Hacker RP33 Autocrat

[canonman75]

Hi peeps

Just started on the RP33 Autocrat that turned up in the post today and being unfamiliar with it (I've done much more Roberts than Hacker) I have a few questions.

First, the volume pot has been replaced at some point (with a pot that hasn't had the shaft cut short enough) and I'm just wondering if it's wired up correctly. Please see the photo below. It seems to match up with the circuit diagram in the manual but I wouldn't mind a second opinion please

Second, how do you get the screening can off the smaller PCB? I've taken the screw out of the chassis side and pulled it slightly outwards but the can still won't budge. Is there another fixing that I've missed or is it just a case of pulling the can carefully until it pops off?

I need to get to the AF117's as the radio is dead apart from a background hissing noise from the speaker. If I touch the middle tag of the volume pot with my finger and turn it up and down I can get a humming noise so the amplifier appears to be working okay.

Third, the 'Auto' button seems to have a problem with it's latching mechanism, it doesn't always pop back out again. Is it possible to dismantle the switch bank and cure this? The other buttons are okay.

Thanks in advance.

Cheers,

Dave

[stuboy57]

Yes I have a RP34 Democrat. Yes there is only one screw on the smaller screening for the pcb... it pulls away but can be a bit stiff so be careful, it slides in a groove, if you look at the picture you will see the groove.
The AF117's can be replaced with AF125's which are readily available, but there are loads of threads on the forum about the AF117's
not sure about the switch bank, would need to have a look on mine
The pot looks wired up correctly same as the one I have
hope this helps you but there are far more experienced forum members who can advise

[Radiocruncher]

Hi Dave

I don't have one of these to hand but it does use the same IF board as the Helmsman. Once you have taken the screw out then the can slides downwards. It is a bit stiff so just needs wiggling a bit. The AF117's will almost certainly be causing the failure. I don't have one to hand so can't help with the other questions.

Regards

Graham

[mhennessy]

Squeeze the top/bottom of the can to lessen its grip on the PCB

The volume wiring looks good to me, from what I can see. I assume the wiper (thicker, probably stranded, green wire) goes to the amplifier, while the thinner green wire (solid core) comes from the IF PCB? The power arrangements look OK, too. Being honest, this is probably the best replacement job I've ever seen - whoever did it took a lot of care. I can forgive the shaft being too long - that's easier to fix than the opposite

The switches sometimes play up, but they are the same type that were used by just about every other UK manufacturer. If the latching mechanism is worn, you can replace the whole of the white plastic insert (remove the circlip and spring, the latching pin, and slide it out via the rear. Sometimes you have to remove components from the PCB to allow that) - scrap sets are worth keeping for parts like that. Often it's just debris or a weak spring. It'll be obvious when you get in there...

I have a bit of a soft spot for the RP33. Easy to work on, easy to restore. The cabinet is veneered, so careful with the sandpaper! The front and rear are padded, and if you wish to learn the art of re-padding sets, these are a nice and easy set to start with.

Mark

[canonman75]

Thanks for all the advice so far folks, Mark especially.

I've managed to make some good progress this morning...

The volume pot shaft is now the same height above the chassis as the tuning spindle! it was too long and looked as if it had been chopped short with a big pair of wire cutters rather than cut carefully with a hacksaw. As Mark said, whoever did the replacement did a neat job of the soldering, but they were less than careful cutting the shaft down to size... Unfortunately, the pot is going to have to come back out at some point for a refurb as it's still noisy and Super 10 hasn't cured it.

I've removed all four AF117's and they all s/c to the screens. My trusty Peak Atlas says that one of them is a bi-colour LED(!) and the other three have wildly varying hFE figures. I'm just going to replace all four and have done with it. I don't have any AF127's in stock at the moment so I'm going to try some of those Russian transistors that have been mentioned previously.

Last of all, after removing the button caps (what a struggle that was!) and a bit of point-to-point wiring, I managed to get the switch PCB far enough away from the chassis to attend to the sticking 'Auto' button. With the circlip and spring removed, I managed to pull the shaft just far enough out to clean the latch hole. I would have pulled it out from the bottom but a couple of cans were in the way. Cleaning the shaft, the pin and the gold-coloured flappy bit (I don't know the right name for it) seems to have cured it. Well, 19 times out of 20 it now works, which is a lot better than it was when I started

I will have a go at refoaming the front and back panels eventually. I've never done it before but I have been reading up on how to do it. The only things I'm not sure of, are what sort of glue I should be using and also how thick the foam should be. I think I saw some chap on YouTube use foam from an ironing board cover, so maybe I'll give that a try.

Another thing that's just popped into my head... the knobs on this radio are the smooth black plastic type with a silver insert in the top and no silver skirt. Are they the correct type, and if so, are they meant to have felt washers underneath? Mine haven't!

Sorry for all the questions but I'm still getting to grips with it all

Dave

[mhennessy]

Ah yes, those two cans are rather in the way. It's been a while since I've done one of these...

