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Old 9th Aug 2016, 11:51 pm   #1
Stuart R
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Default Vidor CN426 "Henley"

I was shown this set one night at Triumph car club, my friend found it whilst sorting through things at home and wondered if it would provide some entertainment on classic car outings.

It must have been stored in less than ideal conditions. The Cheney catches are rather pitted and rust is appearing where paint had been chipped. The base of the cabinet is rather warped and when sat on a flat surface, the set rolls around on the bulge in the case, rather than resting on its feet.

The rubber mains lead was taped-up in places, but there was a 3A fuse in the 13A plug. I dived in straight away and changed 'that' capacitor, C20 and put the electrolytics on my reformer before running the set up via lamp-limiter and then full mains. The set was silent, apart from a crackle when operating volume control, waveband switch or wiggling the valves.

The anode HT readings were all higher than expected, including V3's which just says 'Very Low Reading' on the Trader sheet. The output Voltage from the rectifier was around 15V low and I measured 2V across each of the 1.4V valve heaters.

Maybe in the past, someone has tried to give this radio a 'boost' by upping the heater voltages; I found that the heater ballast (R20) had a second resistor tagged across it, effectively halving its value. With the interloper snipped-out, the radio was still silent but heater readings returned to something more normal, between 0.9 and 1.2V.

For mains operation, the LT is derived from the HT. I'm not that experienced in the detail of HT and LT current flow, but imagine with these sets, any upset in the HT department will have a knock-on effect on LT and vice-versa. I decided to check out a few more resistor values. Most showed a 10% or less change, so were left in place, except for R14, (Output Valve Grid Bias) that was 65% adrift and, with a colour code I'm not familiar with, did not look very original. R1 (V1 Grid Coupling) does look original, but was the only other resistor with significant (20%) drift. I chose not to replace it as access around fragile coils looked tricky.

I've read a lot on these posts about the McMurdo valve bases failing so I went carefully around each base, prodding each half of the contact prong with a stout piece of wire connected to my meter to check the state of the valve bases. All pins, much to my relief, had solid continuity.

Also, (not recommended by all) I had carried out a blanket-change of all the TCC wax capacitors. I had done 'that' capacitor and the AGC decoupling as first choice, but they didn't help. I did check the set after each new capacitor was added, but still no change to the set's performance.

I was beginning to run out of ideas. I have an unidentified Ever Ready battery set on the shelf and although it felt a bit of a nasty move, I borrowed some of its valves for a short while. Swapping V1, V2 and V3 gave more signs of life and a reasonable hum was created when prodding the volume control contacts with a screwdriver. With the right combination of original and borrowed valves I could get the Anode Volts of V3 down to 30V, closer to the 'Very Low Value' than the 80V I had previously and very faint reception of Radio 5 Live.

At NVCF I had a good rummage around the valve stalls and got a complete set of NOS items for £8. Tried them when I got home and to my surprise, the set burst into life. Anode voltages are now very close to the Trader sheet, although screen voltages appear a little high still. I've now got 20V where 'Very Low Readings' are required on V3. I'm using my Maplin moving coil meter for this and it does load the set and make it quieter. Maybe the Trader's meter dragged it down further?

This is the first silent radio I've worked on where the only cure was a set of replacement valves. Frequently here, we advise newcomers that a family heirloom is unlikely to need valves to restore it to working order, but I understand that these battery valves are the exception, especially in this case when they have been over-run.

The tuning cord was looking rather frayed and slipped at times. Attempts to replace with NVCF-sourced tuning cord were not too good as it needed to be quite thin, to make multiple turns around the capacitor's drum. I managed to find a suitable thread in a local craft shop's bargain bin. Hopefully this will last as the tuning cursor was feeling rather too fragile on the last time I threaded the cord around its base.

The control knobs have also suffered, they appear to be moulded plastic. As they were removed, large cracks opened up on top of one of them. I repaired the cracks with a two-part epoxy resin, which made for a strong, clean repair. However, when re-fitting, another crack opened up further along! Maybe I should have carried out more thorough destructive testing to assess the damage before gluing? Each control knob is secured by a sprung, circular clip and I wonder if I should have removed these whilst the knobs have been removed from the set. I think the springs have 'relaxed' and tightened their grip on the collars, making the knobs extremely difficult to refit.

