I bought this set on eBay for about £25.
There are plenty of horror stories about inadequately packed sets damaged or destroyed in transit. Not this time though - it was well packed in a box that previously contained a microwave oven, with lots of bubble-wrap around the set and polystyrene chips between this and the box. The seller used a carrier firm rather than the post, and I had it delivered to work. Consequently it arrived unscathed.
It is not the best example of a Wartime Civilian Set, which explains why the price I paid was so reasonable. The cabinet had been stripped some years ago, and the bare wood was showing some signs of age itself.
Unfortunately the label from the top of
the cabinet was missing, and the plies of the top were coming apart in one place
at the back. The speaker fabric was obviously not original (thin dark-brown
nylon) and was badly damaged.
Internally things were not so bad. The valves were original BVA types. I removed them for testing on my Mullard High Speed valve tester, and all were OK. The mains cable was also original and clearly unsafe.
The manufacture identification code on the chassis was illegible. It looked like at least two and possibly three characters were stamped on top of each other. From the information in the Trader sheet (688) about the modifications in different versions, I think it is probably Ekco (U2), because the mains transformer seems to be the same style as that description.
With the chassis removed it was clear that I was not the first person to repair this set! The original smoothing electrolytics had been removed and replaced with newer wire-ended components hanging by their leads. This was probably done in the mid 1950s judging from the style and date codes on the replacements. I connected my capacitor reformer across the HT, which showed considerable leakage, so I removed the replacement capacitors for individual checking. There was one dual type in a brown tube with black pitch at each end. The pitch had cracked at one end and there were white deposits suggesting that the electrolyte had been leaking. On the reformer this had no leakage, but it also had very little capacitance! The other replacement was a regular aluminium cased type with plastic sleeve. This looked fine but was very leaky and did not improve after 10 minutes on the reformer.
The capacitors are 16uF each and need to be rated at 350V or higher. Since I didn't have the originals or the mounting clip that retained them, I could not fit new capacitors inside the original cases. I therefore decided to use modern axial capacitors of the correct value mounted directly by their leads to the relevant points in the set. The leads could be kept short, giving adequate support for the smaller modern parts. I did not know the ripple rating of the capacitors I had in stock so decided to fit them anyway and check they were running cool once the set had been playing for a while.
I checked the resistance between live and neutral, which confirmed that the transformer and power switch were OK. I then checked insulation between earth and live/neutral with the Megger, which showed considerable leakage. Following the connections through I found a wax-paper capacitor connected between the voltage selector and chassis on the top of the transformer. This was clearly not original, and is not shown on the service data. With this capacitor removed, the insulation test was fine.
At this stage I replaced the mains cable with modern round three-core type, and earthed the chassis. The toggle mains switch is only a single pole type so I connected live (brown) here and neutral (blue) to the transformer.
Sometimes I leave the mains cable replacement until later, but in this case the original was in such a dangerous state that I wasn't even prepared to use it for initial testing.
Initial Tests and Repairs
The wax paper capacitors looked to be in reasonable condition so I decided to try the set with them in place. On the first test the HT came up OK and the set managed to receive a couple of stations very weakly and with some distortion. I temporarily connected an OA90 diode across the Westector, which improved the volume but not the sensitivity or distortion.
The AGC voltage was close to zero, and did not vary as stations were tuned in. The AGC arrangement on this set is somewhat unconventional and I wasn't sure what to expect, but I did expect to see some variation. I temporarily disconnected the AGC decoupling capacitors (C2, C7 and C10) and connected modern replacements. This improved the reception somewhat, but it started to fade away after a few minutes. However this test was sufficient to prove that the wax-paper capacitors which in this case looked fine, was actually as bad as usual, so I replaced them all.
On the next test the reception was improved, but still far from right. The fading out problem still remained too. By this stage there was only one original capacitor remaining - the output valve cathode bypass electrolytic - so I connected a replacement across it. This got rid of the distortion and increased the volume, so I fitted the replacement properly.
I noticed that the tone varied as the volume control was adjusted, which seemed a bit odd. With a meter across the cathode bypass capacitor I noticed that the voltage varied as the volume control was adjusted, which suggested that the volume control was somehow affecting the biasing of the valve. The pot is used as the grid bias resistor, so the bias resistance will vary from zero to 1M as the pot is adjusted, but this was the original design so should be OK. However the pot appeared to have been replaced previously so I checked the resistance. It was over 5M, which is far too high. I removed it and looked for markings - it was supposed to be 1M! I rummaged through my stock of used pots. I couldn't find any suitable 1M pots but had several good 500K pots. I selected one with the correct length shaft and fitted it. The tone now remained consistent with volume adjustment - as it should.
The sound seemed a bit thin - slightly lacking in bass. Since the volume control was a lower resistance than original, I tried increasing the audio coupling capacitor (C14) to compensate. It was originally 0.005uF. I tried 0.01uF (the correct value to compensate for the changed resistance of the volume control), which helped, but I decided that 0.022uF was better still, so I fitted that value.
As a test, I tried disconnecting the OA90 diode I had fitted across the Westector. Back to very weak reception again, so the Westector was clearly no good. I removed it and fitted the OA90 permanently.
Although the set basically worked, it still faded out as it warmed up, and the AGC didn't appear to be doing anything (weak stations were weak and strong stations caused distortion).
The detector and AGC arrangement in this set is unconventional, due to the need to design a set using valves that were available during the war. This is why the detector diode is a Westector rather than a valve. The most accurate and detailed description of the operation of this circuit is in Chas Miller's "Valve Radio and Audio Repair Handbook", so I referred to this for guidance.
