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Success Stories If you have successfully repaired or restored a piece of equipment, why not write up what you did and post details here. Particularly if it was interesting, unusual or challenging. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

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Old 28th Feb 2021, 5:41 pm   #1
Beardyman
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Default Tesla 308U

This one has been loafing around for a while & when it was purchased it was a bit of a bargain. Nothing wrong in that but I had my doubts. The cynic in me asks, "Why so cheap, whats wrong with it?", we've all been there.
At the beginning of February I decided to take a look, just a general survey as it were. Definite signs the Phantom Twiddler had been abroad, wax seals of IF can cores disturned, several other adjustable cores the same. Ah well, here goes then. I was pleasantly surprised to find all the resistors were OK! Admittedly some were on the edge of things but still useable. The black capacitors were another story, all way over and/or leaking. I decided to re-stuff them to keep the general look as it were, that black tarry stuff is truly awful. The double reservoir capacitor re-formed well, less than 1mA leakage current at 250VDC. All the silver mica & ceramic capacitors were spot on. There was a couple of moulded caps that had cracked & unfortunately I was unable to preserve them, they were replaced by modern parts. All the filaments were intact, phew! Mains switch was good, band switch contacts were very blackend but a few hours with a cotton bud & some Servisol brought them back. The speaker in these sets is tiny, about 3"-4" across, the result is quite a tinny sound when compared with the bench speaker. Although, generally, well constructed there are a few obvious places were corners have been cut, one of which is the lead outs from the speaker go directly to the output transformer, these are Litz wire, horrible stuff. Only a few strands were making contact on one lead, the consequence was that the output was very quiet, took a while to track that down!
As these sets are AC/DC all the relevant pre-cautions were taken. New scale bulbs fitted (these are in the neutral return), voltage selector checked for 220V, powered up via an isolating transformer & variac. At around the 200V AC mark the scale bulbs were just glowing, no smoke, all good, cranked up to 220V AC & there were signs of life. All three wavebands got something but very difficult to tune. After a look at the alignment instructions I felt a little crest fallen, I don't (as yet) possess an RF signal generator. I decided to go for the "tune for maximum volume" technique just for MW for the time being. After about a half hour or so things were improving nicely, good volume, clear & undistorted. Tuning was far less knife edge too, bonus. At this stage I tackled the case. I have no idea what the black stuff was in the grill of this radio but it took forever to polish off. I tried everything I have & plain old Autosol worked the best but still not a quick job, in total I think I spent the afternoons of three days just cleaning the case. Was it worth it? Yes, yes it was. These sets do look very pleasing & hark back to a long gone era, to me they look 40's but this set was manufactured on 7th July 1956. The date is stamped on the back of the tuning gang!
The rear card was intact but heat damaged in one corner, nearest the dropper oddly enough! This set does run hot but no hotter than say, a Bush VHF90a.
All the valve bases & valve pins needed to be throughly cleaned as well. All in all a not unpleasant set to work on.
The knobs are not original, I did look into trying to get hold of some but after seeing the prices I decided to give it a miss, the one's it has will work perfectly well.
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Old 1st Mar 2021, 8:39 am   #2
cathoderay57
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Default Re: Tesla 308U

Nice work. I've attached a couple of photos of mine. I bought it in a second-hand shop in Prague quite a few years ago. You're right that it does run hot - mine so much so that I rarely use it. I did try it on the 115v setting via an autotransformer but it still got pretty hot on top. I think it would be a good candidate for a capacitive dropper and I might get around to that one day. Nice display piece though so meantime it sits happily on the shelf collecting dust! Cheers, Jerry
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Old 1st Mar 2021, 9:40 am   #3
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Default Re: Tesla 308U

I have just read your write up whilst enjoying my first cup of coffee the maroon one is less common than the brown one there is also a black one made I have all three in my collection like Jerry I purchased the maroon one in the Czech republic ,I like a radio that's been loafing around , you keep looking at in passing, then one day its on the bench, well done with the restoration, you do need to arm yourself with a signal gen , something you could ask for on the wanted section you never know . Mick.

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Old 1st Mar 2021, 2:17 pm   #4
newlite4
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Default Re: Tesla 308U

These sets although fairly standard in their design tend to be challenging due to their rather flimsy construction. I did a 307U and a 308U in the autumn and found that the oscillator coils on the above chassis right were very exposed and needed some repair due to the ham fisted attention of the phantom bodger. I think that the design is essentially Philips based which adds to the difficulties encountered along with the twitchy U21 series valves. Just like the original poster has mentioned, the sound from the small speaker is lacking. Well done for breathing life into this one, they are good lookers.
Neil
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Old 3rd Mar 2021, 8:05 am   #5
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Default Re: Tesla 308U

I have found there are several variants in regards to diagrams & component values. Took a while to get my head round the fact that all capacitor values are in pF. Yes, the coils do seem rather exposed & prone to damage. That being said it's testament to the design that they survive this long. The thing that intrigues me is how did it get to this country? If only they could talk!
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Old 6th Mar 2021, 3:23 pm   #6
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Default Re: Tesla 308U

Some pictures.
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Old 6th Mar 2021, 6:16 pm   #7
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Default Re: Tesla 308U

Hi you got me thinking about a capacitance dropper ,doing a bit of checking with one of mine ,yours is looking good ,nice to see the dial has survived , what would finish it off is a set of knobs more in keeping , Mick.
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Old 9th Mar 2021, 7:54 am   #8
Beardyman
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Default Re: Tesla 308U

I did have a look around for the correct knobs but was put off by the prices! Some may well turn up in the future so for now these ones will do. I did have a look at the capacitive dropper myself as there are a couple of other sets I have that could benefit from a little less heat. Either that or a fan of some kind, when under run they can be near silent. There's plenty of space for a compact type in there & I do have a couple of small transformers that would drive it. We shall see, probably later rather than sooner!
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