Regarding the volume control, are you sure C1 on the amplifier board isn't leaking? It sounds like it might be a DC problem.

Those AF117s would almost certainly work after being "zapped", and probably for a decade or more if done properly. I tend to treat ones in Hackers because they are easy to get at; in other, less accessible sets, I replace them. Personal choice - frequently debated

For the foam, I use 3mm scrim foam from here: http://www.woolies-trim.co.uk/p-1562-scrim-foam.aspx

A tip: the waste from the front panel of an RP25 is enough to do the front of an RP33.

I use PVA to stick the Rexine back to the timber. I have a tub that's a bit old now, so already on its way to being set. This means it takes less time to grip during the job.

Yes, the knobs sound OK. Later sets got the same knobs as the RP25/35/37, but the earlier style is more common. I can't remember about felt washers - I'll have a look this evening if I remember.

[canonman75]

Hi Mark

I haven't checked C1 yet but I will do. I've read the article on your website so I've got no excuse!

I'll hang on to the AF117 transistors for further experiments. I've got some of those Russian transistors on order so I'll use those when they turn up.

Thanks for the info on the foam and knobs.

Cheers,

Dave

[canonman75]

Hmmm..... that's interesting.

C1 on my amplifier board is a 68nF ceramic cap. Judging by the soldering, it's been like that since it left the factory. C11 is a higher value than expected as well

It looks like the noisy volume pot isn't a DC issue after all, so I'll have to refurbish it!

[mhennessy]

Yes, that's very interesting

It's quite possible that it was introduced as a change. I'll take a look at my examples to see what they have fitted.

I'm less worried/surprised about C11. For decoupling, the more the merrier

[mhennessy]

Right - just back from the attic!

I have 4 sets, which are 09914, 43867, 45834, 55599.

All but the first one has a 68n capacitor for C1; only 09914 has 2u2. So yes, clearly a change. It's not mentioned in my copy of the manual, nor the versions on Paul's DVD. It's possible that someone somewhere has a supplement that was issued by Hacker...

C11. It's 80uF in the earliest, 160uF for the next 2, and the later one uses a 200uF Japanese type with a grey sleeve (the earlier ones are Philips "blue").

Only the last one uses the Sovereign-style knobs.

No sign of felt under any of them.

HTH,

Mark

[canonman75]

Thanks for the info, Mark. It's very helpful

Nice to know that they never had felt washers under the knobs. That's one less thing I need to worry about!

Just out of interest the serial number on mine starts with 42. I can't remember exactly and it's a bit early to be going up into the loft to go and check!

Dave

[canonman75]

I've made a little bit more progress with the radio today, if you can call it progress!

While waiting for the transistors to arrive, I decided to tackle the noisy volume pot. I've done quite a few before so I went through the usual routine of dismantling it, cleaning the wipers, ring and track with cotton buds and alcohol and lubricating everything with original Vaseline. I also had to clean up the two wipers that come into contact with the ring using a fibreglass pencil, just as Radiocruncher did on the Hunter featured on his YouTube video. To be fair, the tips on the wipers didn't look as bad as they did on his, but they were bad enough!

I checked that it worked okay using a multimeter, then used my signal tracer/injector (a Velleman kit) to check that it would alter the volume of a tone properly. All was looking good, so I put the pot back in the radio and wired it up...

Unfortunately it's still noisy, mainly over the latter half of its travel. If the volume on an RP33 is as loud as it is on a Hunter, then the control will probably never be turned far enough for the noise to be a problem!

I'm sure that the pot is a replacement, as it had the 'RS' logo on the back and its shaft was too long compared to the tuning shaft. Internally, it looked exactly the same as the CTS pot on the Hunter I've just restored, so maybe it was made by CTS for RS Components.

Having discovered that the input cap on the amplifier is a 68nF ceramic and doesn't appear to be leaky, I can't decide whether to take the pot apart and have another go at it (and risk possibly breaking the tabs in the process), source another pot, or just make do with this one.

Any help or suggestions gratefully appreciated

Dave

[mhennessy]

Just about anything wearing an RS logo was made by someone else

To be honest, I'd leave it alone for now - it might be fine in use. Unfortunately, in common with some other AM-only Hackers, there is a DC voltage across the track, so even with a relatively small value capacitor at the amplifier input, there's a chance that noisy operation will eventually return.

I'm not sure why the Hunter suffers from the problem that Graham's video shows, but I've seen in many times - though not in others, as far as I can remember. I usually swap the inner ring and the wipers from other pots with duff carbon tracks or switches - replacing the pot in a Hunter with a modern is much more difficult than the other sets.

[Radiocruncher]

I had a Sovereign RP18 in with an RS volume pot. That was also noisy and was probably the wrong value as it only took a short turn for near maximum volume. I suggested replacing it but the owner decided he would put up with it to keep costs down. It's now driving him mad so will be returning soon for a replacement pot.

Well done on sorting the switch bank out. They can be very fiddly.

