Repairing a Vidor CN359 - someone who's never done this before

[andrewferguson]

Several years ago I picked up a Vidor CN359 from the side of the road. For some reason I was really attracted to the design of it - and the fact that it is considerably more compact than some others I've seen helps. I got it home and, in typical impatient fashion, tried plugging it in without opening it up first. I got the rather typical "loud hum", which I now believe indicates that the filter capacitors need replacing. Not knowing that at the time, I left it on for about half an hour in the hope that it might fix itself. Unsurprisingly, it didn't, so it was relegated to the shed, where it has sat for several years.

I'm now (slightly) more knowledgeable about electronics than I was back then, and am quite keen to try and attempt a repair. A while ago I searched for schematics and, failing to find any that could be downloaded for free, bought an electronic copy. [Sidenote: is it acceptable etiquette to share these here? I'm afraid that I'll have difficulty understanding them without the help of others!].

I opened up the radio today and took some photos [Uploaded to Imgur due to forum file-size limitations]. I also noted down the models of the valves, or at least all the lettering that I could see. RadioMuseum.org indicates that there are six valves, I could only access four of these:

• U50 Qsram BVA foreign
• Mullard EL33
• Mullard EBC33 BVA
• VR100 10E/278

The two Mullard's match what RadioMuseum.org says should be there, but the other two are different. Is this a sign that "It's been got at!"?

Perhaps the most pressing issue, however, is that my (very) limited knowledge means I don't know which capacitor(s) are the filter capacitors. A skim through some videos online indicates that they're normally the largest, and in a circular "tin-can" style container. I couldn't see anything like that, except for something behind the transformer which I've tried to take a photo of (the photo came out very badly).

I realise that this is a long and rambly post - and it clearly demonstrates my limited knowledge of valve radios. Having said that, I'd love to learn more, and be keen to try and get this to work.

[HamishBoxer]

That sounds right and there maybe variations. Proceed with care, no mains at this time and feel free to ask us. There are certain capacitors need changing/checking.There might be a circuit at the top of this page.

One model same as this or export has 6 valves inc rectifier and magic eye.

[paulsherwin]

You can upload images of any size. The forum software will resize them if necessary.

Your circled component may well be the reservoir and smoothing capacitor, though it's difficult to be sure from the photo. It will probably be an aluminium cylinder about an inch and a half wide and 2-3 inches long. I don't have any service info for this radio so can't give specific advice.

Some of the valves have been replaced at some stage, which is normal. However, the use of a VR100 military surplus valve suggests it may have been changed by an amateur rather than a professional repairer. The VR100 has probably replaced an EF39.

[andrewferguson]

Many thanks for all the replies. I guess(?) the first stage would be to carefully extract the chassis out of the cabinet so that I can get better access to the components.

I used Imgur for the images simple because it allows higher quality (I thought that by limiting the resolution to 800 by 600 would limit the usefulness of the pictures), but for those that do not like external image sites I have attached the three images that I mentioned in the first post to this post.

[Nuvistor]

Quite possibly a Radio Spares reservoir/smoothing, I think they used red letters on their cans.

[HamishBoxer]

Certainly is RadioSpares.I did not see it first time.

[paulsherwin]

It does look like a Radiospares part. Sometimes people made quite a crude repair when the original smoothers failed, lashing the replacement electrolytic somewhere above the chassis with tape or cable ties.

Modern electrolytics are much smaller and can be hidden out of the way underneath the chassis.

[Mike. Watterson]

I see about 7 paper dielectric caps that need replaced. They kill output valves, transformers, rectifiers and the gain.

These are quite rare. I've been collecting Vidor for years and I'm not sure I've even seen one!
https://www.radiomuseum.org/r/vidor_cn359.html

Reminds me a little of the bush SW45 (which I do have). I think the Vidor is prettier and about 10 years later. An era where repairs using war surplus parts was very common.

I worry about smoothing caps last!

[andrewferguson]

I've now sat the radio so it's upright again, but balanced on two pieces of wood so that I can access the screws underneath and remove the chassis.

When removing the chassis, should I be aiming to remove the glass and dial as well, or keep that in the cabinet? In this particular case there are four lights going to the glass dial, as well as the mechanical dial itself. There appears to be around four nuts that hold the glass and dial in place. And should I attempt to remove the loudspeaker or keep it in place and disconnect (cut) the wires?

(I'm sure more experienced repairers would know exactly what to do in this case, but I'm a little nervous of either breaking something or removing something that is difficult/impossible to put back later. This thread will no doubt become filled with posts like this from me!)

