MF/HF Receiver type R/75/WRDV/3550
 

Following a radio swap this week I now have another unknown comms receiver to investigate. First question is to identify the manufacturer, and it looks like a Plessey to me. The name plate shows the year of manufacture as 1963, which is just as well since there's nothing else to go on. I am assuming that the last line on the nameplate is the type number.

First thing to note is the interesting frequency coverage, 55 to 31,000kHz continuous. This would have to be dual conversion on the HF ranges, and I suspect that a couple of the larger pentodes are the conversion oscillators, but I do not recognise the CV numbers. Radiomuseum can help with CV4007 = 6AL5W and another online table shows CV4015 = 6065 but what are CV4016, CV4055 and CV4058 ?

The tuning gang has 4 sections mounted on a ceramic shaft but there are two different sizes, as might be appropriate for better bandspread on HF. I shall have to power it up to ascertain the 1st IF but there is a 460kHz crystal filter for the 2nd

Other points to Plessey manufacture are the only external power and output connections being made through a Plessey connector on the front panel (apart form aerial and phones) and Plessey metal cased capacitors throughout

The tagstrips are mounted on black phenolic rods, which again may point to a particular manufacturer. The knob construction is superb, no grub screws or collets to seize up, just a phenolic stopper with a shilling-piece slot which releases the knob from a curious flanged carrier clamped to the shaft.

What is the antenna connector type?

Re: MF/HF Receiver type R/75/WRDV/3550
 

Looks like a Rees Mace:

https://www.radiomuseum.org/r/rees_m...169br_216.html

?

Lawrence.

Re: MF/HF Receiver type R/75/WRDV/3550
 

Yes it's a Rees Mace 619 I had one with the power supply .

Re: MF/HF Receiver type R/75/WRDV/3550
 

Wow! There's even a schematic there :)

Re: MF/HF Receiver type R/75/WRDV/3550
 

The antenna connector is what was universally known as a "burndept connector", used extensively on professional and some military gear [e.g. the British "Larkspur" series] for a couple of decades post-WWII.

There were right-angled and straight cable-plugs available, with a range of different-sized cable-entries to suit different coax-thicknesses.

See here: https://harc.org.uk/?page=technical&sub=connectors and scroll down about half-way.

Now extinct on the new market; secondhand ones sometimes turn up at radio-rallies [look in the boxes-of-tangled-cables most sellers seem to have under their benches]

Re: MF/HF Receiver type R/75/WRDV/3550
 

In answer to my earlier question about CV valve types, cruisinradio tells me that CV4055 is 6132 and CV4058 is M8080

Another interesting feature of the construction is the tuning lock lever, which confirms it being intended for a marine environment. I still haven't worked out the 1st IF or the 2nd conversion osc, but I presume that's a little bandstop filter at the aerial input to the tuning circuits which will reject the 1st IF

There is a crystal unit, unfortunately with no xtal on mine, but it seems to provide a single crystal channel which would have to be tuned manually by the bandswitch and tuning control

I think the tagstrips are rather cute but I hope they will withstand careful component replacements

Does anyone have a picture of the associated PSU?

Re: MF/HF Receiver type R/75/WRDV/3550
 

The crystal was typically one which would put the receiver reliably on 2182KHz, the old international marine-distress frequency, which a vessel's radio-ops were encouraged to monitor when not actually handling traffic.

From some of your pics I see the presence of "Metalmite" capacitors - these and their "Metalpack" brethren are really just waxies-in-a-shiny-can and suffer the same inevitable leakage after a few decades.

Re: MF/HF Receiver type R/75/WRDV/3550
 

So far as I can make out, the filter L9 (FL1) in the antenna circuit is for the 2nd IF and the filter L19 (FL2) for the 1st IF is between the the RF amp and the 1st mixer.

A book of words about the preliminary technical information is in the link below, includes alignment info, schematics etc:

http://www.vmarsmanuals.co.uk/archiv...nformation.pdf

Lawrence.

