Hacker Sovereign II RP25

[radiovintageman]

I've in some way messed up my wife's treasured and immaculate blue RP25.  After changing batteries and carefully setting audio board quiescent current to 3mA and midpoint voltage to 8.9V I've got very bad scratchy distortion at high volume.  I've upset her a great deal but don't know what I've done to it.  It sounds a bit like a damaged loudspeaker cone, but there's no problem at lower volumes.  The 400 microfarad L/S coupling cap seems OK.
Anyway she won't let me touch it again, so has anybody got an immaculate blue Sovereign II that I could buy? They're rare I know, but I'm prepared to pay big £ for the right one just to get her a replacement.

[Refugee]

You have broken that rule.
"Don't touch what is not broke".
Those pots you adjusted have sat there and corroded in the air even though they may still look new.
You would need to get them back to where they were before which is almost impossible.
New pots is the way to go. Modern ones are enclosed and less likely to go noisy.

[BusyBee]

It would do no harm to try cleaner. I find that Duck oil works well, being a little thicker than switch cleaner. I have dismantled the pots before and cleaned out.

Tracy

[Mark Hennessy]

If the quiescent current and mid-point are still OK after the adjustments, then the pre-sets are likely fine. They're actually pretty OK in these sets, but sometimes benefit from a tiny bit of switch cleaner.

The first thing I'd check is the 5 pin connector. These are notorious on these sets. You might need to squeeze up the contacts on the PCB, and/or you might have bad soldering on the PCB. The plug itself is usually OK. Again, a bit of switch cleaner is a good idea.

The symptoms from a bad connection there are many and various, and it might not be the problem in this case, but that's the first thing I always check.

Having said all that, I'm not sure about the original question. Is this a "wanted" thread, or a "help to repair" thread? The wording implies the former, but the forum choice implies the latter. If the OP wants another set rather than help with repair, I'll move this into the Wanted section.

Also, if you already have an immaculate RP25 that just needs repair, you don't need an immaculate replacement. Anything would do, providing it's electrically good.

Worst-case, assuming you really don't want to attempt a repair, you either need a replacement A205 (the audio amp) or another speaker (less likely).

Or you need someone near to you who can repair the existing set.

Either way, spending upwards of a couple of hundred to replace the whole set sounds like a bad idea from every angle. I can't believe that's the only way to make it up to your wife - surely getting the original repaired - with all of its history and association with her - is the answer, and a replacement just wouldn't be the same, no matter how mint it might be? If anything, you'd be even more in the doghouse, with a lot less cash in the bank!

[radiovintageman]

A lot of very good advice, thanks refugee, Mark and Tracy. But what do I do if she is adamant that I don’t touch it again. Yes, I’ve dealt with the 5 pin plug and socket which were causing noise when the set was moved, cleaned and lubed the intermittent LW switch, changed the dodgy C1 and bad C9, run solder around any joints which looked suspect It was fine after that until it suddenly wasn't. Yes the presets could be dirty, but there was no difficulty when setting them up and no fluctuations when set. A fully checked replacement audio board from a scruffy donor is probably the easiest way rather than checking every component in this one, but it’s going to be a long time before she lets me touch it! She said she would however accept an immaculate replacement! Sorry, I’m being boring about this, but this particular gremlin caused havoc! ☹️

[Mike Watterson]

Also, if you already have an immaculate RP25 that just needs repair, you don't need an immaculate replacement. Anything would do, providing it's electrically good.

Worst-case, assuming you really don't want to attempt a repair, you either need a replacement A205 (the audio amp) or another speaker (less likely).

Or you need someone near to you who can repair the existing set.

Either way, spending upwards of a couple of hundred to replace the whole set sounds like a bad idea from every angle.

Agree 100%.

Obviously after some time has passed there needs to be some negotiation and discussion.

A scope on the speaker and seeing what sort of distortion is happening at higher levels might be enlightening? Maybe it's running SE instead of push-pull?

[Mark Hennessy]

Sadly, marriage guidance is probably a bit beyond the remit of this forum

Either way, this is likely to be technically easy, but as is so often the case, the human factors are the problem. As Mike says, hopefully time will help. From what you've said, you're clearly not a complete beginner, so you're in with a good chance of success when the time comes. The service manual is available free of charge from the Hacker Radio group, and physically they are one of the easiest radios to work on. Between here and the Hacker Radio group there's no shortage of people who can help you once things have eased. There's no harm in preparing for that eventuality by studying the service manual (if you haven't already) and asking questions in advance.

https://groups.io/g/Hackerradiogroup

The schematic of just the A205 amplifier is here: https://markhennessy.co.uk/articles/hacker_a205.jpg

It's pretty reliable on the whole, but the AC128/176 can suffer from tin whiskers and reduced gain. The latter is what caused my immaculate blue example to distort at higher levels (no, it's not for sale!). If you decide to obtain new replacements, watch out for the modern version that doesn't quite fit the heat sink clips: https://markhennessy.co.uk/articles/to1_...nd_new.jpg

Good luck!

[Mike Watterson]

Does the RP18 use the same or nearly the same audio board?

I do remember swapping an audio board and then replacing a lockfit transistor with a regular TO92 part on a pair of Hackers. One was certainly an RP18.

[Mike Watterson]

The BC148 must have been in an RP25 (though 2x BC108 is listed) as the audio board in the RP18 is 100% Germanium. I looked in the attic, but the Hackers must be in a box rather than on the shelves. So the audio boards are different but somewhat compatible.

[Mark Hennessy]

Yes, they are quite different, but for testing you can connect either amp to either radio - the 5 pin connection is identical. The RP18 amp is larger than the RP25 one, so couldn't stay in an RP25.

And yes, although the RP25 manual says BC108, I've only ever seen the Lockfit BC148 in there, even in the earliest examples. I fit BC108s as replacements, along with a bit of green sleeving on the base, like the other transistors. As it's what the manual says, I'm fine with that!

Similar comments apply to the RP38A amplifier: https://www.vintage-radio.net/forum/atta...1276089300 (although hosted elsewhere, that set and image is mine - indeed, it's the one in my avatar)

Electrically, the RP38A is very, very similar to the RP25 amp. The earlier amp was more complicated, with many more electrolytic caps (and usually they were the blue "Daly" types that are change-on-sight). They did a good job with the A205 design. It was used in many other later sets with relatively minor changes over the years.