It mentioned that the high value resistors in the AGC/detector circuit (R6, R7 and R8) going very high or open circuit might cause problems. Sure enough, all three were high, so I replaced them with modern types. I checked the rest of the resistors in the set while I was at it, and found R4 (6K8 HT decoupler to the screen grids of V1 and V2) was high at around 20K, so this was replaced too. The 47K resistor between the Aerial and Earth sockets had been replaced with a 4.7K component, so this was corrected.
On the next test the AGC appeared to be behaving much better, but there was now a significant buzz on the sound. Chas's book mentioned that the negative side of the main smoothing capacitor, C16, must be connected to the junction of R13 and T2, and not to chassis. I had connected it to the chassis - oops! When I replaced these capacitors I followed the original connections so repeated the mistake made by the previous repairer! With this corrected the buzz was gone.
However the set still only worked for a few minutes before fading away. With a meter connected to the AGC line it was apparent that the voltage was dropping. The AGC voltage from the detector was also dropping, and I was not sure whether this was the cause or the result. I was most confused by the fact that the voltage on the junction of R6 and R7 (suppressor grid of V2) remained constant at about 0.6V as the AGC varied. I connected a -3V supply (from two AA batteries) to the AGC line, to hold this at a fixed level. The fading problem was considerably reduced and the AGC voltage from the detector remained reasonably constant.
It was becoming apparent that either V1 or V2 was suffering from grid leakage as it warmed up. Conveniently the grid is the top cap so it was easy to disconnect each in turn while monitoring the AGC, which proved it was V1. Although I had tested the valves previously they had only been running on the tester for a couple of minutes - not long enough to show up the problem which occured after several minutes as the valve warmed up.
I was still confused about the fixed voltage on the suppressor grid of V2 - in fact I spent some time on this, before realising it was a red herring! Reading Chas's description carefully told me that this grid is pressed into service as an AGC clamp diode, so what I thought was a fault was actually the intended behaviour!
I asked in the Discussion Forum if anyone had a spare valve for V1 (ECH35, OM10 or X61M). A kind forum regular (Philip, aka "hotbulb") sent me a new Mullard ECH35 and also an EF39 (V2) free of charge! With V1 replaced, the set worked correctly. The original V1 was a BVA276, which is also a Mullard part.
I then tried the new EF39, comparing the AGC voltage with that obtained with the original. This showed that the new one was somewhat better so it remained fitted. However the original is still usable and was kept as a spare.
The IF transformer adjustments were still sealed from factory alignment, so I did not disturb them. C20 (aerial circuit trimmer) looked to have been adjusted, so I tuned the set to a weak station at the low wavelength end of the dial and carefully adjusted C20 for maximum reading on a meter connected to the AGC. I then tuned to a weak station at the other end of the dial and adjusted L2 for maximum. All other adjustments were still sealed so I left them alone.
The chassis was generally in good condition. I had already brushed the dust away, and felt it didn't need any further restoration. The valves were carefully cleaned.
The tuning scale is very basic, consisting of a printed metal disk rotating behind a fixed printed metal scale. Both parts had been removed before repairs started to prevent damage, but were rather dirty and needed some attention before refitting. I used foam cleanser to remove the surface dirt, followed by Brasso wadding which had a similar effect to using T-Cut on car paintwork. I took care with this since the paint and print are probably quite thin. Once the parts looked respectable, I finished them with Colron Finishing Wax.
The knobs were given the usual wash in warm soapy water then polished with Bakelite polish.
The plies of the top section were glued back together using Evo-stik woodworking adhesive. This was worked well into the gap with thin card before the job was clamped between two pieces of wood and left overnight to dry.
The surface of the cabinet was then carefully cleaned using Colron Wax Remover, and the paint spots etc were carefully scratched off with a fingernail. I did not want to sand the cabinet because the exposed bare wood was showing some "age" which I did not want to lose.
The cabinet clearly needed some sort of surface finish since the wood looked too light and the grain too pronounced. I was undecided whether to use varnish, wax or antique oil. I needed to add some colour but I did not want it to look too shiny. After some experiments on the inside base of the cabinet I decided on Antique Oil.
First I applied Colron Wood Reviver. This is probably best described as moisturiser for wood! It replaces the natural oils lost when strippers are used or just due to age and exposure. It is an oil-based product, which soaks into the wood and dries to give a good surface for oil finishes or waxes to be applied to. The Wood Reviver bought the original colour back to the wood - I was delighted with the results at this stage!
After 24 hours I applied Colron Antique Oil. Like the Wood Reviver, this soaks into the surface. It is left for an hour then buffed. Three applications were sufficient to give the surface a gentle sheen that seemed appropriate for the set. It is necessary to wait at least six hours between applications.
Fortunately, I found a piece of suitable fabric in my accumulation of useful bits and pieces. It had been removed from a scrap set - possibly a late 1940s Philips model but I'm not sure. It was the right colour and the right sort of age. It was reasonably clean but did not look too new.
I removed the remains of the old fabric from the speaker board, and then fixed the replacement fabric in place with UHU Spray Adhesive.
The set was carefully reassembled then left to play for a few hours to ensure there were no further problems. I am very impressed with the performance of the set - it is very sensitive (particularly for a short superhet) and the sound quality is very pleasing. It's better than some late 40s and early 50s sets I have restored!
Like many valve sets, it sounds better playing the right sort of music. I like listening to Saga 105.7FM (West Midlands) on it via an AM modulator. I don't think vintage sets should have to suffer the indignity of reproducing most of today's radio stations.
I am very satisfied with this restoration.
The overall appearance is pleasing and the sound quality is most pleasant.
Text and Photographs Copyright © 2004 Paul Stenning