Marconi CR100 - £30 bargain

[G6Tanuki]

Anything will do: to be honest you don't want 'extended frequency response' so the cheaper-the-better!

[HamishBoxer]

Certainly some re stuffing to do, if you go down that route.

[Bazz4CQJ]

I re-built my HRO a few years ago. It had not been used for some time and was at least 100% dead.

Taking out one of the original paper caps, it just fell parts in my hands, leaving a great spiral of silver foil. The connecting wires to the carbon rod resistors fell off if you looked a them, and the large electrolytics, on removing them, were light as a feather... and dry as a bone.

Apart from a few silver mica caps, I think that I replaced everything; simple replacements, no re-stuffing. I refered to the task not as a re-build, but as a Mid-Life Update, making quite a few changes, like tearing out the useless (CW-only) crystal filter.

I'd bought the set way back in 1968, and it arrived mostly as originally constructed - just a couple of paper caps replaced, and was in daily use for quite a few years. I wish it could talk and tell me what adventures it had, travelling across the Atlantic, deep in the freezing hold of a Liberty ship while being trailed by U-boats... ping... ping .

B

[dave walsh]

Re the case colour David [post 36*] I've seen them Grey but I do have a [dullish] silver one. It's in the North so I can't comment further except that it might be a "special edition" of some sort as it looks a bit superior. I've wondered if there was some reason why the Navy often painted it's comms equipment in a strong blue shade, other than to ID seagoing equipment perhaps?

Dave W

[HamishBoxer]

Mine that I longed disposed of was Grey. Though I prefer the Navy version in Blue.

[G3PIJpeter]

Originally Posted by Bazz4CQJ

I re-built my HRO a few years ago. ... I refered to the task not as a re-build, but as a Mid-Life Update, making quite a few changes, like tearing out the useless (CW-only) crystal filter.

Sacrilege! The CR100 has the same type of single crystal gate. It gives very sharp single-signal copy for CW. What did you replace it with in your HRO?

I added a refurbished Kokusai mechanical filter to my HRO total rebuild, switched in / out with a relay - so I get CW on the original single crystal and SSB on the mechanical filter and AM with them both switched out.

Peter G3PIJ

[AmateurRepairer]

Would appear that my electrolytic capacitor has had it, completely knackered and when I unscrewed it most of the stuff inside decided to fall out, hope it’s nothing too damaging lol. I promptly hoovered up and ventilated the room, hopefully should be ok. Does anybody know any modern replacements ? I can clean out the original tub and replace the internals. Thanks.

[Bazz4CQJ]

Originally Posted by G3PIJpeter

Sacrilege! What did you replace it with in your HRO? I added a Kokusai mechanical filter to my HRO total rebuild, so I get CW on the original filter and SSB on the new filter and AM with them both switched out. Peter

I have to admit that the replacement for the filter is a... 'work in progress'; impacted by the pandemic! I suspect that something like your Kokusai is hard to find now? I like your approach that you've sought to add "capability" so restoring the HRO to its original status as a communications receiver, not just tinkering with its appearance!

Anyone have good ideas for mods to create a modern filter that would be good for SSB in a CR100 or HRO?


@ Amateur Repairer, replacement of the cap depends on whether or not you want to retain originality inside. If so, you need to buy modern components of similar specs (capacitance and voltage) which are easily obtained (Panasonic components off ebay?), and then "stuff" them inside the old can. If internal appearance does not matter, or just to get you going, just wire in new components.

B

[G3PIJpeter]

Originally Posted by Bazz4CQJ

Anyone have good ideas for mods to create a modern filter that would be good for SSB in a CR100 or HRO?

I wrote an article for issue 33 of the VMARS 'Signal' quarterly publication about adding a mechanical (or ceramic) filter to the HRO. If you don't have a copy and are interested, drop me a PM and I'll send you a pdf of the article.

Peter

[Graham G3ZVT]

Originally Posted by AmateurRepairer

Would appear that my electrolytic capacitor has had it, completely knackered and when I unscrewed it most of the stuff inside decided to fall out, hope it’s nothing too damaging lol. I promptly hoovered up and ventilated the room, hopefully should be ok. Does anybody know any modern replacements ? I can clean out the original tub and replace the internals. Thanks.

That's no problem and the job needs doing anyway.
First thing first, I'm not sure if you have the manual, it's here
CR100 MANUAL
The inside the can is the equivalent of three 8uF 400V electrolytic capacitors, just buy three ordinary wire ended capacitors, with those ratings. You will find there is plenty of room inside the empty can, we call this "restuffing".
These caps are cheap, you will probably get a choice of radial or axial leads, it doesn't matter too much but probably radial would be easiest to mount.

It's no use posting a picture of the hole in the chassis where the can used to be, what we need to see is the state of the old capacitor so we can advice you how to proceed.