I removed the Cheney catches and gave them a clean with Brasso. A further problem with the damp storage meant that some of the fixing screws' threads were quite rusted. One snapped on removal and many didn't quite 'bite' when replaced.

The Rexine-type covering was covered with small paint spots which could be picked-off with a sharp-pointed tool. I tried a gentle going-over with warm, soapy water which removed some rust-staining under the catches, but it didn't really make a great difference to the overall appearance. I didn't want to try anything stronger for fear of removing the colour.

The mains lead and plug were replaced. The instruction sheet inside the cabinet shows that a two-pin mains plug can be stored within the cable tidy. Not so easy with a chunky three-pin plug, especially when the batteries are installed. For now, the mains plug is 'secured' by the loudspeaker cables. It's a bit close to the circuitry, so to prevent accidental contact, I need to find one of those plastic pin covers that get shipped on new appliance mains plugs. Hundreds of 13A-IEC leads that come through our office, yet I couldn't find any of these pin covers in the bin last week!

More on the batteries follows shortly....

SR

(Component references from “Trader” service sheet 1155 - pictures orientated OK on my PC!)
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Old 10th Aug 2016, 12:00 am   #2
Stuart R
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Default Re: Vidor CN426 "Henley"

The original idea was to use the set on classic car outings. There seemed no reason why it shouldn't work on batteries and I had a pile of Pound Shop PP3s from another Vidor project that hadn't got off the ground. Back to the Pound Shop for a set of C size batteries, I lashed them up on the kitchen table and the set worked well. Not sure how long they'll last as you can see the HT Volt meter 'counting down' as you listen. However, this seemed a good opportunity to attempt the manufacture of a reproduction set of batteries.

The set requires separate HT and LT batteries – Vidor obviously, for best results! Radiomuseum.org does have a few details of the dimensions for the L5536 (90V) and L5060 (7.5V) and Ever Ready equivalents. I found some useful scans of just the batteries required at www.royalsignals.org.uk/batteries and with a bit of trial and error with the printer scaling settings was able to print these on A3 at the required size.

The printouts were glued to cereal packet card then scored, folded and glued. The only trouble was that although the LT battery fitted within the radio case, the HT battery was just too long. I eventually had to abandon the full cereal packet HT solution due to time constraints.

In the meantime, I attempted to make some connectors to mate with the 2 and 3 pin battery plugs that were still inside the radio. I have since read about rolling tin around drill bits or recycling the material from coffee containers. My solution also used items from the kitchen as I used screw-on milk bottle tops as a mould for some old Milliput which needed using up. I opened up one half of a Lucar (automotive) female connector to accept the pins of varying sizes. I'd stabbed some holes in the bottle top and placed it between the battery plug and Lucar connector before filling the bottle top with Milliput. Before the putty set fully, I removed the battery plug.

The Result? Not brilliant. Because the contacts don't 'float' in the Milliput housing, it's impossible to insert the plug fully. However, the thickness of the completed cardboard battery case means that you don't need to push the connector fully home. In fact, with the cardboard and masking tape construction, the low insertion and extraction force help keep the Milliput housing in place.

I made up some corrugated cardboard inners to hold the modern batteries together and attempted to make some small notches and tabs to keep some small baffles in place to support the Milliput housings.

Unfortunately, the HT battery is the wrong shape to allow stacking the PP3s on their own studs, so had to solder small linking wires between each pair. I'm sure the 5 C cells would fit more easily in the LT case if my Milliput efforts hadn't turned out so thick. These had to be linked with small wires soldered to them, definitely no room for adding battery holders.

I was going to just leave the HT battery in the corrugated cardboard box, but I then found another of my mis-sized printing efforts, which although slightly too big, looks the part in the finished radio.

If I did this again, I'd have spent even longer perfecting the batteries. The cereal packet works well for the outer jacket, but I'd try and find some modelling card to make the inners and make a more accurate job of measuring and cutting. I wondered if laminating the A3 printout would make a glossy, longer-lasting jacket.

I would also consider adding a fuse as the metal mains cable tidy, bolted to the chassis does look worrying close to the HT battery's terminals.

That's all for now - hope it's of interest!