[crackle]

The dial frame and pointer operating mechanism in this style of radio is normally attached to the chassis and will come out with it. There may be some screws helping to secure the metal dial frame to the front of the cabinet. The actual "dial glass" may sometimes be fixed separately to the cabinet and remain in the cabinet when the chassis is slid backwards.
There may be enough cable on the speaker to leave it in the cabinet, but I normally remove the speaker once the chassis has been taken out, and place it on the bench so the cabinet can be put to one side. There should be no need to cut the wires to the speaker, unless you intend to replace them. Unsoldering the wires from the speaker transformer tags is a better option, if you do cut or unsolder them them make a note of where each goes.
The speaker must be connected when you operate the radio.

Mike

[Mike. Watterson]

I unsolder the wires at the speaker and extend with croc clip cables unless the cabinet needs work. Sometimes I unbolt speaker and leave it connected, as Mike says, sometimes the wires are long enough.

As Mike says, it's rare that the glass has to be removed (unless blow torching inside of cabinet to kill worms (grubs and eggs really). The back plate with moving pointer should be part of the chassis. Some insane philips and HMV are only exceptions I've met.

Only dust inside of glass VERY lightly with soft dry thing as otherwise paint/lettering falls off!

[andrewferguson]

I have now managed to take the chassis out of the cabinet, and it was surprisingly easy. I removed the four screws on the underside and that was basically it. The chassis - including the dial and glass - just slid out. All that was left to do was to remove a couple of nuts to remove the speaker.

I've now got a much better view of the components in the radio. There are six valves in total, although they don't all match the schematic:

• U50 rectifier
• Mullard EL33
• Mullard EBC33 BVA
• VR100 10E/278
• EM34
• Mullard ECH35

R-type.org indicates that the 5Z4G is "sensibly equivalent" to the U50, and therefore by elimination I can only assume that the VR100 is a replacement for the EF39 (as Paul suggested).


And to those that suggested that the "tin-can"-like device at the back was RadioSpares, you are absolutely correct. Specifically, it bills itself as:

RADIOSPARES
16 - 32 MFD. 450V.
YELLOW 16 MFD. +; RED 32 MFD. +
BLACK AND CAN COMMON NEG.
Made in England

So, now that I've got everything out I'm a bit stumped as to what to do next. Mike, you suggested to start with the paper capacitors first and then go to the smoothing capacitors, so should I just start by identifying them? Apart from the capacitor values themselves, is there anything in particular I should be looking for in replacements?

This may get a bit silly if I (the inexperienced person) am the only one with the schematic and data sheet. What are the Mod's thoughts on me uploading the (paid-for) PDF schematic to this thread? Alternatively I could send it by PM if that is better?

[Nuvistor]

Replacements for most of the paper capacitors these are suitable, use the same or a higher voltage working type. Other suppliers available.
https://www.cricklewoodelectronics.c...-to-1000V.html

Any capacitors that are across the mains 230VAC need to be X type, any connecting to external ports( aerial earth etc) if required need to be Y types.

[Mike. Watterson]

Metalised polyester, 300V rating or more. Actually many parts might be OK at 250V, but I don't know what the HT is without looking at the service info.
A capacitor on the audio transformer primary (if fitted), will also connect to the EL33. It can be 1000V ceramic.
Any capacitor across the mains wants to be X rated.
Replace one at a time. Cut leads near body as new parts might have short leads intended for a PCB.
Also values are not too critical:
0.2 = 0.22
0.15 = 0.15 or 0.22 unless in a tone control circuit.
0.04 = 0.039 or 0.047
0.05 = 0.047
or other powers of ten.
1000pF = 1nF = 1000uuF = 0.001uF

Flat capacitors are usually Silver mica and OK on UK sets.
Mostly the paper caps are 1000pF to 0.5uF. Very occasionally some 470pF / 500pF are paper.
The paper dielectric caps can be in waxed card cases, moulded cases (brown or black and crumbling is common) or metal with a rubber bung each end (which might be red and black, but not polarised, the case might connect to black end).

Electroylic capacitors are 1uF to 500uF (8uF to 100uF is common) and polarised. I test for "reforming" by removing all valves and make sure unplugged and using 30V bench PSU limited to 5mA. You can use a 12V supply and 2 K resistor if you have nothing else.
If the bung is dozy or crusty, then likely they have dried out. YOu can leave the - connected.

Any electrolytics on cathodes have a resistor across them. If leaky, the valve will run too hot and damage can result, if dried out, then the gain is poor.

