Vidor My Lady Catherine CN435Z: Questions before attempt to revive

[granazis]

Originally Posted by Cobaltblue

Nice one I have a bit of a thing for these little portables so it's always good to hear of someone going the extra mile to get a result.

Cheers

Mike T

Thank you for the help and direction.

[granazis]

Originally Posted by Station X

Well done. We like happy endings here. Your methodical approach has paid dividends.

Thank you

[Cobaltblue]

Originally Posted by granazis

I have looked for it but could not identify it on the PCB, It's not where the photos of the non-PCB models show.
On the PCB many capacitors are labeled: C16, C17, C18, C19... but no C20 or 21 I could see.

Apart from the black "orrible hunts" all the other capacitors I could see around the audio stage are Eire disc disc ceramics and these are normally fine,

I suspect the numbering on the pcb is different from the circuit diagram. It's a bit tricky and partially guesswork but attached is where I "think" C21 from the circuit diagram is.

Cheers

Mike T

[Sideband]

Yes it shouldn't be too difficult to 'reverse engineer' the circuit around the output stage. You have a circuit so you know what components to look for. Find the anode of the DAF audio valve and the grid of the DL output valve (the corresponding pin numbers of the valves should be shown on the circuit diagram or perhaps a separate diagram and the capacitor coupling between the two has to be the audio coupling capacitor. If it's a ceramic type, it's probably ok. If it's a waxy...well you know the answer!

[granazis]

Originally Posted by Sideband

Yes it shouldn't be too difficult to 'reverse engineer' the circuit around the output stage. You have a circuit so you know what components to look for. Find the anode of the DAF audio valve and the grid of the DL output valve (the corresponding pin numbers of the valves should be shown on the circuit diagram or perhaps a separate diagram and the capacitor coupling between the two has to be the audio coupling capacitor. If it's a ceramic type, it's probably ok. If it's a waxy...well you know the answer!

Yes, that's what I plan to do, but visual inspection showed no capacitors other that C16-C19. There is an electrolytic one too, in the middle of the PCB. On the schematic I use (for CN343) any electrolytic capacitor.
Meanwhile, the radio played for nearly 3 hours now, 1 non stop.
There are a few issues with the reception.
Nothing on LW.
Some weaker stations seem to fade after a while or as I move the cover (that houses the antenna.) I attached to it an active antenna and there was improvement but the only station that is always getting through it Talksport on 1053 & 1089 (on the dial are between 300m - 250m - near 250)
It receives on MW stations between 558 (Punjab Radio) to 1305 (Premier) - including BBC4 on MW, and Radio Caroline (in the evening too).
I opened it and I found that from the antenna (there are apparently 2 loop antennas on the cover - no ferrite rod) 3 cables are coming out: yellow, red, black (see photo). The black one was not connected anywhere. I soldered it to the most likely point - to the chassis at another yellow cable at the lower part of the photo. But the improvement is marginal.
I am planing to remove the cover of the antennas (L1 & L2 on the schematic) to see what's going on there.

[granazis]

Originally Posted by Sideband

Yes it shouldn't be too difficult to 'reverse engineer' the circuit around the output stage. You have a circuit so you know what components to look for. Find the anode of the DAF audio valve and the grid of the DL output valve (the corresponding pin numbers of the valves should be shown on the circuit diagram or perhaps a separate diagram and the capacitor coupling between the two has to be the audio coupling capacitor. If it's a ceramic type, it's probably ok. If it's a waxy...well you know the answer!

Sorry it wasn't uploaded

[Station X]

Personally I'd just check the frame aerials for continuity, bearing in mind that they may effectively be short-circuited depending on the position of the wave change switch. Also check that the wires go to the correct place.

[granazis]

Originally Posted by Station X

Personally I'd just check the frame aerials for continuity, bearing in mind that they may effectively be short-circuited depending on the position of the wave change switch. Also check that the wires go to the correct place.

Thank you. Will do so.
Do you agree that the black wire is grounded to chassis?

[Station X]

If you're asking whether the black wire should be connected to chassis, the answer is I cannot say, but it seems likely. It seems the logical point for it to go to assuming neither of the other two wires are grounded.

If the coils have appreciable resistance it should be possible to identify the common point by taking resistance readings.

[granazis]

At this point the radio is working well - I use an active antenna (Degen DE31MS) for reception. Now the reception is stable, it's been playing next to me for half an hour now and continues without the signal fading.
With the 9v power consumption of a few mA the 10X9v "pack" I have made (@ 86v) is going to last for a while. The 1.5v (1.38-1.42) will probably need replacement sooner.
The audio quality is not better than that of the transistor radios of the late 1950s. I expected better from a valve radio of the time. I have an EKCO U355 (1959) and has better audio quality than many modern "DAB Radios!"
I have a number of vintage radios that either I haven't seen working or have recently stopped working, so I am looking forward to begin the next restoration project in the upcoming weeks. I'm between two transistor radios: a BUSH TR90D (1964/65) that I have never seen working and a Swiss made GAUERS VHF (1961, has LW/MW & VHF 110-135 MHz) that worked on my hands a couple of times and I suspect it's problem in the rather complicated side-switches.

