I've had a few of these radio's in the past, one when I had just left school some 50 odd years ago and classed it as 'just an old radio'.....I got rid of it when the drivecord snapped. The other one was more recent around 6 years ago which I restored and it worked very well especially as I only paid a tenner for it. A friend of a friend loved it so much when he saw it he paid me treble what it cost me....he still has it in pride of place in his living room. I then found another at a car boot but that turned out to be in rather a sad state, minus the UL41, various poor standard repairs, completely O/C smoothing caps, a shorted dropper section which had done nothing for the life of the valves and a missing back cover and base....I kept it for spares.
I have now just obtained another which I've decided will be a 'keeper'. It arrived today and I have to say that apart from needing a really good clean, it is in remarkable condition and only appears to have had a valve change (UL41). It looks as if it's been owned by a heavy smoker...or perhaps the whole family smoked. Typical brown stains over everything and a thick coating of dust inside. The best part about the set is that it is virtually cosmetically sound....by that I mean the the front illuminating escutcheon is complete with no cracks or bits missing, the knobs are not cracked around the shaft and it has a full complement of original screws. There is a slight stress crack in one corner of the Bakelite back but it is not right through and it should be possible to stabilise it. One slight cloud over everything was the fact that it was set to 200V. Always a bit suspicious since it came from a London area but if it's not been used for 40 odd years, there is just a possibility that it was used in a 200V area. There were still some around into the early 70's.
So firstly remove the back and base cover, remove knobs and intact felt washers, finally extract chassis from cabinet...anyone who has not worked on one of these before, removing the chassis also means removing the front illuminated escutcheon and make sure the tuning pointer as at one extreme end of the scale (it doesn't matter which end) so that when you extract the chassis, it doesn't foul the cabinet bottom front. If you don't do that, it's possible to bend the tuning pointer and/or pull the drivecord off the pulleys...and you know what Philips drivecords can be like......!!
So with the chassis on the bench (the speaker stays in the cabinet), next job is to give it a good vacuum. The chassis came up far better than I could have hoped. Very well preserved under all the dust. There are still some little nooks and crannies that need cleaning but overall it's come up very well.
While I was in the mood, I ran the valves through the Avo twin-panel tester. Rectifier and output valve near perfect, not so for the others. The UBC41 is very low and the UF41 is virtually dead. They may work well enough in the set of course but I have good replacements if necessary. I also tested the output transformer and got a healthy crackle from the speaker and the smoothing caps test very good so it all looks very encouraging at the moment.
That's about it for tonight. Next time I'll think about evicting the Philips 'tar bomb' capacitors. One has already started to erupt and they will all be as leaky as a sieve.
First shows the set as received, second the intact back cover, third the very dusty chassis, fourth with the front escutcheon and knobs removed prior to extracting the chassis, fifth, the extracted chassis with dust and sixth after an initial vacuum.
Update:
Managed to grab a couple of hours this evening and changed the critical caps.....audio coupling, tone corrector, common screen-grid decoupling, AGC decoupling and the 0.033 uF across the mains I replaced with a 0.047uF x cap rated at 300Vac. The tar bombs were all leaky and the one across the mains had started to erupt.
So now to first test....set mains to 160V, connect testmeter between HT reservoir cap and chassis and apply mains via a Safeblok.....easy to open if anything nasty starts to happen! I was reasonably confident that the smoothing caps would be OK but better to be safe than sorry....I have a healthy respect for them!
So with mains applied, the pilot lamp lit, dimly at first then got a little brighter as the heaters warmed up. Incidentally the wrong lamp had been fitted as I discovered on my initial inspection the other day. Someone had fitted a standard 6.3V 0.3 amp bulb. It would have been extremely dim or maybe not lit at all since it would have been in series with a 0.1A heater chain. I didn't bother to find out and just whipped the one out of the scrapper which was 20V at 0.1A.
So with a nicely glowing pilot lamp I watched the testmeter and it slowly started to climb towards 100V and beyond. At around 140V, a gentle hum came up and at 160V, some crackling. The smoothing can remained cold so I quickly checked tuning. Lots of noise here on MW and not surprisingly various buzzes and noises but no discernable stations. Wavechange and volume controls very noisy. Switched off and applied contact cleaner to wavechange switch and volume control. Second try was more productive and I was able to tune in R4 but it was just bordering on unstable with a slight tunable whistle. I increased the mains to 200V and the set went completely unstable with several stations tuning in with a whistle that would zero-beat when tuned spot-on but with audible distortion. Now several components could cause this problem and I had already replaced the IF decoupler which was the most likely component. As this is a 'bare bones' type radio with minimal decoupling it could also be caused by the HT smoothing cap being 'lossy'. Easy way to check is to temporarily bridge the HT rail with a 0.47uF capacitor (400V). This will filter out any RF getting onto the HT rail and causing the IF to become unstable. Well that didn't make the slightest bit of difference. So I bridged the new 0.1uF I.F decoupler and that didn't do anything either....What next? I remembered that the UF41 had tested very low on the Avo tester so on a whim, I tried a new valve...complete cure and lots more gain. I have no idea why the old valve caused instability but maybe there was some leakage as well. Whatever the cause the set was now working well so I went for broke and turned the mains up to 242v which is about the highest it gets here. The smoothing can remained cold so no problems there.
I left the set running for about 10 minutes, watching the HT voltage and making sure the smoothing can remained cold. An annoying intermittent crackle and rustling noise became apparent and I found by tapping the UBC41, the noise would come and go. Cleaning the pins of the valve made no difference so I tried another valve (from the scrapper). That cured the noises completely. The set is now working very well. It needs a good clean-up but I think the electrical side is done.
