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Old 12th Dec 2018, 11:28 am   #21
Herald1360
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Default Re: Hacker Sovereign II RP25B

Quote:
Originally Posted by Hunts smoothing bomb View Post

........

It might be a good idea to charge them separately though as series charging can bring on problems if their internal resistance is not matched, this could then seriously "over volt" the other battery.

Cheers
NiMH batteries already contain several cells in series, adding another battery in series
doesn't change this fundamental arrangement, just the voltage compliance required of the constant current source used to charge them. If the charging current is C/10 or less, they won't come to any harm left on charge for 24 hours or so. If the voltage split between the batteries is seriously uneven at the end of this time, then one or the other or both was dead already; series charging won't have caused it.

Parallel charging is potentially bad news, though, since any difference in the batteries' on charge voltage can cause unequal current sharing and possible damage to cells from overcharging or simply an excessive time to charge one of the batteries as seen here.
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Old 12th Dec 2018, 12:01 pm   #22
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Default Re: Hacker Sovereign II RP25B

I gave the set a good run last night on a Classic FM concert. It was a case of my elderly hearing not being up to the set, rather than the other way round.

These batteries are lovely: they still match, each giving 9.2v on load this morning on load (nominal voltage stated as 8.4v). I'm very pleased that having these will remove the need to regularly go looking for new PP9s.

I've now printed out the manual and got the set apart. First job: to look at the dial calibration. I checked the quiescent current on FM. It was a touch high at 24/25mA. But then the battery voltage is presently a little on the high side, so I'm not panicking. Later on, I'll take it down very slightly.

Steve
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Old 12th Dec 2018, 12:13 pm   #23
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Default Re: Hacker Sovereign II RP25B

Charging 2 sets of "batteries" in series relies on each battery being the same age, quality and internal resistance. The cells in each battery will be the same age and had the same use. It is also likely that the other battery has had similar use as they were used in pairs, so it should be OK to charge them in series.
You will need an initial voltage of at least 30v and a minimum 5 watt resistor of about 100 ohms. The higher the voltage of the charge source (obviously the series resistor will need to be larger to limit the current) the more stable the constant current will be as the rising battery voltage will be less significant compared to the supply voltage.
The above arrangement should give you an initial charging current of about 150mA falling to about 100mA when charged.

If you decide to charge them in parallel (as you have a 13.8v supply) it would be better to have a resistor in series with each battery.

Mike
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Old 12th Dec 2018, 12:38 pm   #24
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Default Re: Hacker Sovereign II RP25B

In the end, I remembered I had a controlled current 0-30v power supply sitting under the bench, and used this for the bulk of the series charging, set to a constant 150mA, working at about 20v.

Quote:
Originally Posted by mhennessy View Post
Yes, the pointer datum is the first thing to check. You can normally correct it by moving "pulley B" along in the slot provided. The instructions in the (excellent) manual tell you to set it so that the pointer just reaches the right hand end of the scale openings.
I haven't yet found this "pulley B", but it looks very tempting just to slide the pointer along the cord (arrowed). I'll keep looking...

Steve
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Old 12th Dec 2018, 2:25 pm   #25
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Default Re: Hacker Sovereign II RP25B

Found "pulley B"... in the end a combination of both measures was needed to correct the pointer travel error. The pointer now comes to rest at the correct position, and pulley B is in the centre of its travel.

As a result, the calibration on both VHF and LW is now very close. On MW it's still a bit out, so some tweaking is called for.

Steve
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Old 12th Dec 2018, 7:45 pm   #26
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Default Re: Hacker Sovereign II RP25B

Hi Steve,

Just to say that my 22mA was from memory, so don't rely on that too much It doesn't sound like yours id far off, but if you're feeling inclined, then the correct procedure is to use the provided link on the amp PCB - check the manual, but from memory that should be 4mA (and don't forget the mid-point voltage adjustment too). It's probably wise to use the set for a bit first, just in case the caps are still slowly waking up, but it sounds like that won't be too much of a chore! You can perhaps now see why Hacker sets have such a following

All the best,

Mark
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Old 12th Dec 2018, 8:05 pm   #27
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Default Re: Hacker Sovereign II RP25B

I admit I'm not the sharpest tool in the box but I have to say I found the Manual rather confusing and hard to relate to the set in front of me. Never mind... I have now aligned the AM RFs (and checked the FM too) and the scale calibration, alignment and tracking are all now pretty good. The strange thing is why these were so far out before... there are no obvious signs of a 'phantom twiddler'.

The only remaining thing is the inter-station muting button, that doesn't work (and I'll never use anyway!). Any short cuts to fixing it?

Steve
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Old 12th Dec 2018, 8:08 pm   #28
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Default Re: Hacker Sovereign II RP25B

They always seem to need an RF line-up, but the IFs are usually pretty stable. I've no idea why...

For the ISM, can I assume that you've had a go at twiddling the pre-set inside, but still no muting taking place?
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Old 12th Dec 2018, 8:51 pm   #29
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Default Re: Hacker Sovereign II RP25B

Yupp, even tho' the thumbwheeled whatsit in question seems to be referred to by two separate names in the Manual.
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Old 12th Dec 2018, 9:06 pm   #30
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Default Re: Hacker Sovereign II RP25B

Yes, I spotted that! I think they forgot to update the text in the manual when they moved from the earlier model to the "B" version.

As I mentioned earlier, I have had this before, and in that instance it was caused by a faulty diode inside L1. I'm not saying that will be cause for your set, but I arrived at it by following the signals, and the same approach will work for you.

