This "Recent Repair" was kindly contributed by Peter Lawn.
It was one of those spontaneous buys. My father had encouraged my interest in electronics when you could find valve radios and TV's discarded in any country lane and nostalgia now had me looking for a 1930's wireless to restore. Nothing fell into my price range which was not altogether surprising as I had vowed not to 'waste' more than £10 as this was to be my first restoration attempt. I was going to be away for a week's holiday, and had seen a poorly HMV 463 from c1934 on ebay so before I left I popped in a bid of £7.01 just on the off-chance. I returned to find I had won the auction for just £6 and the wireless was quickly in my hands as it was only a short drive away.
I really had very little idea of what I had bought, outwardly it showed serious signs of age, the finish was off in patches, there were chips on the corners, two slits in the speaker cloth and the top was slightly warped. Inside, it looked like someone had lashed a later metal cased power supply to a battery wireless, but, it was using 4V valves and after unscrewing an unlikely panel I found a 1930's rectifier valve buried inside the power unit. Neatly written on the chassis I read "Serviced by ... 1992". This wasn't so long ago, so at least it had been working fairly recently.
Condition as received
What I hadn't considered when romantically considering rekindling my childhood was the filth and dirt involved in wireless restoration. Black soot and dust lay everywhere and what I assume is vaporised wax covered just about every metal component helping to bind the dirt. This was just not what I wanted my restored wireless to look like!
It had been described as 'untested', so I bought the trader service sheet from this site so I could check the main components before I started on the cleanup operation. Although HMV had obviously reworked the 462 battery version to mains operation, I was actually very impressed with the engineering. It only took 4 bolts and a few screw terminals and the main chassis could be pulled. Obvious signs of previous repairs were a couple of wax capacitors hanging from under the chassis and a prominent fluorescent blue Hunts electrolytic. In all I found 6 capacitors and one resistor had been replaced, three were from failures embedded in typical HMV capacitor cans, two were very early Radiospares parts!
Good news was the output transformer and choke assembly were all showing continuity. Bad news, the mains input wasn't. Opened up the power supply and eventually breathed a sigh of relief as it was just the mains switch. A look at the circuit diagram revealed a possible reason why, there were two capacitors from mains to chassis for RF suppression and these were mica originals and could easily have broken down. Which brings me back to the "Serviced by ...". Still, just as well he didn't replace them as the reservoir capacitors were also original, evidently leaking, and could have blown the mains transformer.
Restoring the chassis
Stripping and cleaning the chassis and power supply was a real chore and took several evenings of careful scrubbing with white spirit, soap and toothpaste. There was very little rust as HMV had galvanised the chassis top, plated most parts and over-painted some. The surface was heavily discoloured in places and the plating was off most of the brass frame of the tuning condensor but to my mind this is metal patina. I used naval jelly to remove the few rust spots and to take the surface rust off the worst of the screws. Phosphoric acid based, this leaves a grey oxide finish which looks a little like aged plating. The whole lot was sprayed with WD40 to hopefully provide a little rust protection.
I know there is debate about replacing original capacitors, but I took the view that to leave them puts at risk the main components that are irreplaceable. I therefore chose to renew all except the mica ones but I have kept the few remaining originals and will leave them in the cabinet. The metal boxed and wax block capacitors were extracted from their casings and replacements put inside. Where did Hunts get that glue like wax from? In a moment of madness I did think of reproducing the TCC capacitor sleeves but overcame the urge although I did construct a wax paper box to hide an electrolytic.
The volume control was showing open at full volume so I investigated as it served as a grid bias resistance. There was no wiper, a fixed contact plate pressed down onto the surface of the carbon track to make a contact. This works well for valve designs where resistance in the wiper circuit would have no significant impact. It looked like the track was polluted with flux from the original build so I cleaned it using paper as an abrasive by pulling from under the contact plate under slight pressure.
The tuning dial is cylindrical and a light within the cylinder is projected onto the front through the 'Liquid Light tuning indicator'. This comprises a small coil set into the anode of the IF amplifier which deflects a moving iron plate set directly in the light path causing the beam to be deflected. The translucent dial material on which the scale is printed must have at one time been flexible as there are guide rollers, and although intact, it had badly shrunk, hardened, and the guide rollers had worn away the edge so it no longer fitted properly. Only solution was to recreate the artwork on the PC and print a replacement.
The power supply wiring was not in good shape. The wiring was bound as one, mains, secondaries and output, both cotton/wax and cotton insulated. Some cotton/wax seemed to have aged far worse than others and here the wax had softened and run. There seemed very little insulation remaining given the 1000V between the secondary wires. I chose to replace the mains side with PVC and avoid binding the HT secondary to allow an air gap. For safety reasons I also wired the chassis to earth and put in Y2 rated suppression capacitors.
The speaker open construction had allowed ingress of dust and debris and there were uncomfortable scraping noises when moving the cone. I had several attempts at this and a combination of the hoover on full suction, levering and scraping between the gap with thin acrylic sheet, and realignment using the same acrylic sheet as spacers eventually restored completely free movement.
I joined the parts together, shorted out the frame aerial and switched on, monitoring the HT ready to switch off in emergency but it settled a little below the trader sheet value. It hummed nicely when you touched the pick-up input too. Connected the aerial and tried MW but only a very feint sound, an hour later tracing through the circuit with a scope and I discovered I had missed an audio coupling capacitor! Once fitted all was loud and clear, although a feature of the volume control is even when set to minimum, some sound is still output.
Now the wireless was working I turned my attention to the cabinet. The top and sides were solid wood and had survived reasonably well which left two damaged corners and some loose and missing veneer. I first photographed the HMV legend as I might one day make a waterslide transfer. The trim was easily removed and the old surface stripped. I finished with shellac as this is easily reworked. My repairs are not totally satisfactory but it is a vast improvement.
The valves were not all original. An MKT4 replaced the catkin MPT4, a TDD4 for the MHD4 and IW4-350 for the U12. One VMS4B looked like a later replacement, the other had lost the metalised paint which had once hidden a horrendous hole in the azide process silvering which could only have occurred during manufacturing. The MS4B had a loose base so I used the acetone and nail varnish fix.
I decided to investigate the low HT as the MKT4 was not a direct equivalent and went in search of datasheets on http://www.mif.pg.gda.pl/homepages/frank/vs.html finding the MPT4 but only the equivalent AC/PEN. The MKT4 was showing 41mA/9.8W which is above the worst case trader sheet value and well above the datasheet maximum of 32mA/8W. The grid was OK at -10.5V so that left the screen grid. The SG feed measured low at 3K5 instead of 5K but in the end it took 10K to get the MKT4 properly under control. A CD through the phono input now sounded almost Hi-Fi, a little distortion on the highs perhaps.
The fluid light indicator is still fairly ineffective and there is a bit too much gain on local stations despite strong voltage swings on the AGC, but I would want to realign the wireless before investigation. I have a scope but need a signal generator and almost bought an AVO AWO on ebay for £1 before it dawned on me that I would need another SG to check the AVO calibration!
Overall, I would recommend the 463. Although not the most stylish of radios of the 30's, it was at the quality end of the market and this is reflected in the construction, design and performance. A transportable, it is unusually compact for an HMV and is almost wife friendly. The final product is an attractive piece of early wireless history which is very selective and produces a surprisingly good quality powerful sound, a far cry from the popular image set 5-10 years later of the family huddled around a crackly wireless trying to make out the wartime announcements!
Will I restore another wireless? Maybe, if I can find the
time, but the next one will either have to come ready cleaned or it may just
go straight into the dishwasher!
Text Copyright © 2005 Peter Lawn