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Old 10th Feb 2016, 10:29 am   #21
gary_crutchley
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Default Re: Vidor CN430 My Lady Anne

Thanks David,

So what are the likely causes of a fault like the OPT primary failing please? It looks as though the DL96 has also failed.

I guess I'm thinking ahead, I don't want to replace components to have the fault occur again.

Once again, I really appreciate the help.

Regards,

Gary
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Old 10th Feb 2016, 10:34 am   #22
Phil G4SPZ
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Default Re: Vidor CN430 My Lady Anne

Quote:
Originally Posted by paulsherwin View Post
...an open circuit output transformer primary. This is quite a common fault...
It sure is. My understanding is that in this type of transformer the primary winding was wound with extremely fine wire which gave it a relatively low DC current-carrying capability. Any DC leakage across the output valve's grid coupling capacitor ("that capacitor") causes the valve to pass more current. The first the user would know about this was reduced HT battery life, and given the high price of HT batteries, many of these sets were pensioned-off before the output transformer could be damaged, but the mains/battery models could continue to be used on mains until either the distortion became unbearable or the transformer failed.

At one time you could find RS Components miniature output transformers which made ideal replacements. Sorry but I've used all the ones I had!
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Old 10th Feb 2016, 11:09 am   #23
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Default Re: Vidor CN430 My Lady Anne

Hi Phil,

That's very interesting. I was advised earlier that the output valve's grid coupling capacitor was silver mica in this set and did not need changing. It certainly isn't a 'waxy', I've checked. If it helps I can get a picture of it.

Do I need to consider changing 'that' cap in any case?

It looks like I have someone who has both an output valve and a transformer, my lucky day!

Regards,

Gary
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Old 10th Feb 2016, 12:30 pm   #24
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Default Re: Vidor CN430 My Lady Anne

Quote:
Originally Posted by gary_crutchley View Post
...I was advised earlier that the output valve's grid coupling capacitor was silver mica in this set and did not need changing. It certainly isn't a 'waxy', I've checked. If it helps I can get a picture of it. Do I need to consider changing 'that' cap in any case?
Not necessarily, Gary, as some later models used a disc ceramic or other types of capacitor in this position, and they are generally OK. It would be worth applying power to the set and checking for positive volts on the control grid of the output valve, with a DMM (not your Avo 7!) but you may just have been unlucky and the output transformer failed for other reasons. Anyway, good to know you've located a transformer and valve.
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Old 10th Feb 2016, 12:40 pm   #25
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Default Re: Vidor CN430 My Lady Anne

With power applied measure the voltage on G1 of the DL96 (pin6). If it's positive then "that" cap will need replacing. As it's a ceramic type I'm 99.9% certain it won't need replacing. There's no harm in getting a spare DL96 although it may be worth getting a DK96 but wait until the transformer has been replaced before doing so.

Keith
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Old 10th Feb 2016, 1:10 pm   #26
gary_crutchley
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Default Re: Vidor CN430 My Lady Anne

Thanks both. It looks like I've been lucky with the transformer. I will check the voltage on the control grid. Now that I found a valve fault I will give each of the valves from the Vidor a quick test in the Ultra that I have. That should tell me if the others are okay.

Regards,

Gary
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Old 13th Feb 2016, 6:00 pm   #27
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Default Re: Vidor CN430 My Lady Anne

Hi all,

I have an update on this set.

I obtained an output transformer and DL96 from Vinrads so today we were ready to do some more work on the Vidor CN430.

If you recall my previous posts I said that I had tried the valves from my Ultra R825 in the Vidor, but it didn't work. What I hadn't done was try the ones from the Vidor in the Ultra one by one to prove they were working. I did that and found that the DAF96 isn't working, so now I need one of those. For the purposes of the work planned I borrowed the one from my Ultra.

We installed the replacement output transformer, which took a while. The replacement was a suitable size but didn't have any fixing brackets to allow us to fix it to the chassis. So we had to remove the frame from the old transformer which fitted reasonably neatly around the replacement.

We installed all of the valves and powered it up on the lamp limiter, the Vidor immediately burst into life. We were able to tune stations on both bands. The volume wasn't as high as I anticipated, but at this stage we haven't changed any capacitors.

As the radio worked we decided to quit whilst we were ahead and attempt to obtain a replacement DAF96. The valve holder for that valve in my Ultra R825 isn't perfect, so I didn't want to risk damage by repeatedly inserting and removing the valve.

Once I have a replacement valve I will recheck the voltages and the grid coupling capacitor. Then we will change the wax capacitors one by one.

