Marconi CR100 - £30 bargain

[AmateurRepairer]

Forgot to attach image. Doh.

[G6Tanuki]

Originally Posted by AmateurRepairer

Forgot to attach image. Doh.

Lots of horrors there: the metal-canned capacitors are ages-old, bound to be leaky-as-a-sieve and need to be replaced; you've also got a few-days-of-toil replacing the brown rubber-covered wires that are prominent in that shot.

[the capacitor in the bottom-left-corner of the photo - the one in the dull silver case with red printing _might_ just be a US "Sprague" paper-in-oil part, which tend to survive better without becoming criminally-leaky]

[AmateurRepairer]

I replaced the wire from the cap to the other bit using some standard 12v car cable, not the tidiest I appreciate but it will work, no rworries Aston why it won’t. I’m attaching some better quality photos in better light. I’ve got maybe 2 weeks of re wiring to do to replace the rubber perished stuff.

[AmateurRepairer]

First batch of images

[AmateurRepairer]

Second batch of images

[AmateurRepairer]

I’m beginning to think this is going to be a bit much for me to be honest.

[AmateurRepairer]

I’ve decided to keep it on, taking out the middle but under the meshing bit, I’ll re wire what I can but not sure if I’ll have it done this time next year.

[AmateurRepairer]

I’ve undone the shaft that goes down the middle of the middle section, but I’m struggling to pull it. Anybody got any experience.

[turretslug]

Whatever you do, do it gently!- the wafer switches can be delicate and replacement is one of the more tedious tasks in any electronic device. With the shaft probably having been in place for the best part of 80 years, it's little surprise that it gets a bit stuck, especially with the stiction of the 8 wafer slots, the Paxolin may well have swollen a little. Make sure that the coupling screws are thoroughly undone, as the shaft will have quite deep screw recesses in it. To help ease the switch, note that each coil-box has a steel switch mounting bracket between its two wafers- try rocking this bracket fore-and-aft a little, you should see the shaft sliding fractionally along the switch inner. Once there is reasonably free movement in all four sections, try gripping the switch shaft at right angles with pliers somewhere along its length where you can exert leverage against a coil-box screen- this will limit travel if something slips. Be very wary of gripping the end of the shaft through the hole in the rear panel with stout needle-nose pliers and tugging as this could destroy the whole switch-bank if it suddenly moves. At all times, be careful that the shaft doesn't bind on one of the switch inners when the other seven seem to be sliding along.

When I overhauled mine, I thoroughly cleaned and polished the shaft once it was out and drilled a small hole in the far end, tying a string through it so that I could wrap it round a screw-driver blade at the back of the set and incrementally winch it out, so to speak, if I ever needed to take it out again. The good thing is that once the shaft is out, the individual coil-boxes can be disconnected, then unscrewed from the two long mounting rails, making access to them and the RF valve sockets far easier.

Good luck with it.

[dave walsh]

Keep going AR but you really need to focus on the experienced advice . As I said, there is no end to the help here but maybe no end of questions? If you are struggling with organisation or the written stuff, please let us know as you need to keep safe! Your attention to detail is admirable but not every time perhaps? [Others may disagree]. Of course, enthusiastic new members are always welcome [in the right context]. TS said to be careful with the switch but the valve fell apart! You said that you were ready to give up [at post 86*] but now you are seeming to reframe that as just looking at the options [again]

Dave

[AmateurRepairer]

I’m confident I can get it out with the advice turretslug has provided, many thanks.

Update on the front panel, as it’s made of steel a friend in the metal work trade is going to make me a metal blanking plate and tack weld it me into place after I’ve stripped the paint and horrible glue mess off. I’m also ordering some battleship grey rattle can paint to finish it with, some loctite to fix the plastic dial surrounds and some general purpose filler for all I need it for. I’ve looked on Chavfreezone, thanks to all that mentioned it, I’m going to make a new base for all the electrolytics after I manage to gut them. I think he said to make them from Tufnol discs, I’ll drop him an email if he has one.

I am an indecisive man Dave Walsh, I have a plan as written above and I’m ****** sticking to it lol.

[AmateurRepairer]

Followed your advice turretslug, and used a little WD40 and she slid out like a glove. I owe you a pint if I ever meet you lol.

What do I need to do with these coil packs to refurbish them, they don’t appear to have weetabix wires, unlike the rest of the ****** thing.

[AmateurRepairer]

Coil packs all out. Just noticed this nasty burn and rust, anyone know how this might have happened?