SR
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Old 10th Aug 2016, 7:22 pm   #3
TonyDuell
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Default Re: Vidor CN426 "Henley"

I think I have mentioned this in another thread, but 'my' solution (it is not orginal to me, but I use it) for the large size BS1363 plug not fitting into the mains cable storage compartment is to replace it with an IEC plug (is it a C14? The one you used to find on PC monitors). That will generally fit in the compartment, and all you need to connect it to the mains is a normal 'kettle lead' type of PC/instrument mains cable which seem to be everywhere.

When I needed the 'battery' sockets (actually to make batteries for an old valve hearing aid), I made them by turning, drilling and slitting brass rod for the contacts and drilling/milling a nylon block for the housing. It works well, but the result is bulky, and it took me a couple of afternoons to make them. Fun, but I would not go into production!
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Old 10th Aug 2016, 11:54 pm   #4
Phil G4SPZ
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Default Re: Vidor CN426 "Henley"

Nice write-up, Stuart, and it's good to read a success story that mentions the pitfalls encountered along the way, and the imperfections in the end result.

I also enjoy repairing battery valve sets and making replica batteries. For HT batteries, to make the sockets I use the inner conductors from female Belling Lee 'coax' in-line sockets, which are a perfect fit with the 3-pin plugs commonly used on battery sets. The coax socket inners are glued into holes drilled into a wooden block at the correct spacing, with a third blind hole drilled for location and polarity assurance. For larger (pre-war) style HT and GB batteries, 4mm I/D brass tubing is fairly cheap.
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Old 11th Aug 2016, 12:55 pm   #5
Stuart R
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Default Re: Vidor CN426 "Henley"

Thanks for your comments and tips. This was heavily edited - I had gone well into two sides of A4 originally!

The battery solution could have been a bit neater, but I really needed to get the set back to its owner in time for a car club day out. Final battery assembly was just the day before and It was just nice to return it in working order as a portable. As I handed the radio over, another friend pointed out that 'all he needs to find now is a 90V battery' and I was able to smugly reply that 'batteries are included'.

I've not really thought about keeping stocks of brass rods or tube as I don't have any precision tools for drilling or milling, so have to look at adaptations of what's around and easy to work with. I had thought about bootlace ferrules that are usually crimped on mains installation cables, but buying them in bags of 100, would have been costly to find the right size. If I can find the right size in a small 'selection pack', I think these would sit nicely in a drilled block of wood, nylon or cardboard sandwich.

As you say Tony, it's more of a labour of love to get these things looking nice. The experience gained here may encourage me to try some of yours and Phil's tips for the two 'My Lady Annes' on the shelf here. Phil's latest HT battery project looks very good.

I hadn't thought about the IEC power lead solution which would be quite neat, but would need to be sure the mating lead was suitably fused - rather than a 'hot' kettle lead at 13A. I had thought of a moulded 2-pin plug as I think they can be purchased with nice flex pre-attached and with the mains transformer inside, polarity shouldn't be an issue. In the end though, I opted to keep the set "as found" with regards to electrical wiring rather than "modified" since I am not the end user.

Best Regards,


SR
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Old 12th Aug 2016, 10:59 am   #6
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Default Re: Vidor CN426 "Henley"

For the mains lead - have you thought about using a lead with a 2-pin "europlug" on the end, and then using this in conjunction with a separate (suitably fused) 2-pin-to-13A-plug converter?

https://en.wikipedia.org/wiki/AC_pow...nversion_plugs

The "europlug" is conveniently small enough to be able to stash in the back of the radio without difficulty. Clip on the converter when you need it.
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Old 13th Aug 2016, 11:46 am   #7
Stuart R
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Default Re: Vidor CN426 "Henley"

Yes, 'Europlug' - that's what I meant. Those clip-together 13A plug adapters look ideal, but I'd have to supply a screwdriver for fitting, so a shaver plug adapter would probably have to be used.

But thanks for the link as I've never seen foldable plugs before and they look ideal. Can't see them available from the usual suppliers yet, but will keep looking.

Regards,

SR

Last edited by Stuart R; 13th Aug 2016 at 11:47 am. Reason: Punctuation.
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Old 13th Aug 2016, 12:57 pm   #8
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Default Re: Vidor CN426 "Henley"

Those adaptors are available from CPC. They do two versions I think, one for straight plugs and one that fits transformer units.
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