The way it works is TR2 is fed with 10.7MHz from pin 9 if the IC. It amplifies it, and the AA119 inside L1 does basic AM detection, providing a DC voltage at pin 6 of the IC that is proportional to the amplitude of the 10.MHz signal. A certain voltage causes the transistor on the right-hand end of the IC to conduct, which removes the signal from pin 8 of the IC.

So there isn't much to check. TR2 is a "Lockfit", and these can fail. But if a 'scope check reveals a healthy 10.7MHz signal on the collector, then it's probably OK. If the DC voltage at pin 6 fails to change when the size of the 10.7MHz signal comes and go, then that might point to the diode, or any of the surrounding resistors perhaps.

Just for fun, I've attached a picture of the insides of L11. From memory, I think that's the replacement diode installed.

Don't forget my offer if you're stuck - I know very little about valves, but love a good transistor set
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Old 12th Dec 2018, 9:21 pm   #31
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Default Re: Hacker Sovereign II RP25B

Thanks twice over, Mark. That's really helpful... something for me to get dug into tomorrow. I'll look forward to it. Not been feeling so well today what with one thing and another.

Steve
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Old 13th Dec 2018, 11:54 am   #32
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Well, I sat down this morning and acquainted myself in depth with Mark's excellent exposition. I thought I would first check the basics, and took a peek at the pushbutton selector switch connections.

This is what I saw: one of the tags had been left unsoldered. It looked intentional. Anyway I couldn't see any harm resulting from soldering it, so that is what I did.

Switched on, selected VHF/FM, and tuned between stations. Not much difference. Then I tried adjusting PR1, and it worked! The interstation muting now works correctly and can be selected and deselected. Rather a classy feature actually... in keeping with the rest of the set.

So I now have a completely working RP25B, with all luxury features. I shall now put it back together. Just one minor thing... has anyone got a spare trim for the handle that's missing on my set? This doesn't bug me unduly, since the bare handle looks quite nice as-is, but I thought I'd take the opportunity to ask.

Steve
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Old 13th Dec 2018, 1:29 pm   #33
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Default Re: Hacker Sovereign II RP25B

That's excellent news - always worth a thorough visual inspection before reaching for the test gear, especially with hand-made gear. I remember finding an unsoldered joint on the pilot lamp holder of a Hacker Mayflower many years ago - it did actually work because it had been tightly twisted

Those handle trims are notoriously difficult to find - they just fall off so very easily. I'm short of them myself. Fingers crossed
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Old 13th Dec 2018, 6:27 pm   #34
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Default Re: Hacker Sovereign II RP25B

Forgive my ignorance but isn't the handle trim strip simply a length of leatherette held in place (or not) by impact adhesive? If so such material is readily available from on-line suppliers in sheet form and in a range of colours. A replacement strip could easily be cut to size with a sharp craft knife and fixed with impact adhesive or even double sided carpet tape. Just a thought.

Alan
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Old 13th Dec 2018, 6:46 pm   #35
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Default Re: Hacker Sovereign II RP25B

Handle trim.
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Old 13th Dec 2018, 6:48 pm   #36
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Default Re: Hacker Sovereign II RP25B

Ah, the metal clip at the end. Could fashion a couple of those from aluminium sheet and then polish to a shiny finish.

Alan
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Old 13th Dec 2018, 6:53 pm   #37
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Default Re: Hacker Sovereign II RP25B

This 'lack' is no big deal for me. I may even prefer the look of it without the leatherette.

I must go back and look again at the circuitry of the inter-station muting feature. It seems to act as an a.f.c. too...


Steve

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Old 13th Dec 2018, 8:03 pm   #38
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Apologies - I somehow missed the picture in post #18. Having just seen it, I see that you're missing the Rexine strip from the handle, as well as the chromed covers at the end.

It looks like someone has taken the time to clean up the remains of the double-sided tape that holds the Rexine in place. Until that's been done, they generally look pretty horrible. Once taken back to the bare aluminium, they look pretty nice. Some of the other sets stuck with bare metal.

Not needed in this case, but my usual tip for removing the glue and tape from the handle is simple: leave it submerged in water overnight. It practically falls off with almost no effort afterwards. Saves a lot of effort and chemicals

I've seen lots of attempts to substitute the lost Rexine, but they always look different to the set - even though they might look pretty nice in their own right. To that end, I removed the Rexine from a scrap cabinet - the piece that covers the bottom and side panels can yield enough for 2 handles if you're lucky. Since doing that, I still haven't worked out the best way to perfectly cut the Rexine, as any errors will be very visible on the handle. I guess it'll be a case of using brand new razor blades and a good steel ruler, but I keep thinking that there must be a more scientific method. Perhaps even two razor blades separated by a block of wood to ensure the width of the strip remains constant?

Anyway, if anyone has a scrap cabinet, that might be the best source. It doesn't have to be the same model, of course.
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Old 13th Dec 2018, 8:03 pm   #39
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Default Re: Hacker Sovereign II RP25B

Quote:
Originally Posted by Panrock View Post
I must go back and look again at the circuitry of the inter-station muting feature. It seems to act as an a.f.c. too...
Yes, that is correct. They thought of everything
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Old 13th Dec 2018, 8:45 pm   #40
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Default Re: Hacker Sovereign II RP25B

I'm enjoying using this new Christmas present to myself now. It replaces a Grundig Concert Boy that I left behind at the Bring & Buy. Definitely a step up I think...

Mine is a dark grey example - very distinguished. I've sparingly applied a little vinyl dressing to bring out the beauty of the finish. I understand they were available in dark blue too? Other muted colours might also look nice.

You can tell Mark's enthusiasm for the marque (hey, is that a pun?) is beginning to rub off on me.

Steve
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