[Top Cap]

I have rebuilt several, mainly for Sea Cadets where function and safety were the main things concentrated on. Here's the story of one that was headed for scrap!
http://www.g4cnh.com/public/CR100_Reno_notes.pdf

[AmateurRepairer]

I’m stripping the chassis right down as we speak, I’m having it shotblasted as well as the cabinet. Renewing all wiring, electrolytic capacitors, resistors, some fixings and refinishing the front panel.

[AmateurRepairer]

Looks like someone put new capacitors underneath the chassis and removed the wires to the mounted one, due to be reinstated as soon as I can get this sodding alumini7m out the cap.

[AmateurRepairer]

Started stripping out all the horrible red and mustard weetabix wiring, to be replaced with modern pvc single core copper stuff that won’t rot. At least not as long as I’m around. In the process of ordering some capacitors to restuff the old cans with.

[turretslug]

Is that the aluminium foil sandwich stuck inside the old can as a mass? It might come down to being fairly brutal and using a drill to shred the innards up and shake it out bit by bit. I was interested to read through Top Cap's link above, I'd certainly concur with it being a good guide as to overhaul. It might seem to be a bit of a drastic move to remove bandswitch shaft, coilboxes etc. but it makes it so much easier to work on the chassis- not to mention making it somewhat lighter to keep positioning. Perhaps overhauling a CR100 could be summed up by "Each step is straightforward, but there's a lot of them...." Maybe there ought to be a "sticky" at the top of this forum section to the effect that if contemplating acquiring a CR100, prepare for a near-inevitable square-one rebuild! The wiring deterioration is the one big bugbear as things like leaky capacitors can be replaced steadily and progressively but wiring with crumbled insulation is in a different league of hazard.

Inside the coilboxes are decoupling capacitors for anode and grid circuits- these will need repacing but at least the four-sided screen can be unscrewed to make things quite easy to access. A hefty soldering iron is useful here when soldering connections to the base-plate. The oscillator box anode decoupling capacitor is a low 500pF- this serves to stifle its enthusiasm on the lower frequency bands where dynamic resistance is higher and squegging or excessive distortion (harmonics) could result, the decouplers in the other boxes are the "usual" 100nF (0.1uF). The other 0.1uF decouplers around the chassis have a certain neat appeal in their studded aluminium cylinders and were among the better types at the time, but will still be more or less (electrically) leaky.

Rather than getting bogged down trying to do a marathon session of the rebuild, my approach was to do a chunk every now when time was handy and then and take a break, I can't quite remember but I probably rebuilt mine over a couple of months- heater runs and PSU corner one time, IF strip another, AF amp tagboard another, coilbox cap-change and polish-up- that sort of thing. It's worth it in the end, and the straightforward tag strip layout and International Octal valve sockets contribute to it being easier to rewire than many other sets.

Keep us posted, there's plenty of interest and advice to be had here and I for one think that the CR100 is a useful overall package,

Colin

[AmateurRepairer]

Yes I’m planning on working solid on it everyday until 1st of jan then i will have a weeks break and do something else. I’m probably going to have the coil packs decoupling caps done by my great uncle - he has experience on working on small electronics. I can do most stuff but that may be a bridge too far at this stage.

Yes the aluminium is like a ****** Victoria sponge in there... I’m going to use a mates pillar drill and “Christmas tree” bit then pull out peice by peice as you suggest - a task most dull but necessary! The difficult but will be cutting the new tufnol discs for the bottom of the cans, god help me with that one. Can you suggest any good replacement tags for the bottom, maybe just thin aluminium sheets cut into little squares and bent at 45 degrees? Not sure.

I plan on a full rebuild anyway, everything is coming out and being rebuilt as per should be, then after I’ve had a session with the black and decker with the wire wheel on the chassis I’ll slowly rebuild it, top to bottom like a house. It’ll basically be a new radio, but not a new one if that makes sense.

Any idea where I can get the reproduction labels like the originals or do they not exist?

See attached for poor wiring on this set, glad i didn’t have it plugged in long when first purchased!

[Graham G3ZVT]

From what I could see in your photos A.R. your soldering technique needs some refinement. As well as a big iron you really need some tin-lead solder and some flux paste. If you have been carrying the molten solder to the joint like butter on a knife then you will not do well with this. Hook the wires onto the tag and brush on some flux, then heat the entire would-be joint up so it is hot enough to melt the solder that you apply to the tag, then leave the iron in contact for a second or two, long enough for the solder to flow making a smooth joint.

PS I crossed with your last post.
Regarding making new solder tags for the smoothing caps, do not use aluminium! Try soldering to some and you will realise why.