Vidor CN429 Help wanted

[slidertogrid]

C6 tests as 121 pf should be 100pf C7 532pf should be 540pf. I have tested the DK96 in another set and tried the DK96 from that working set in this one.
I tightened the valve holder grips up with a needle and gave them a scrape such as I could but hopefully in this picture attached it can be seen where the valve pin is connecting with the grips, I think it's only the ends that are a little dull and tarnished where the grip splays out.

Then I took a look at the cores in the I.F transformers and compared them to my unrestored set. The ones in this set are lower one is very low compared with the unrestored set... So maybe it's been twiddled? Should I try putting the cores into the same position to the unrestored set? Unless of course the unrestored set has been twiddled..?

Picture 1 is the unrestored set (wax capacitors still in place) Picture 2 and 3 are the set I am working on. The cores are lower in fact one cannot be seen. it is there though as I used a bit of wire as a probe.
Rich

[slidertogrid]

Some success . I decided that I had little to lose so I wound the upper slugs to about the same position as the other set, One slug was miles out. I then had Gold coming in fairly loud. I checked the bottom slugs they too had been twiddled. I then rocked the slugs backwards and forwards for best reception.
After a bit of playing around I now have stations on MW where they should be with good volume. Even L5-L6 had been twiddled!

The problems I have now is that it still bursts into oscillation around 500m and stops around 540.
Long wave only picks up radio 4 right at one end of the dial but with good volume. Nothing else on LW at all.
The core of L5 - L6 has to be a bit further out for best reception than it is on the unrestored set.
TC3 seems to work as it alters the tuning and the position of the station being received but TC1 does nothing on either waveband.

Maybe this is the original fault and why the cores were played around with?
Without a signal generator etc I don't suppose I am going to get this much better?
Many thanks to all who offered help and encouragement it is very much appreciated!
Rich.

[Herald1360]

The set looks to be quite heavily cost engineered with only one oscillator coil and a sketchy set of trimmer and padder capacitors giving little leeway for alignment. It's likely that unless the IF is set precisely to 470 kc/s, the rest of the alignment will be all over the place since it relies on one fixed padding capacitor (C6) for oscillator tracking on both LW and MW and there are no tracking (padding) trimmer capacitors in the aerial circuits at all.


This may explain the "way out" location of Radio 4 on long wave. It would seem likely that at best, the LW tuning would be a compromise, with only "Droitwich" lined up with any accuracy!


Good fun if the phantom twiddler has had a go at the IFTs and you haven't an accurate sig gen for IF alignment!

[cathoderay57]

Ok it seems the oscillator was running after all! Well done for getting it working thus far. An accurate alignment is going to be hard to do without a sig gen. TC1 is only intended to work as a LW trimmer. C7 is listed in the Trader Sheet #1153 as C6 (as mentioned by Herald - we crossed in the post) and given a value of 532pF so yours is spot on. That's important because this capacitor is the tracker which determines MW tuning scale accuracy. Can you say whereabouts on the tuning scale you are getting Gold, as well as the expected scale point from another set? I'm assuming that Gold is at the shorter wavelength end of the MW band. You might be able to address the oscillation at the other end of the band (500m) by a careful tweak of L5/L6 core. L5/L6 should be adjusted at the longer wavelength end of MW band and TC3 at the shorter wavelength end. If you cannot bring the scale into alignment using these 2 adjustments it probably means the IF frequency is out so you ought to use a sig gen for that at 470kHz. Cheers, Jerry

[Phil G4SPZ]

You can get by on many repairs without a signal generator, but it looks like you have reached the point where you can't progress any further on this set without one! I have something surplus to requirements that might be suitable - drop me a PM if interested.

[slidertogrid]

Thanks for the offer Phil PM sent.
I am going to have another look later today and see if I can improve the alignment at all further with a careful tweak.
It beats me why some people twiddle IF transformers... what do they think ?
I remember donkey's years ago when I had my shop taking in a transistor set for repair, When I asked what was wrong the owner said it had stopped working after he had tightened all the screws...Over the years I recon I had them all.. WD40 in the video because it squeaked. Mains dropper on a 3500 replaced with a bit of electric fire element...
The best was a bloke who had intermittent colours changing on an early widescreen set that was just out of guarantee he decided to tighten up the picture valve by twisting the panel on it. The set hissed and now the picture valve was full of sparks and he had no picture at all.... Had he let the gas out? had I got any gas and could I show him where to put it?

Rich

[Phil G4SPZ]

Hi Rich,

You have two PMs regarding signal generator and postage.