At least we know the radio is working, I very pleased with that outcome.
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Old 13th Feb 2016, 6:54 pm   #28
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Default Re: Vidor CN430 My Lady Anne

Hi Gary, I would say do the caps now and do not risk new valves with possibly bad caps,

Ed
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Old 13th Feb 2016, 7:39 pm   #29
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Default Re: Vidor CN430 My Lady Anne

Agreed. The wax caps are decoupling the screen grids and the AGC line. Any leakage in these can affect the performance of the set.

Keith
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Old 13th Feb 2016, 11:18 pm   #30
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Default Re: Vidor CN430 My Lady Anne

Thanks Ed and Keith,

Thanks for the advice I appreciate it. I do intend to change all of the wax caps, one at a time testing as we go.

Interestingly I noticed something when we removed the output transformer. As I said above we reused the frame, so I had to remove the paxolin tag strip from the top. When it parted company with the transformer the leads to the secondary remained attached, however, those for the primary just lifted straight out of the transformer body.

I suspect that connections may have failed rather than the windings having gone open circuit.

Regards,

Gary

Last edited by gary_crutchley; 13th Feb 2016 at 11:19 pm. Reason: Typo
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Old 14th Feb 2016, 2:37 pm   #31
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Default Re: Vidor CN430 My Lady Anne

Gary, I have several DAF96 valves, and you are welcome to have one on the same basis as last time. I'm not going to be at the museum for a few weeks, so if you'd like it sooner please PM and I'll post it to you.
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Last edited by Phil G4SPZ; 14th Feb 2016 at 2:40 pm. Reason: Punctuation
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Old 14th Feb 2016, 9:21 pm   #32
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Default Re: Vidor CN430 My Lady Anne

Thanks Phil,

I sent you a message.

Regards,

Gary
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Old 21st Feb 2016, 1:17 pm   #33
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Default Re: Vidor CN430 My Lady Anne

When I restored my Vidor CN381B I found the transformer open circuit (caused by faulty C18 .01uF to the final valve grid).
I found a replacement from RS P/N 210-6475.
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Old 21st Feb 2016, 8:35 pm   #34
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Default Re: Vidor CN430 My Lady Anne

That's the common RS universal output transformer. It'll work just fine but may be too large to fit in smaller battery sets.
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Old 21st Feb 2016, 11:11 pm   #35
gary_crutchley
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Default Re: Vidor CN430 My Lady Anne

Thanks for the advice folks. I intend to check that capacitor, even though it is a silver mica on this set. As soon as I can get a replacement valve I will measure the voltages.
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Old 29th Feb 2016, 10:44 pm   #36
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Default Re: Vidor CN430 My Lady Anne

Hi all,

I received the replacement DAF96 today so I was finally in a position to measure some valve voltages.

First off I checked "that" cap in line with Phil and Keith's advice above. With my DMM on the 20v scale the voltage registered 0V, with the minus sign flicking on and off.

Next I measured the anode and screen voltages on each valve. I had the set on MW and tuned to a quiet area, although there was at least some interference in all areas of the spectrum. The voltage selector was set to 240v, the set was of course on mains and measurements were again with my DMM. The voltages that I measured can be seen in the attached image.

Does anyone want to offer an opinion on these please? Also what further work might be required please?

Regards,

Gary
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Last edited by gary_crutchley; 29th Feb 2016 at 10:49 pm. Reason: Typo and table insert.
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Old 1st Mar 2016, 12:15 am   #37
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Default Re: Vidor CN430 My Lady Anne

Voltages all look reasonable. Given the resistor values for the anode and screen feeds for the DAF96 a cheapo DMM (1Meg) will load the voltage down quite severely, an AVO 8 on 250V range (5 Meg) noticeably and even a decent DMM (10Meg) somewhat.

Worth checking those resistors anyway.
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Old 1st Mar 2016, 10:42 am   #38
gary_crutchley
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Default Re: Vidor CN430 My Lady Anne

Hi Chris,

Thanks for the advice, I thought the voltages looked reasonable but it is good to have the confirmation.

I will check those resistances, then I plan to start cleaning the case. Anyone got any tips for removing nicotine discolouration?

Regards,

Gary
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Old 1st Mar 2016, 2:54 pm   #39
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Default Re: Vidor CN430 My Lady Anne

Hello again all,

I did notice one odd thing when I gave the set a try. If I shut the lid with the power still on I do get the warning tone, however, it seemed to be distorting and there was also a crackle. Operating the volume control a few times clears the crackle.

Is there a dirty switch somewhere or could it be the volume pot? I haven't cleaned the latter as yet.

Regards,

Gary
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Old 1st Mar 2016, 3:04 pm   #40
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Default Re: Vidor CN430 My Lady Anne

After all these years of neglect a bit of switch cleaner on the volume control and the switches wouldn't do any harm.

As Chris said checking the anode and screen resistors on the DAF96 wouldn't go amiss as would replacing the 10n DAF96 screen grid decoupling cap.

Looks like you're nearly finished.

Keith
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