Re: MF/HF Receiver type R/75/WRDV/3550
 

The tuning gang is constructed as a 4-gang, but the two wider-spaced sections are strapped in parallel to form the oscillator section, reminiscent of the way that the R1155 and TCS12 etc. use a wider-spaced oscillator gang to help improve stability. One point of interest (OK, to me anyway....) is the way that the whole of the earthy side of the aerial input circuitry up to the 6BA6 RF stage grid is carefully isolated from the main chassis, only connected at a single point to reduce circulating currents that could increase oscillator radiation. The aerial coilbox sits on several (hidden) Paxolin bushes and strips, the rear section of the bandswitch shaft is also made of Paxolin with a clamp coupling to the conventional steel mixer/oscillator front section and the ceramic gang capacitor shaft completes the isolation. There's even an anti-circulating-current slot stamped into the chassis below the aerial section of the tuning gang and the other two. In these respects, it's reminiscent of the pioneering Scott SLR (Scott Low Radiation) receivers of WW2, also intended for ship-board use with the need for minimal oscillator radiation.

I found a suitable 6400kHz crystal in a rummage box at a rally, just for the sake of 5MHz time-signal reception. It must have one of the nicest tuning drives on commonly-seen receivers, light, smooth and precise with no clever-dick bevel gears or worm drives in the way to wear and cause lash and, unlike the AR88, they bothered to fit a positive end-stop mechanism.

The wiring loom is lovely neat stuff but being early single-strand PVC stuff is horribly prone to shrink-back with the (inevitable) capacitor replacement, I used a small croc-clip loaded with damp blotting-paper clipped to the wire insulation immediately adjacent to each terminal spine before applying the iron- time-consuming but it worked better thanI expected.

Re: MF/HF Receiver type R/75/WRDV/3550
 

What a lovely set, well worth getting going and put into use.

Re: MF/HF Receiver type R/75/WRDV/3550
 

CV4055 is the trusty EL821/6CH6, a small power pentode used by the barrow-load in video-distribution and similar applications, broadly comparable to the ee-el eightyfour. (Don't take that too literally, different pin-out and bias requirement). CV4058 is the good ol' EC90/6C4 triode, CV4015 the EF92 vari-mu signal pentode. One of the appealing things about this neat little radio is the commonality of the valve types, perhaps with the exception of the CV395, a bit like a B8B version of the IO VR150 with ignition electrode.

Re: MF/HF Receiver type R/75/WRDV/3550
 

If I remember right, it was also known as the Pye CAT. There was also a near equivalent from Murphy known as the CAS. The CAS and CAT radios were naval HF/MF equipment for small ships and as emergency reserves for bigger ones. They came with matching MF and HF transmitters, and were usually mounted as a stack of three items, plus a separate power unit which also contained a vacuum relay (!) for high speed TX/RX switching. TX output was about 40W.

Much more info in Electronic Engineering magazine June 1954 page 272. This article was written by one J.R. Humphries of Pye.

Re: MF/HF Receiver type R/75/WRDV/3550
 

Thanks for all the observations and additional information - a full instruction manual even!
It is most interesting to learn about the low-radiation design and mechanical implementation, of which I would have been unaware. I had noticed similar isolation of chassis parts on the Vega 22 which I have enjoyed investigating

Re: MF/HF Receiver type R/75/WRDV/3550
 

As Granitehill says, it is a CAT receiver made by Pye (who took over Rees Mace) as part of the 619/CAT emergency rig on naval vessels. There is also a Murphy version (618/CAS) which I believe was built to the same spec but is much "clunkier", akin to the B40.
I have the 619/CAT system operational, having obtained it from the HMS Collingwood museum in Gosport (sadly now threatened with closure). I declined the PSU on weight grounds and built my own, much lighter, version. Nice receiver, albeit a bit noisy. You can see details of my restoration at http://www.tibblestone.com/oldradios...0and%20CAT.htm