Out of interest I have dug a couple of my RP33's out. The older one serial no. 19648 has the aluminium topped knobs. The volume control is not original as it fouls the IF can which someone has 'fixed' by sticking some insulation tape on it. Also it has AF12X series transistors so it's been well and truly got at. It does have a Goodmans speaker though so should sound nice. The newer one, serial no. 52944, looks very different. It has the Sovereign 2 knobs, a thiner aluminium handle which looks like it had a rexine insert at one time. This one is all original with the AF117's still in place and an original volume pot. The speaker is different and unbranded. The case is also a dark rosewood finish so I assume it was available in different colours as the other one is the usual teak colour.

I will have to have a look at these soon as I haven't worked on one before. Good luck with your restoration.

Regards

Graham

[mhennessy]

Probably Lin rather than Log. The value itself won't make all that much difference, within half-sensible limits.

Yes, mine have a range of different handle styles. And as well as teak and rosewood, there is a version with grey/white Rexine covering the case (still black for front and rear). I haven't seen too many of those over the years.

Another difference is that my latest example is made from chipboard rather than ply. But then, only the earlier Sovereign II cases were ply. Most of them are made from a rather horrid particle board that is almost as crude as OSB/Stirling board. It often comes away in big lumps when you try to peel back the Rexine to re-pad the case. But they went back to ply for their later sets, so we can forgive them

[canonman75]

Thanks for the words of encouragement

I started to strip and clean the cabinet last night and it's looking pretty good so far. I've just bought a sacrificial ironing board cover and some more PVA glue so I might have a go at refoaming the front panel tomorrow, if I'm feeling brave enough!

[canonman75]

Time for another progress update...

I decided to re-foam the front panel first, and discovered that alternating between heating the rexine with a hairdryer and spraying IPA under the loose edges helped to get it off fairly easily. After cleaning out the old foam, which was of course nothing but powder, I stuck down the new foam with PVA glue and left it for an hour while I tackled the back door.

The back door was a little bit more difficult, having the extra layer of cloth to take off, but I used the same hairdryer/IPA trick and it all came off without any tearing. I left the plastic grill in place, so had to cut two long pieces of foam to do above and below the grill. plus a couple of small rectangles to do the gaps either side of the grille. After the rexine had been stuck back down I was slightly disappointed to see what you could call 'tramlines' going from side to side, from the edges of the grille, where the pieces of foam meet. Fortunately, after the foam had expanded back to its normal thickness, these 'tramlines' more or less disappeared. Maybe next time I do one of these, I'll remove the grille, cut the foam as one continuous piece (no joins) and refit the grille afterwards.

Once I'd given the whole lot an hour or so for the glue to set, I cleaned up the rexine with Lord Sheraton leather cleaner, which gave it a lovely shine. It also smells really nice, which is a bonus!

For a first attempt, I think it went pretty well. Call it beginner's luck if you like, I do! I would imagine the fact that the corners are straight makes things easier. I bet a VHF Herald would be more difficult with its rounded corners and piping. I'll find out soon enough though, I've just bought one

The next job is to get some Silvo on all the shiny bits and polish up the dial plate with Novus. Hopefully the replacement transistors will have arrived by that point and I can finally get it up and running.

One last point... the only thing I'm not really happy with at the moment is the state of the front grille. It's obviously had a few scratches in the past an has been touched up with paint that isn't quite the same colour as the original paint, so you can see where it's been touched up. Short of masking off the whole grill and repainting it, I'm not sure what to do with it

[canonman75]

Sorry, just thought of another question....

What's the best kind of glue to stick the rexine back on the aluminium handle? I''m guessing something like Evo-Stik impact adhesive?

[mhennessy]

Looks good

You're right; the sets with rounded corners are harder, and it's the corners that show the imperfections. You don't need to remove the Rexine completely - in practice you can leave the top edge and top two corners alone, which helps.

I've not yet re-painted a grille. I imagine that masking it off would be a real pain. But apart from the localised touch-ups you already have, I'm not sure what else is possible, short of scrubbing off all the paint, or painting the whole thing (I've seen both done, and neither is pretty).

For the handle Rexine, I use double-sided tape. That is what was used originally. It took a couple of goes to find a tape that is strong enough - unfortunately I can't remember the exact details, but IIRC it's made by Tesa.

[canonman75]

Cheers Mark

I hadn't thought of just leaving the top edge and corners attached on the VHF Herald. With it being red rexine I guess it's even more noticeable if the corners aren't spot on, isn't it? I had thought about taking the piping off and out of the way to make things easier. I can't see any reason why it wouldn't go back on easily enough.

I'll leave the front grille on the Autocrat for now. If I could get some 1.5mm masking tape and felt brave enough I might have a go but I'll save that for another time!

I'm surprised that it's double sided tape holding the rexine to the handle, the residue looked more like Evo-Stik to me! It came off easy enough though, so I'll get some of the tape you suggested and give it a try.

Ta for the advice

Dave