The paper caps between anodes and grids leaking (and they only had a 10 year expected life THEN) cause the 2nd valve to pass too much current. Can burn out valve, audio transformer, cause hum by loading HT, damage rectifier (U50) or mains transformers.
Leaky paper caps on the g2 pins don't break anything but dramatically reduce the gain.

Most of my Vidor models are battery, but the later Mains only model works great. https://www.radiomuseum.org/r/vidor_cn417.html It's the only "mains only" Vidor I have. Not all my Vidor sets are on my Radio museum page.

Electrolytics can be 10uF for 8uF, 4.7uF for 4uF, a 25uF can be 22uF or 33uF, especially on a cathode.

It should be a good performer when it's sorted.

[crackle]

Is the schematic you are using the R&TVS one (labelled Radio Servicing at the top) obtained from Paul's site?
I would think most people who are in a position to help probably have a copy on the very useful DVD Paul sells.
It is normally OK to include parts of the schematic in a post to illustrate what you are talking about, for instance if you are talking about a problem with the output then just include from the final IF stage to the power supply. But I dont think they like the whole schematic to be added.
Mike

[Sideband]

Originally Posted by andrewferguson

What are the Mod's thoughts on me uploading the (paid-for) PDF schematic to this thread? Alternatively I could send it by PM if that is better?

As far as I am aware, the mods are ok with posting circuits or parts of as long as they are not available for purchase via the forum (top right panel). You can't send attachments by PM but you can (if it IS ok with the mods) attach a PDF to a normal forum post.

[Herald1360]

If the schematic's "up top" then you may not upload other than snippets- these sales help finance the forum. Otherwise fair game, though some sources may disagree. You may need to edit out watermarks or other traceable source indications!

[Station X]

If in doubt check the forum rules:-

8.Do not post or request service data, or links to service data, if it is for sale at www.service-data.com. The service data website funds this forum. You may post a small section from published data (such as a section from a circuit diagram or other diagram) to illustrate or help with a discussion.

[Mike. Watterson]

I think the CN349 and CN359 are very similar and also called "Chanson".
The export versions (probably a SW replacing LW) are CN354, CN363 and CN367.
I'm thinking I've only even seen actual photos of the CN349, not the CN359.

The closest I've seen to a photo is this advert:


Edit: Never seen those other two models either.

[Mike. Watterson]

I checked the Trader Sheet index, the CN349 is on it but not the CN359. The CN359 is page 422, Vol II R&TVS, maybe 1953 edition only. I have all the R&TVS books up to 1975-76, so can refer to that.

Best only to post snippets of anything either sold here at all, or if from Radio Museum.

Probably paper needing replaced
All 100nF / 0.1uF: i.e. C6, C11, C13, C27, C37. The C37 is the one that causes most damage.
All 10nF / 0.01uF: C30 C33
1nF / 1000pF / 0.001uF: C32
2nF / 2000pF / 0.002uF: C38, use 2.2nF or 2nF 1kV Ceramic. It's the Tone Corrector / Snubber.
50nF = 47nF (0.05 uF): C40 needs 550V or more rating, HT + audio voltage peak! Treble cut tone control.

Check C36. If it's NOT a flat type (mica = OK) but round, then replace with 470pF or 560pF.

Electrolitics
C34: 4uF, can be up to 10uF, 300V. Preamp HT decoupling/smoothing.
C39: 50uF, can be 47uF to 100uF, not critical, but 15V is minimum, I'd put 25V. Cathode Decoupling, increases gain. Sounds good if dried out, damages valve etc if leaking.
C41, C42: Main smoothing. 350V, using 450V is fine. C41 should be 15uF to 16uF, no larger to avoid stressing V6 rectifier. C42: 24uF can be 22uF to 47uF at 350V or more.

Resistors can be +/- 25% and it won't make much difference. I only test them if everything else is OK and radio is still poor.

Maybe R25 is the only really critical resistor as it has main cathode current and sets EL33 bias.

R1 & R2 actually set RF & IF basic gain, 100k & 33K, should be OK. It tends to be resistors over 390K go high and less than 1K with power, going low that are the only resistor issues in general in valve radios and amps

C6 is screen grid decoupling. If they are leaky there is poor or no gain.
C11 and C27 likely have little effect if slightly leaky as they are on cathodes, so less than 12V. RF decoupling.
C18 is AGC, if leaky, then gain may be at maximum all the time.

I think all the other caps are likely silver mica and thus OK. It's only certain USA pre WWII models that have Silver Mica Disease and only where there is high voltage across them. Sometimes they can be physically damaged.

Always look for burnt, cracked, loose, poorly soldered parts.



No X caps on mains.