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Old 16th May 2022, 10:55 am   #1
AdrianH
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Default B18T no go project?

I have had a look at a B18T Pye television that I have, the cabinet needs a bit of work, but generally the chassis looked to be unmolested. It is an early set with a serial number of 623189, which is before they all had the AC/DC choke fitted.

I spent a bit of time cleaning it prior to do any tests with the multimeter or applying any voltages. Unfortunately the CRT heater/filament is open circuit.

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So although I can progress a bit further with the chassis I would need a good CRT for the TV.

I was wondering if I could initially try to get it working with a 5FP7 CRT until I realized that had a 600mA heater.

So are there any ideas for an alternative CRT to use that may be a bit easier to get hold of to initially go further with the TV.

One that will not be ready for the Jubilee.

Adrian
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Old 16th May 2022, 11:22 am   #2
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Default Re: B18T no go project?

You can use the 5FP7 with a heater transformer. The EHT will be a bit high but these ex radar tubes seem to take it ok.
Any 9" Mullard tube will be OK with suitable ion trap if required. The MW22-7 has a .6 amp heater requiring a transformer similar to the 5FP7. The Pye B18T performs well but needs a lot of work capacitor wise and the LOPT is a very weak point. They usually fail within two hours of restoration! J.
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Old 16th May 2022, 11:27 am   #3
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Default Re: B18T no go project?

Thanks,

Jeffrey just told me about the transformer idea as well, my brain is not working at the moment probably down to the disappointment over the CRT.

Does the MW22-14 have an ion trap, no mention of one in the Philips data sheet I have?

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Old 16th May 2022, 9:59 pm   #4
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Default Re: B18T no go project?

The only Mullard 9" tube to have an ion trap is the MW22-16. You have to be careful due to the fact that there is very little if any space between the tube mounting and the base to fit an ion trap. For some years Mullard produced the non ion trap tube, the MW 22-18 for these receivers. It was in fact an obsolete tube. Some manufacturers supplied modified tube mountings.
It is very rare to experience an O/C heater in a B18T. J.
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Old 16th May 2022, 10:15 pm   #5
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Default Re: B18T no go project?

Good evening,
Just to make sure the heater continuity is or isn't ok, it is worth giving the pins a good clean first to make sure of good contact. If this is ok but still showing O/C try with a megger to see if there is an intermittent contact.

There is a way to temporarily repair the heater using the high voltage, high energy pulses from the top of the line output valve anode. One side of heater is connected to chassis, the other to a well insulated probe. With the LOPT stage running touch the probe to the LOPT output valve anode until there is some sounds of stress from the LOPT. Hopefully an arc has occurred between the broken ends of the heater and fused the 2 ends back together again.

I did this trick with an O/C heater in a PENDD4021 valve in a pre-war Murphy radio set. It lasted long enough to get the set working and the chassis restored before finding a replacement.

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Old 16th May 2022, 11:19 pm   #6
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Default Re: B18T no go project?

The heater is definitely OC, I have scrapped the heater pins clean and cannot get any resistance between the pins. The tests with a multi-meter were the firsts tests I was doing with the tube, I was planning to test it's emission before I went further, but did not get to that stage.

I have got the tube out of the chassis now, without damage I hope to the scan coils.

I can continue, look at the caps, replace the waxies and smoothing cans, fit the 5FP7 and run with that for a while, as 5FP7 will go up to 7KV EHT.
But I am left with a dilemma, I still have the Ferguson 991 and I do not use that so wondering why I feel the need to get this Pye going. For the money it cost me I could well just take the valves out of it keep them in a box and offer the cabinet and chassis to anyone that wants parts FOC for collection. There are sets on Ebay not working for more than I paid for this one, so there is no financial loss to me.

It is not knowing what to do with it, could I get a good CRT or another bad one, would it be of benefit to use mine for parts if someone has need for parts for their own?

Adrian
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Old 17th May 2022, 6:50 am   #7
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Default Re: B18T no go project?

Did you try to weld the filament? The tube is anyway bad.

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Old 17th May 2022, 7:21 am   #8
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Default Re: B18T no go project?

No I have not tried it, the TV is not running as it stands, so no ready available EHT output to try it with.

Not sure if I would like to use the Ferguson for it.

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Old 17th May 2022, 1:45 pm   #9
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Default Re: B18T no go project?

I have successfully used the line output from one of my Ekco sets to weld the heater on a GEC set, took several attempts whilst tapping the neck to get it going.
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