[Graham G3ZVT]

PS, as 8uF caps are not a common value any more, I would order one 6.8uF and two 10uF

[AmateurRepairer]

The old capacitor is attached. I simply unscrewed the base so I could degrease the chassis. And the bottom fell out as well as a substantial amount of the stuffing.

I’ll probably have the caps re soldered and put back in by a more competent electrician, I’m terrified at that 400v rating to be honest, does not sound like something you can get wrong and live to tell the tale, unless I am incorrect?

I’ve also finished removing all the things off the front panel, the rocker switch is just going to be cut off with dremel as I can’t seem to get it off.
I’m also going to be stripping the paint soon, then a session with the rattle cans (decided on battleship grey).

I’m also retro fitting a small speaker in the top left hand side of the unit where the old S meter used to be. I’ve got some radio cloth off eBay so I’ll make a fretwork frame to hold it on and use the original screws so it looks like right. I’m also fitting a Bakelite on off switch on the front in the last remaining gap, it looks period correct and ensures safety.

Not one for the purists but I need a useful receiver.

[AmateurRepairer]

Noted Rambo thank you

[turretslug]

I don't think that the contents of old electrolytic capacitors are unduly harmful, but it's wise to minimise skin etc. contact with the innards of anything that long pre-dates the likes of RoHS and so on- some manufacturers may have used "magical potions" additives to improve the performance of their products in some way or another that they kept under their hats and could have involved all sorts of trace nasties. Some folk get quite exercised about old oil-filled capacitors that could include PCBs, but I think it's wise to treat the insides of any type of vintage capacitor as potentially harmful. No-one can specify what degradation reactions have taken place over many decades. Don't panic or lose sleep, just use common sense!

I recall that the original PSU multi-section is a particularly tall unit and the can would comfortably accomodate 3x 10uF 450V units- modern high voltage electrolytics are specified around SMPSU usage and have excellent ripple current and HF characteristics. In my CR100 that I rebuilt long, long ago, the base cap had bulged and ruptured, so I just discarded it and replaced it with a more compact 500V Dubilier unit purchased from the long-defunct HL Smith of Edgeware Road. As it was a tad slimmer, I used the original clip with a strip of aluminium shim. (That's not the original transformer- that had burned out, a common syndrome, I used one from a scrap Sansui receiver back in the good ol' bad ol' days when you could just gather what you fancied at the council tip. Yes, there's a masochistic streak in me that drives me to re-build the basket cases that others walk past).

[AmateurRepairer]

I’m going to scrap the rest out submerged under water in the sink, no risk of Dust then. I only want the shell. That’s what car mechanics do with old drum brakes.

I’m probably going to leave the transformer as it appeared to work when I plugged it in when I first purchased it. I just need to find a suitable replacement bulb holder for the old one which just crumbled away. Any ideas of replacements from eBay etc.

[AmateurRepairer]

Somebody asked for a photo of the soviet stuff, is this a valve or something else?

[Radio Wrangler]

How would I put a proper SSB filter in an HRO, CR100 or AR88?

I might have, back in the sixties, but not now.

I'd keep the set pretty much standard and just enjoy the CR100ishness of it. I'd have another set from the SSB era to use for ssb. Out of choice an RA1772, please. But I'm not expecting to find one at the end of my bed tonight. My RA1217 is quite drive-able and has good crystal filters as well as AGC that works on SSB, but the receiver is too easily overloaded.

In this day and age, keep your eyes open and you'll come across SSB sets, and some at worthwhile prices.

Enjoy your CR100 for what it is. It can show you what things used to be like. Few other sets can do that.

David

[Radio Wrangler]

Originally Posted by AmateurRepairer

Somebody asked for a photo of the soviet stuff, is this a valve or something else?

It's a 'metal valve' as developed in America. The metal can is the envelope, there is vacuum directly inside it. It uses glss bead seals on the wires out to the octal plug base.

Zareaux was a brand name used by the Z and I Aero company of the UK. They imported Soviet valves and marked them up with western numbers and sold them at very attractive prices. They were seen as cheap and cheerful alternatives that would sav you a bit of money, but in reality, the valves might not be perfect equivalents in all cases, but they were good quality.

A lot of AR88 were shipped out to the Russians in WWII, and they are stuffed full of metal valves, so there's no surprise the locals started making that style.

David

[AmateurRepairer]

I’ll probably stick the metal valve back in, if it works. If not I’ll happily keep it as a piece of technology history.

I don’t plan on doing anything non reversible, I just need a useful wireless for now then no doubt when funds allow in the future I’ll put it back to hoe it should be.

When people refer to “silver caps’ do they mean the capacitors in the bottom of the chassis? If so I think they’ll be a nightmare to replace as there are literally tens and tens. Is there anyway of testing them using a multimeter or are they notoriously unreliable to the point of just replace it, lol.

Most caps need replacing as they have leaked anyway.

[AmateurRepairer]

I’m missing the bottom bit with the prongs off the bottom of the can, is this easily remakeable