c. 1947 Mullard MUS221 AC/DC MW/LW/SW 5 valve table radio

[howard]

Hello again,

I've been busy doing other things lately but I have managed to restore this post-war Mullard MUS221 bakelite set which I acquired from a table at the Wootton Bassett event a few weeks back. It had obviously been stored in a loft for many years as its case was dull and inside it was rusty and dusty but I thought I'd have a go at getting it to work again and looking nice. This model is a clone of the Philips 371U in a different (and IMHO not quite so nice) cabinet with a square dial and vertical bars over the loudspeaker grille but its chassis is identical. I had high hopes for this set as it hadn't been got at, and I already have a Philips 371U which works very well (and better than my 371A which tends to hum) and I wasn't disappointed. Cosmetically its cabinet was in need of TLC but it had no cracks or chips, just a couple of minor scratches on the front, the grille cloth had shrunk leaving a gap one side and the coachline paint was peeling off. Internally some wiring needed resheathing, its EF39 had lost most of its metallisation and it still had all 18 of its original tubular capacitors including three 1000v US made Spragues, but both 32uF screw mount smoothing capacitors had been replaced in the distant past, as had its switched volume potentiometer and its EBC33 (with a Marconi W147). The Mullard service manual for the MUS221 is available here ....

http://www.service-data.com/section.php/5052/1

Before switching it on, its audio coupling capacitor and mains lead and straps were replaced. It then just about worked with a lot of whistling (which was improved by replacing the peeling EF39 with a NOS Mullard obtained from the Dunstable Downs event for £1) but obviously all its tubular capacitors needed to be replaced ... and then the dial cord snapped so that ended its initial test. The chassis was removed from the cabinet and cleaned with Rustins rust remover and white spirit, the on/off switch, waveband switch, volume potentiometer valve bases cleaned with DeoxiT, all its black and wax tubular capacitors were replaced with 630 volt polyesters and the wiring to the loudspeaker, dial lamp and around the dropper was resheathed and the dial cord replaced. Also cleaned was the switch in the aerial socket, a piece of card soaked in Deoxit was rubbed between its contacts which are accessible underneath. The set was retried and now it was working quite well on all bands. An interesting repair was found to have been performed on the switched volume potentiometer, a new switched pot had been fitted with the end of the original spindle very tidily spliced onto the new one, the original open switch had been replaced back on the front and the switch on the back of the new pot left disconnected. I then took the set over to Ron Bryan to check over.

The set was switched on and left to warm up for a good half an hour and when turned over I noticed liquid had leaked from a tubular high voltage 8uF electrolytic capacitor under the chassis and as it was getting extremely hot the set was quickly switched off ! That was disconnected and a new 450v 8uF was tacked in place. The HT and valve voltages were found to be OK as were all the critical resistors, but I had noticed that the AGC hadn't been working correctly on the local radio station and indeed one resistor in the circuit was found to have climbed some 50% in value. I then took the set back home to finish it off, the AGC resistor and remaining Sprague capacitors were replaced and the new 8uF electrolytic stuffed into the original can (dated January 1945).

The cabinet was completed dismantled including removal of the loudspeaker baffle and the dial glass and the inside and outside were cleaned with upholstery cleaner and a toothbrush. All the flaking paint in the coachline was removed with Nitromors and the whole outer case wiped down with white spirit. The cloth was removed from the baffle, and stuck back so that the stretched piece along the edge would be hidden by the cabinet. The glass and dial were gently cleaned and the foil frame aerial inside the cabinet cleaned gently with Brasso. One of the metal chassis brackets was rusty so that was cleaned up with Rustins rust remover. The coachline was then repainted with two coats of beige acrylic paint, each time smoothed down by running my thumb over the channel and when dry the excess paint cleaned off with a damp cloth and thumbnail. The two scratches in the front were touched in with shellac, left to dry overnight and then the cabinet was polished all over with Brasso followed by Beeswax in Turpentine. The dial pointer was carefully adjusted ready for realignment, the set reassembled and taken round to Ron for realignment.

With this set it's important that the switch contacts in the aerial socket are clean and that the correct sized plug is used in the socket to disconnect the plate aerial and to connect the signal generator via a dummy aerial to the aerial coil circuit. The IF was checked first and it was found to be spot on at 470kHz. The IF trap likewise was OK. There are three adjustments on each of the MW and LW bands, adjustment of the oscillator coil (good robust coils with brass screws, unlike those in later Philips sets) at the low frequency ends of the bands, wire trimmer capacitors at the high frequency ends, and adjustment of Philips aerial coil trimmer capacitors. On SW there is no aerial coil adjustment. Once the coils and trimmers were correctly identified, MW and LW peaked up really well, previously there had been a lack of gain at the high frequency end of the MW band. Fortunately all the wire trimmer capacitors were still spot on so there was no need to unwind or add on any bits of wire. SW was found to be more or less spot on so was left asis.

This Mullard MUS221 is an attractive looking compact radio and works very well now on all bands with good sensitivity especially when used with an external wire aerial, and it sounds good with plenty of volume. It readily picks up RTE on LW and in the evening comes alive right across the SW band. Cosmetically it has come up very nice too.

My thanks to Ron for his help restoring this set.

Howard

[ms660]

First class job Howard, nicely done, excellent descriptive write up as well (always important)

Good look with the next one.

Lawrence.

[neil29]

It is a nice radio Howard. and as usual you have done an excellent job. ive got some radios here if you fancy having a go restoring them . cheers neil.

[Andy - G8MNM]

As ever, Howard, you always do a wonderful job on your restorations.
And for getting an EF39 NOS equivalent for a quid well done!

Regards

Andy

[Tim]

Fab job Howard. What a handsome set.

[greasylox]

A very tidy job, well done, a nice looking set it is too.

[howard]

Thanks all,

It's surprising how well this Mullard and the Philips 371U work, they really are good and are good looking sets. The biggest problem I had restoring the case on this one was getting a shine on the areas between the ribs along the top front.

Howard

[Hybrid tellies]

Nice set, great write up as well.