Marconi CR100 - £30 bargain

[AmateurRepairer]

Just bought this old lump for £30 off eBay.

I know it’s an ex navy unit. Can anyone give me any info on it as to what it actually does I know it’s a receiver so does that mean I can tune in to normal LW MW SW stuff? Apologies for the obvious questions I’m new to the hobby.

Thanks

[G6Tanuki]

Yes. it's a LF/MF/HF receiver - from the photo yours has been 'got-at' - the front panel's been reworked with Dymo-labels and an alien S-meter has been added.

Sensitively-restored they can be really good receivers on medium-Wave and the lower-short-wave bands, but don't expect too much in the way of image-reception or tune-to-a-SSB-station-and-expect-it-to-be-stable above 15MHz.

[HamishBoxer]

This covers 60 Khz to 30 mhz depending on the variant,a reasonable communications receiver.That I believe is what the CR stands for.Made by Marconi.

[Ed_Dinning]

Plenty of info and circuits on the web.
They were extensively discussed in Radio Bygones magazine a few years ago

Ed

[M0FYA Andy]

Look out for perished rubber insulation on the wiring, they are famous for it.

[Jon_G4MDC]

I think mine was bought for about that price in about 1973 or 4.
They usually cost rather more than that now in real terms - you have done well.

I did some work on it (with very little knowledge at age 13 or so) and I'm still here to talk about it.

The construction seems scary to me today, almost 45 years on. Good luck with it.

I love the buy now get the specs. later approach, you have to get it going now! A more than half decent set, I await the final result.

[majoconz]

I sailed on a WW2 Liberty ship the "Glaisdale" in the 60's - with a CR100 as the low frequency receiver and an Ellectra for the HF bands. One trip from Cardiff to Halifax NS and back to Liverpool then up to the Clyde - the ship went in to dry dock and I did a couple of relieving trips up and down the coast when suddenly I was back to the Glaisdale! BUT she now had an Atalanta which covered everything from 15kHz to 30MHz and an Alert as a 500kHz watchkeeper - deaf as a post as usual. Don't remember much about the CR100 so it couldn't have been that bad! Bit short on selectivity maybe - plenty of signal strength on the North Atlantic so sensitivity not a problem.

[Jon_G4MDC]

Doesn't one valve have the top cap anode when the rest are grids?
I seem to remember finding that out the hard way!

[David Simpson]

As well as enthusiastic members on this Forum, you'll no doubt also get help & encouragement on the VMARS Forum, and the "Ship's Nostalgia - Radio Room" Forum. Your Rx is a pucka gen vintage radio restoration project.

Regards, David

[AmateurRepairer]

Thanks all for your response. I plan on returning her to 1945 spec if possible

[HamishBoxer]

That sounds a great plan.

[llama]

I think the Navy version was called B28. In fact I think the "CR100" I have in the out-building is actually a B28. So maybe CR100 was the designation for commercial or Army use. Now I've said this an actual expert should be along in a minute to confirm one way or the other!
Graham

[Graham G3ZVT]

That is indeed a bargain, and most of the liberties that have been taken with it look like they can be reversed reasonably easily.

The S meter addition was such a commonly done thing, you almost expect to see it, it looks "in keeping" and I have no problem that it's there. If anything, it's the red illuminated power switch that I wish wasn't!

It's the /4 naval variant, there was a socket where the S meter is now and a control knob where that metal toggle switch is, both were for
a Radar Interference Suppressor function.


So what you have there is a "General Coverage" LW/MW/SW/VLF receiver (excuse the mixed units).

I look forward to a successful restoration.

[dave walsh]

You will find loads of info re these on line [at least one complete re-build] AR plus the info on the Forum. As Ed says the articles in Radio Bygones are very comprehensive showing the four main types and their coverage. The CR100 was quite popular after the War as it was definitely solid, well built and a cheaper, [value for money] alternative to other sets. Like Graham I thought the two designations referred to different armed forces with the Navy getting the B's [often painted blue]. They all look similar but I was a bit embarrassed when I obtained a B29 VLF set. I had realised that it was mainly good for listening to submarines or the occasional low frequency Beacon but [in those days of limited info-unlike now] it took me a long time to realise that it was a TRF and not a Superhet like the others!

Dave

I think it was disputed [but confirmed later in Radio Bygones] that there was a [very rare] small "add on" TX to the CR100 that went on top!

[Dave757]

Originally Posted by dave walsh

Dave

I think it was disputed [but confirmed later in Radio Bygones] that there was a [very rare] small "add on" TX to the CR100 that went on top!

Hi Dave,

Yes there was definitely such a transmitter, but it was not made by Marconi.
I had a brand new one, still sealed in the original plastic bag.They didn't
sit on top of the CR100,- being just an open chassis, they were designed
to be attached to the underside of the lid.
I understand they were issued to ACF units.

Kind regards
Dave G0ELJ

[AmateurRepairer]

I plan on dropping the chassis tommorow and doing a full inspection. I’ve got it home, does anyone know why soviet valves are in it

Was this commonplace? Also I appear to need to open one of the dials as it is all full of muck, but it is sealed. Do I take the dremel to it and lightly and carefully split the front then re seal using black silicone or similar product?

I have a friend who is willing to shotblast the cabinet once I’ve got it stripped and another who’s willing to repaint it back to Marconi colours as it should be.

With regards to any additions that have been added, I intend on removing them, as whoever has done this to this poor radio has made a hash of a job, worst wiring I’ve ever seen.

[AmateurRepairer]

Oh hell, pardon the french, what have I just done here, just pulled this thinking it was a valve. Have I FUBARD it or can it be fixed?

[Uncle Bulgaria]

I'm not at all aware of the innards of that receiver, but from here that looks like a valve with a top cap that you've pulled out of its base. Don't pull them by the glass envelope if there's a base to grasp is a lesson I'm sure you've learnt! If it's got some alphanumeric code on the glass you can work out what it is from one of the online valve databases, or discover it's some other similar-looking component and whether you can get another one.

As far as the dial goes, I'd say don't touch the Dremel. I always assume someone put something together, so it can come apart again. The advantage of old things is that often this is the case, whereas with modern (especially cheap) equipment there are methods like ultrasonic welding which can only be broken apart, often damaging something else, worse luck.

As you get more experienced, you'll get to know tricks that are commonly used for fixings, and how similar parts come to pieces. I can certainly say to be very careful with parts that show on the outside, because if it goes west you'll kick yourself you didn't do a better job each time you look at it...

I expect as you strip it down and more fixings become visible it will become clear how parts come apart what needs to be cleaned and how to go about it. Be gentle and methodical, as labels and dial legends can rub off!

Take numerous photographs, or better make sketches so you know what goes where - I find as I draw something it goes in, whereas a photograph can be very unclear a few weeks later. I make diagrams with screw types and lengths, as when they're all in a pile it is a nightmare trying to work out which one goes where, and valve equipment is usually held together with a lot of similar-looking screws. Often there are some that are a specific length or type for a specific purpose that may not become clear until you've taken something else out.

[AmateurRepairer]

Is this what my set should look like, If so I’m more than willing to swap the S meter with someone who needs it in return for the missing parts I need, if anybody would like and has spares lying around?