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Old 21st Jun 2022, 12:55 pm   #1
jimscoper
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Default Vidor Lady Anne CT430

Rather foolishly I bought one of these at the boot fair. A couple of knobs broken otherwise cosmetically quite good.

However - dead. Reason is the output transformer primary is open circuit. Replaced with spare from junk box and radio works OK.

But why go oc? There was no circuit fault and even if the DL96 went short circuit I can't see enough current flow to burn out the winding. Maybe a short to ground.

The transformer is well coated in black bitumen stuff and I scraped the leadout wires to see if the problem was at the tagstrip end - no luck. Is oc transformer windings a common problem?

Put to one side, if I get very bored I might take it apart and rewind. Another one for the top shelf.
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Old 21st Jun 2022, 1:45 pm   #2
Heatercathodeshort
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Default Re: Vidor Lady Anne CT430

Age and chemical fumes from the dry batteries.
This is extremely common with B7G based valve portables. The valve holder pins can also fall apart once disturbed by general service cleaning.

The batteries give off very small quantities of corrosive fumes that rot the very fine wire that the primary is wound with. These radios are often discovered with an ancient set of batteries that almost guarantees that the OP transformer will be O/C. Note it is a very high impedance wound with hair gauge wire and the usual pentode type will give very low volume. Regards, John.
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Old 21st Jun 2022, 2:19 pm   #3
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Default Re: Vidor Lady Anne CT430

Open circuit output transformer primaries are extremely common in valve radios, it is the first thing I check when repairing one. At the 2021 Retrotech I bought three 1950s Bush mains 'woodies' , I was not at all surprised or even disappointed to find that all three had o/c output transformer primaries, Bush sets do seem to have a higher failure rate than some in this regard.
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Old 21st Jun 2022, 2:33 pm   #4
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Default Re: Vidor Lady Anne CT430

Yes you will find numerous threads about this if you do a search. That and valve holder pins are the bane of these old B7G valve portables. Even mains-battery types seem to suffer...my Bush BAC31 had a faulty output transformer (DL94 output valve).
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Old 21st Jun 2022, 3:39 pm   #5
jimscoper
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Default Re: Vidor Lady Anne CT430

Thanks everyone for the prompt replies. I am fairly old and learn something new every day. The replacement transformer is a RadioSpares type that claims it is for battery portables. Anyway it goes surprisingly well.

Waiting for some acrylic rod to drill and turn to size to re make the spigots and glue them on. May lash out of some fancy glue.

This model is built with a mains transformer to allow mains/battery working. I bought it not able to look inside and was hoping it had a battery eliminator to suit another radio - never mind.
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Old 21st Jun 2022, 7:38 pm   #6
Ed_Dinning
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Default Re: Vidor Lady Anne CT430

Hi Jim, yes I've rewound dozens of battery OPTs as well as a great number of DAC90/a types. Early battery set I?V transformers are the worst for failure, but often use 48SWG wire and hygroscopic paper insulation!
Ref the battery eliminators; if you search the forum you will find quite a few circuits for home brew types. The ones for 90V and 1.5 or 7.5 volts are simple to construct

Ed
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Old 23rd Jun 2022, 4:03 pm   #7
jimscoper
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Default Re: Vidor Lady Anne CT430

A bit more advice if possible.

The plastic knobs have broken spigots. I have turned down some acrylic (perspex) bar to suit the steel ring clamps and drilled for 1/4". Also used a Dremel to even up the remains of the spigot. I will add a sector of 6mm acrylic rod to accommodate the shaft flats.

The question is what glue to use. I have seen some methyl methacrylate glue but that is pricey and thin watery stuff. I think I need something a bit thicker but with the welding properties. Otherwise its going to be Wilko Hard Plastic glue backed up by Araldite.

Any ideas - preferably not too expensive?
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