Hacker Sovereign II RP25

[radiovintageman]

It's possible a thaw may soon be seen in the XYL since she's released she can still listen perfectly well at moderate volume level! Anyway I've found a cheap but complete RP25 and I already have a download of the service manual so I'll deal with all the suspect failure points on the audio amp. from the donor, test it, and when the time is right fit it (that's if the speaker cone isn't shot) to the pride and joy. Thanks for your all your help guys, look forward to any chance to contribute positively in future.

By the way I didn't say that I was in broadcast engineering and management in transmitters, studios and OB's for nearly 50 years, have forgotten most of the analogue stuff and never learned enough about digital.

[ppppenguin]

Good luck with your Hacker and also with your XYL. As Mark says, we're not talking about anything hugely complex. Mark mentioned changing the Lokfit BC148 but didn't say why. All Lokfit parts are liable to failure, probably due to mechanical stresses in the packaging. Almost any small signal NPN silicon transistor can be used, but the BC108 (metal TO18) and BC548 (plastic TO92) are direct equivalents.

By the way I didn't say that I was in broadcast engineering and management in transmitters, studios and OB's for nearly 50 years, have forgotten most of the analogue stuff and never learned enough about digital.

If you haven't already, please have a look at the BECG's website: www.becg.tv You're close enough to us that you might want to visit and awaken some old memories. Your XYL might enjoy the adjacent antiques centres too. A recent acquisition is part of a Marconi BD272 which was Sender 93 at Woofferton. There's even a risk that you might want to join in the fun

[radiovintageman]

Yes, thanks for invitation to Hemswell, I look forward to a visit. The BD272's were coming into use at Skelton while I was there. Anybody remember the SWB18's with the trolley coil assemblies being sweatily changed over at 3 a.m?

Anyway regarding the Hacker RP25, it's hard for me to say this, but it was one of the"new" PP9's. Although showing good voltage at low load it couldn't deliver the current for high output level. On Long Wave I suspect the local oscillator was cutting out as the load came on, producing a kind of motorboating effect? Never buy an apparently new shrink wrapped PP9 if the date stamp isn't clear!
I'd thought about it, had a fortunate guess, and a local "thaw" enabled me to change the batteries again and now peace is restored.
Don't know whether I'll tart up the intended donor RP25 and offload it or keep it for spares. Let me know if anybody needs some parts?

[ppppenguin]

Well done for finding this. In accordance with Rule 1 of faultfinding I assume you'd already checked the supply voltages and found them OK.

Since PP9s are both expensive and scarce some people get 6x AA holders and put them inside an old PP9 case.

[radiovintageman]

Yes I’ve been stuffing old PP9’s for a long time, but decided a pair of real ones would be more appropriate for the pristine treasure. I believe good originals should be worth about 5000mAh while an alkaline AA cell is about half that? Better than an out of date PP9 though!

[Mike Watterson]

Depends on load.
The 5000 mAH is on light loads, unspecified, because it's layer cells.
The Alkaline AA should be 2700mAH (Varta, Lidl, Aldi etc), but is very much lower resistance than layer or Zinc Carbon, but not as low as NiCd or NiMH. The low cost Value Duracell is a lot lower capacity than regular Duracell. Some Panasonic (but overpriced) might be 3000 mAH. I don't buy Energiser or Duracell now.

It's not impossible that at low volume on a Hacker you get equivalent to 3,500 mAH on really good Alkaline AA as the 2700 mAH rate is based the standard IEC load test for AA.

Also Alkaline in cool conditions have hugely longer shelf life. Make sure springs not too strong as many Alkaline cells have now poor seals on negative plate (can is positive) and will leak. I've had to add parcel tape or fake cover to some brands of Alkaline D cells in vintage set as the chassis or negative can pierce the too thin plastic film on some.

I've also done card PP9 and other PPx larger than PP3 for vintage sets; remember that the red and black are reversed when making a battery pack! Sometimes I remove the plastic cover and rewire. Easier to glue to fake case with cover removed.
http://www.blaukatz.com/tables/batteries-in-2014/

I've only ever seen out of date PP9 in Halfords. Occasionally B&Q has massively overpriced Dial brand (Their own obtained by Kingfisher who own them & Screwfix) PP9, so I don't buy those anyway.

All the PP range:
http://www.blaukatz.com/tables/layer-batteries/

More than 2500 mAH may be optimism on NiMH, and most of the 2700 mAH seem to self discharge rapidly. Higher voltage NiMH/NiCd packs tend to destroy one or two cells by reverse charge if a cell is flat before the others and what ever it is keeps running. I've had to replace the 12V pack twice in one piece of test gear (10 cells).

[Murphyv310]

Hi
2 X 18650 li-on batteries per PP9 case.
Make them removable and charge on USB charger you can buy online
Get the pip top 18650s as they cut off at 3v approx. The radio will still operate well before the batteries shut down.

[ppppenguin]

At 3.6V nominal per cell isn't 7.2V a bit low for replacing a 9V battery?

[Murphyv310]

At 3.6V nominal per cell isn't 7.2V a bit low for replacing a 9V battery?

They charge to 4.2v and take a good few hours to drop to 3.7v. I run one here and have no problems until the batteries get to just above 6v.
Or three in one box and two in the other, that though would give 21v fully charged which is slightly too high as new PP9s will give 20v, a diode in series is a way out of course giving 20.4 fully charged, the USB chargers though will give the batteries 4.1v each = 20.5v again a diode brings this to 19.9v.
Personally I'd still stick to 4 batteries.

[Mark Hennessy]

The RP25 is quite tolerant of low batteries, so I'd expect it to be OK.

That's true of most Hackers IME, but the Hunter RP38A is a bit more fussy about supply voltage if you're in a marginal reception area like around here. Can be helped by replacing some of the carbon comps dropping the rails and doing a full RF/IF lineup, but while one or two are excellent, most samples are not as good as an average RP25 or similar.

(A good friend used to have an eBay business selling radios, and Hunters were his best seller. As such, I've worked on dozens of them. I did make systematic efforts to work out why they were so variable, but ran out of steam before reaching any firm conclusions. Hopefully enthusiasm for them will return when I'm less busy elsewhere!)