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Old 10th Apr 2021, 8:59 pm   #1
Gabe001
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Default The taming of the shrew - the defiant "Defiant"!

This is an account of the restoration of a Defiant M234, a relatively uncommon set which I acquired from an auction recently. There is very little literature regarding this set and no circuit diagram, so I do hope that this account helps someone in future.

The "Defiant" was the Co-op's own radio brand. They wanted to sell radios, but the major brands wouldn't work with them as they considered the Co-op a discount store. So they developed their own. It is possible that the sets were actually manufactured by Plessey. The speaker and all capacitors are Plessey products from what I could tell.

First impressions of the radio were good. The case was well made, except for some cracking and loss of varnish on the sides. The veneer was thick and intact. The dial which I believe is a simple celluloid strip was badly warped, and there were a few light scuffs to the wood. All the valves were present and the chassis was clean. The dial pointer moved freely and all knobs were present. The wires to the speaker were disconnected, and an HT choke had been fitted on the output transformer The speaker was the original Jensen electrodynamic. I was looking forward to restoring my first TRF pre war set.

Cosmetic restoration was straightforward. All knobs came off without issue (grub screws). The lightly cracked veneer responded to some burnishing cream and a light coat of shellac. I'm not the best at applying french polish, but it turned out well. The warped celluloid dial responded to gentle warming in the oven for 20 mins at 60 degrees. I flattened it using heavy books but I had to do this process twice.

Electrically however it was a disaster. The phantom twiddler had been hard at work....
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Old 10th Apr 2021, 9:38 pm   #2
Gabe001
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Default Re: The taming of the shrew - the defiant "Defiant"!

For the electrical bits, I have to thank Jerry (cathoderay57) for his help and advice and encouragement; I did have quite a few questions. I was also luckier than most in that this set came with a photocopy of the circuit diagram, which will now be part of the next BVWS schematics CD.

Where to start..

The phantom twiddler had:
Switched the uu3 for a uu5 valve
Fitted an HT choke with a DC resistance of 450ohms on the output transformer
Disconnected the connections to the speaker
Fitted a dual 32uf can as reservoir and smoothing caps (excessive for a uu5). This can was attached with a mounting clip and double sided tape.

The first step was to trace out the leads to the speaker, label and attach them. I knew that the speaker field coil should have had a DC resistance of 2500ohms. This actually measured 2200 in my set - close enough. The primary of the output transformer measured 390 ohms which is what I expected. So far so good. It was easy to work out what was connected to what.

The dial 32uf can was removed and the reservoir cap was replaced with a 500v 4uf and the smoothing with a 450v 10uf. The set was originally fitted with a 4/6uf combination. I also permanently removed the connection from mains to the aerial, for safety

The grid coupling capacitor was replaced, as usual, and after checking the one-off switch and the transformer primary I prepared for first switch on via the lamp limiter.

Unfortunately the lamp limiter remained bright, indicating a short. I spent the good part of a day trying to find out where this was. Despite removing the rectifier valve, then all the valves, then the various transformer connections got HT,LT etc, the bulb remained bright. The transformer was getting hot. I got some advice from here and everyone suggested a transformer with shorted coils. Ed Dinning came to the rescue with a ne transformer which arrived in the post a few days later.

This new transformer however required new mounting holes in the chassis, something I had never done before. With some advice, and some luck, and paranoid use of masking tape, the drilling was completed and turned out to be easier than I expected. Still a relative novice, it took me a day to transplant the transformer and a few more hours to reconnect the new one. Luckily Ed labelled the transformer wires for me, which made things easier.

Time for first proper switch on....
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Old 10th Apr 2021, 10:01 pm   #3
Gabe001
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Default Re: The taming of the shrew - the defiant "Defiant"!

.... And this was very underwhelming. The good news was that the lamp limiter was behaving as it should. I also had very faint reception on both bands (mw and LW).

At this point however, I had 3 problems

Volume was very low, even on gram
Sound was distorted
HT about 40v too high

In a nutshell, the ac2/Pen was low emission, and all the resistors were very much out of tolerance, so they all needed replacing. The paper caps would have to be changed too. The collectable Plessey 1uf metal cap measured 4uf with my meter so that had to be replaced too. In essence, I spent a day replacing all passive electrical components, put a new mains lead, earthed the chassis and cleaned the waveband switch. The volume control was very crackly at first but seems to have sorted itself out after some use.

Meanwhile, Jerry sent me a good ac2/pen. Things improved a lot. Volume came up and a lot of the distortion was corrected. HT was still high but closer to what it should be. This was unsurprising as the uu5 is more efficient than the original uu3. I was tempted to try and look for a UU3 but I'm not sure it would have been happy with 350v on the plates. In the end I used 2 470ohm 5w resistors to get the voltage down to where it should be. They don't get particularly hot.

I was almost there, but not quite. I was still unhappy with the sound quality.

The speaker voice coil was rubbing and I needed to recenter it. Never having done it before it took me a few hours. Things aren't perfect but the set sounds better now.
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Old 10th Apr 2021, 10:20 pm   #4
Gabe001
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Default Re: The taming of the shrew - the defiant "Defiant"!

Final verdict

The set looks stunning and the pictures don't do it justice

From an electrical and technical perspective I own another pre war set, a pilot u650, and there is simply no comparison. The components in the defiant don't seem to age well. I suppose you get what you pay for.

In its defence, despite being a TRF set it performs reasonably well. BBC radio 4 on LW came in loud and clear and mw reception was acceptable. The sound through the pickup is a bit "muffled" compared to a radio station, I'm not sure why, but playing the same tunes with a pantry transmitter makes them sound much better compared to playing them directly.

Video below of the defiant playing some 50s tunes using my cheap chinese pantry transmitter (the minimod is in the post).

https://youtu.be/Nkiz7jMl9sc

Hope you enjoyed the write-up

Gabriel

Ps: I typed all this on a mobile phone and noticed some predictive text errors which I apologise for

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Old 11th Apr 2021, 12:10 am   #5
Skywave
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Arrow Re: The taming of the shrew - the defiant "Defiant"!

When I was in my early teenage years, my parents bought me a Defiant transistor radio for one Christmas. At that time I had an uncle who worked for Plessey and he told me that, yes, Plessey produced the defiant line of radios for the Co-Op.

Al. / Apr. 11
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Old 11th Apr 2021, 10:28 am   #6
cathoderay57
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Default Re: The taming of the shrew - the defiant "Defiant"!

Nice work and worth all the effort. Jerry
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Old 11th Apr 2021, 12:28 pm   #7
Lloyd 1985
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Default Re: The taming of the shrew - the defiant "Defiant"!

Very nice radio, we don’t see many Defiant’s on here, or at least, I’ve not noticed them! Looks a nice clean layout under the chassis too.

Regards
Lloyd
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