscillator failure should be in the RP25 manual, in an addendum. Hacker also sent a letter to dealers covering the issue, and this letter is in the archive. Essentially, the fault was caused by problems with aluminium screening can covering the oscillator. Hacker were relying on the can to carry an earth connection across the PCB - but in some examples the riveted connections could go high-resistance. The fix was to add a short length of wire on the reverse of the PCB, joining together the two pins. Later versions had a revised PCB.

All the best,

Mark

[boiss]

Mmmhh, Bit of experimenting wanted here, maybe a flat coil with a ferrite core that could sit under the radio and the same under one battery, I've got a motor from a VCR and the coils are flat on a metal panel maybe with 2 of these???
cheers for now,
Mike

[Nebogipfel]

Post deleted PM sent

[boiss]

After doing a bit of research it looks like it is do-able. It relies on the inductors on the Tx and Rx sides being resonant. Certainly for the 1 to 1.5 cm spacing involved the efficiency should be quite high. Here in Spain PP9s are not readily available so I have to order them from RS along with some high power MOSFETs to try out the idea. The ideal solution once these batteries go down would be to replace the internals with 6 x AAs and fit the base of the batteries with an inductor and other internal circuitry to enable charging and/or radio operation. This would require a base panel into which the turntable slots with 2 inductors in the base. A sensor would measure the output current in order to ascertain the charge status.
Once I get the MOSFETs I'll do some experimenting. More to follow, maybe a new thread would be an idea.
BRs
Mike

[AlanBeckett]

Mike,

I hadn't realised you were in Spain - Doh.

I made a rechargable PP9 using an old case and AAs, plus a series restor - I really would advise a series resistor or fuse for safety as the S/C current of the stack can be pretty horrific.

There's plenty of extra room in the case to add extras.

Good luck with it.

Alan

   

[Mark Hennessy]

Hi Nebogipfel and Boiss

Just to confirm that I've finally caught up with myself, and your sets are now in the database. Sorry it took a few days - I was away for a few days last week, but that's no excuse really. Thanks for the details!

Cheers,

Mark