[granazis]

Originally Posted by Station X

Personally I'd just check the frame aerials for continuity, bearing in mind that they may effectively be short-circuited depending on the position of the wave change switch. Also check that the wires go to the correct place.

Now LW works too. Only BBC 4 there now not for long.

[Station X]

Four posts moved to a new thread here:-

https://www.vintage-radio.net/forum/...d.php?t=209547

[Techman]

Originally Posted by granazis

I fed 1.38v to the LT connection and 86.4v to the HT (used a mix of new and used 9v batteries to get under 90v as the brand new were giving me 98v. I don't know if the valves can stand that.

You won't hurt the valves with 98 volts HT, it's the LT side you have to be more careful with regarding overvolting. The original 90 volt radio batteries were always over their stated voltage when brand new anyway. Always try to use zinc carbon batteries for the HT, rather than the alkaline type. I've found that my local Poundland seems to have stopped selling my favourite zinc carbon PP3 batteries and now only seems to stock the alkaline types, so it's a case of buying on-line now.

[kalee20]

Why do you say that, Techman?

I tend to use alkalines as a matter of course - voltage is more steady with discharge.

(They do pack a much higher punch of course, if you happen to short-circuit them - 90V of alkaline battery is not to be trifled with!)

[granazis]

Originally Posted by Techman

You won't hurt the valves with 98 volts HT, it's the LT side you have to be more careful with regarding overvolting. The original 90 volt radio batteries were always over their stated voltage when brand new anyway. Always try to use zinc carbon batteries for the HT, rather than the alkaline type. I've found that my local Poundland seems to have stopped selling my favourite zinc carbon PP3 batteries and now only seems to stock the alkaline types, so it's a case of buying on-line now.

At the moment I use zinc-carbon as advised for the 90V, two slightly used from Poundland, and 8 I got online, and alkaline - slightly used to so it gives 1.38 - for LT.
It works great for hours and hours so far. I really like that I can have a valve radio that I can move around the house or have at the bedside.
Now getting another LW station too. In french on 1200m so it must be Algiers on 252KHz. Without any external / active antenna.
Also stations now on MW without an active antenna, although for listening I do use the active antenna for louder audio. The MW freq range seems 522-1350 KHz. I would like it to go a little higher...

[kalee20]

Yes, self-contained valve portables are really useful and this typical 4-valve superhet is hard to beat, especially considering its simplicity!

I regularly use a Vidor CN420a and an Ever Ready Model K - the Vidor has clocked up well over a thousand hours since 2009, all on the same set of valves (but the LT supply is precision regulated at 1.38V).

Happy listening!

[Techman]

Originally Posted by kalee20

Why do you say that, Techman?

I tend to use alkalines as a matter of course - voltage is more steady with discharge.

(They do pack a much higher punch of course, if you happen to short-circuit them - 90V of alkaline battery is not to be trifled with!)

That's the exact reason. I've got at least a couple of true stories of near accidents when using this type of battery.

There's probably amps rather than milliamps available from a 9 volt alkaline battery if it's shorted out, so 90 volts worth is a seriously dangerous power supply if something should go wrong in the middle of the night. There's so little current needed for the HT supply in these radios that ordinary zinc carbon types are easily sufficient, and if anything should go wrong while your back is turned, then the source is likely to be killed before any fire is started. You could argue that an in-line fuse would be a good addition with an alkaline battery source, and it would be, but what if something should go wrong with your wiring inside the battery pack itself? There's always a risk, but minimising it if you can is always best.

[G6Tanuki]

If you want to hear some DX stations on MW, try listening at the low end of the band at night. There's a station down that area that is in North Africa and runs near on a Megawatt, relaying 'jil FM' with a good range of Arabic rap tunes, and what we used to call ~rai~ music.

It would be a good catch , to be able to say that your radio had received a station on another continent!

Tune around 500-600 Metres on the dial and see what shows up

[Graham G3ZVT]

Originally Posted by G6Tanuki

Tune around 500-600 Metres on the dial and see what shows up

531kHz in new money

[kalee20]

Originally Posted by Techman

That's the exact reason. I've got at least a couple of true stories of near accidents when using this type of battery.
...
You could argue that an in-line fuse would be a good addition with an alkaline battery source,

OK. Makes sense.

Actually, a fuse (or the choice of) might be tricky - if I used one it would definitely be a 1.25" fuse - a 20mm fuse might not break the circuit once an arc has formed with 90V DC behind it!

I do have an overload trip circuit using a MOSFET, developed with a friend - though as a fail-safe device it leaves a bit to be desired as MOSFETs fail short-circuit.

I've not lost any sleep with alkaline batteries at 90V but I do make sure the wiring is beyond suspicion!