Defiant 7109

Well done for clearing this matter up Chris  and I stand corrected  ? I was very much mistaken and apologies to all. As I mentioned above, its been a number of years since I dabbled in B&W and clearly have forgotten many things. That data and my stock also had me well and truly mistaken ?   Shame none of this helps Andrew I have spare B&W tubes in the loft but not of this type, I will check though just in case I forgotten that correctly too. ? 

CME1703 is a 110 degree CRT.

Something in the back of my mind thinks there was a CRT type that used an ion trap magnet similar to the ring just forward of the CRT base and used a straight gun. Not certain though, I will have a search later today.

Most of the sets I saw were post 1959 with 110 degree CRT’s so not a lot of experience with these types, or if I had I have forgotten. 

Some info on CRT’s, one USA type with a straight gun and built in ION trap and the Brimar C17AA/Mullard A43-88 with a ring type magnet to align the beam, unfortunately I cannot find out if the gun was straight on bent.

Thanks for the input chap's, here are some more pic's of the CRT under test and of the gun assembly. The focus is set for optimum, but the CRT is certainly well past it's best.

Is it worth trying a boost transformer if you can get one? Will the CRT tester give the heater a 25% boost like a boost transformer and test it under those conditions. The transformer used to get 6-9 months extra, with the amount of use the TV will get it should last a long time.

Of course the caveat is it doesn’t always work.

I think I'm flogging a dead horse as since earlier, the emission is falling away back to as it was before. It won't even register on the B&K plus the picture is worse. Barely visible in a darkened room. Increasing the heater volts makes only a slight improvement.

There is no alternative, a replacement CRT really is needed for this set.

Fair enough Andrew, only so much material on the cathode, has the supermarket says, “When it’s gone it’s gone”

If only there was a way of getting cathode material re-applied.... Deep sigh...  ? 

Anyway, are we all agreed that this CRT is a Mazda CME 1702 ?

I'm really pleased with the set and it is certainly a worthwhile restoration, despite said CRT being poor.

I wonder what is happening over at the ETF over in the states and their rebuilding project with the equipment from RACS and Hawkeye? Doesn't seem to be any updates since their first successful rebuild back in 2016 and a metal cone CRT at that ?.

I could imagine the costs involved getting a CRT transported to and from the U.S.A. and regunned could be rather prohibitive.

Wouldn’t like to think what this company charge.

https://www.thomaselectronics.com/manufacturers/#about_thomas

As a matter of interest, soon after my last post I decided to give the CRT another wallop. This time, I increased the heater volts to 14 and left it for a few moments longer on the rejuvenate function to allow the cathode to get nice and hot. I then hit the button and got a healthy kick from the meter. The CRT now reads just out of the bad section and the picture is pretty darn good indeed. Now, it has remained stable for about two hours, so lets see how it goes over time. Could there be life in the old girl yet?

That doesn't look bad Andrew, I'm very surprised that CRT came up at all looking back at your previous posts. Even if it's short lived you have well and truly proved the chassis is a good'un.

PS. I guess you don't need the B&K wiring codes since you found adaptor 10  ? 

Hi Marc, yes the set is good, ok the CRT may or may not live much longer....we'll see. I think if it were a cat, it could be on it's ninth life. I took the view that if it were duff anyway, a good blast from the B&K could be worth another try.

Thanks for the offer of a wiring diagram, but the base number 10 must be right.. ? 

The chassis still has many wax capacitors, only the very leaky brown Wima type have been changed so far. The results are excellent, as can be seen above.

So far the CRT has remained stable as far as emission goes. I'm not expecting a miracle, and would not be surprised if it deteriorates...but it sure is way better at the moment than it was before.

So far, I have not paid much attention to the sound. It is there, but lower than it should be with excessive vision on sound coupled with poor (very critical) tuning. I have set up the local oscillator in each channel of the tuner, but it is clear that at some distant time in the past the IF coils have been twiddled. Several of the hexagonal cores are cracked and damaged. Oh what joy. This is a real pain as I have no replacements. Not only that, it is of course very difficult to remove fractured cores.

Hi Andrew,

That looks like a good picture after giving it an extra bop! Hopefully it will last.

Thanks Jon, yes it will be great if it holds out.

Taking a look at perhaps why the sound was none too hot, this hastily fitted capacitor (below pic) turned out to be a wrong value of 0.001uf. It was a replacement for c53/54, both 0.003uf on the cathode of V9, the old ceramic ones still being there but broken in two. Not only that, an additional capacitor of 0.1uf had been fitted across c49 (should only be 0.002uf). R61 had previously burnt out and I replaced it too. ( A 1.2k feeding HT to the screen of V9). Correcting this brought about an increase in sound to normal levels.

The excessive heat has caused me to temporarily abandon the workshop....it is unbearable this afternoon.

My workshop (garage conversion) is the coolest room in the house in summer and the warmest in winter, all that celotex paid off. During this heatwave I've been seeking sanctuary in there. I kid you not, at the height of the day I have to pass through the conservatory whose thermometer is frequently off scale( which is 100F and can hardly breathe out there), to gain access the parts storeroom which sits at about 80F. Then through another door in the storeroom to the workshop which is at a comfortable 65F and a fair bit lower in the evening.

Wish I had air conditioning in mine....and the rest of the house too. However, the resulting electric bill might not be so attractive.  ?