1st pic shows the new caps fitted, second shows side view after first switch-on, third, the power meter showing voltage and power in Watts, fourth, rear view during final test.
Major clean-up next....
The standard 4 valve plus rectifier superhet circuits used in the late 40’s and 50’s performed extremely well, nice repair.
A healthy respect for reservoir/smoothing cans is soon gained when you have seen the aftermath of one blowing its insides all over the inside of the radio/TV.
Frank
Good save.
These are simple "economy" sets without the crazy ideas that Philips loved so (too?) much. The black tar caps are something else, who made them I wonder, Philips?
Interesting to see another radio fixer on here, I thought I was the last one! The pictures on a radio are so much better and no eht.
Boater Sam
Glad that the output transformer proved to be good!- it looks of similar design to the type that we both found to be open-circuit primary in Philips 462As a while back. Apart from that, I thought that Philips tried quite hard, and often successfully, with their production engineering- those compact IFTs seemed to have been an early feature, it was only into the transistor era that some other manufacturers got them that compact, and that spring-clip fixing must have saved on time and parts-count. Fitting the main reservoir/smoothing can at the opposite end of the chassis to the dropper/rectifier/output hotspot smacks of knowing what they were at, too.
I always thought that the B8a/Rimlock gang were a pretty good bunch (the odd stumble such as the UL41 accepted), featuring very neat and short electrode-to-base connections and the signal valves often featuring lower heater current than their IO predecessors and B7g/B9a successors. They had a short reign in the UK, but that included being featured in some pretty grand multi-band AM sets before FM broadcasting took the market's attention. The European mainland manufacturers seemed to take them more to heart, even if the Americans spurned them.
The 4 + R format served well for a long time indeed- I suppose that once the signal pentode had displaced the signal tetrode, followed by the triode-hexode/heptode and double-diode-triode becoming more-or-less standard in the mid-thirties, then the format had a nigh-on thirty year reign. The valves got smaller and more highly refined, but the basic circuit hung on well.
The 4 + R format served well for a long time indeed- I suppose that once the signal pentode had displaced the signal tetrode, followed by the triode-hexode/heptode and double-diode-triode becoming more-or-less standard in the mid-thirties, then the format had a nigh-on thirty year reign. The valves got smaller and more highly refined, but the basic circuit hung on well.
That's what I like about valve radio's. You can pick up virtually anything from the late 30's through to the 60's and even without a circuit it's not too difficult to work out what does what. You might need the valve data if it uses unfamiliar valves and it helps if you 'grew up' with valve sets but the basic 4 + 1 circuit stood the test of time.
Well done with the restoration. That's a good looking radio!
Interesting that the power handling valves were good while the small signal valves were iffy. Perhaps the former were replacements?
Agree with the 4+R format, it was a sweet-spot of cost / performance.
In the early 60s I would work out valve pinout by peering into the envelope. Of course this worked best with Noval valves. At that time I had no data books and only the occasional schematic as examples.
I was never keen on Rimlock, the connectivity was never as good as Octal or B7G / B9A.
I was never keen on Rimlock, the connectivity was never as good as Octal or B7G / B9A.
It was the glass pip that I hated. Until I became enlightened to the 'spring clip' on certain B8A valveholders, I killed a few B8A's simply by pulling them out of the socket. Now if I have the 'spring clip' type, I take the spring off
Well done with the restoration. That's a good looking radio!
Interesting that the power handling valves were good while the small signal valves were iffy. Perhaps the former were replacements?
Thank you.
I'm surprised about the rectifier...it's an original Philips Miniwatt type, almost certainly the original and emission-wise it's right up there. The UL41 was a replacement at some time. No manufacture mark on that but I suspect it's a Pinnacle since I have a new replacement that looks identical. The small signal valves are all originals. Strangely enough I've had a couple of UF41's with very low emission.
I always thought that the B8a/Rimlock gang were a pretty good bunch..... the signal valves often featuring lower heater current than their IO predecessors and B7g/B9a successors.
That was a poor choice of wording, really- especially as a series heater string radio is the subject of the thread, "lower heater power" would have been better.
Spot of straw-clutching- I wonder if the radio had spent much of its existence tuned to one (or a handful) of strong local station(s), with FC and IF biased right back by AGC, and the cathodes had got a bit lazy? I've been surprised at just how high (negative) the AGC volts can go with a really strong signal.
Update:
Finally got round to finishing this radio. I did the electrical side some weeks back and that was all working well. The cabinet was dirty and the front grille that illuminates was covered in nicotine stains. Warm soapy water worked wonders for the cabinet.....you should have seen the colour of the water! I don't generally like getting bakelite too wet but this cabinet came up really well. The front grille responded to foam spray and I was very pleased with the result. The decorative screws came up almost like new after treatment in the ultrasonic bath. I left the grille to dry and a final rub over with a dry cloth was all that was needed to bring it up almost like new. Same with the decorative screws. Once the cabinet was dry, I gave it a good rub over with Polishing Paste No. 5 also known as Bakobrite. Very little effort was needed to bring up a good shine. The knobs were in very good condition and the centre brights came up very well.
Reassembly was straightforward and the end result was very satisfying. It's the best example I've seen of one of these sets.
First shows the cleaned grille, second the decorative screws refitted after an ultrasonic bath, third, the cabinet before the grille was refitted, fourth, the assembled radio, fifth the grille illuminated.
The radio works really well for what is essentially a 'bare-bones' circuit. I can receive Capital Gold almost interference free by rotating the set, far better than radio's with an external aerial and this set just has an internal loop. There is so much local interference it shows that a lot is airborne.
Wow! Rich, that looks stunning now 👍
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