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Murphy V310A Number Two.

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PYE625
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I have re-stuffed the two capacitors under the brightness/contrast controls, and as before, simply have to moan about how awkward it was. This is mainly because I'm paranoid about tipping up the chassis due to the can of oil, so worked on it in the upright position..... sort of.   ? 

Before....

IMG 4004 50

After....(Drat, I have one the wrong way around....instant dismissal from Murphy for that.)

IMG 4008 50

Overview of chassis before I re-fit the CRT....

IMG 4006 50

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 17/03/2018 10:54 am
Nuvistor
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Can’t get over how clean and bright it is after 60 years, even the red label on the rectifier has not fallen off.

Wait with anticipation for first light. ? 

Frank

 
Posted : 17/03/2018 11:28 am
PYE625
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That could be a little while off yet Frank.

I have fitted the CRT and all seemed well with sound but no vision. There is no EHT despite line whistle and a good spark at the U26 top cap. The heater of the U26 is lit, so what could be the reason? Furthermore, a faint blue glow can be seen in the U26 plus another new one I tried.

Well, the EHT is being dragged down as there is 11 meg's. dc resistance between the U26 heater winding and ground. This can only mean an insulation breakdown inside the LOPT can. Using another EHT lead with a stick rectifier diode produces a raster, so it is more or less confirmed.

Question is, do I use the LOPT from the other set or open up this can and investigate? Or simply use a stick rectifier in place of the U26?

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 17/03/2018 3:27 pm
PYE625
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I have decided to neatly install a suitable solid state rectifier within sleeving in series with the EHT cable from the U26 top cap lead out of the LOPT can.

I do not like the idea of ruining the LOPT can without the means to return it to the condition it is in now. It works well with the above arrangement and so to me, pointless to open it up.

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 17/03/2018 4:34 pm
PYE625
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Here is the result, I have also continued the sleeving of the EHT lead through the chassis. Not as pretty as the U26, but much less ugly than a cut-open LOPT can. I'll leave the U26 holder in place for when a nice NOS Murphy V310 LOPT becomes available..... but I better not hold my breath !   ? 

IMG 4012 50
IMG 4013 50

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 17/03/2018 5:18 pm
Nuvistor
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And we had high hopes for that LOPTX, just shows there is always something to catch us out.

Just watching the snow on the CCTV , doesn’t look like it is sticking on the ground at the moment.

 

Frank

 
Posted : 17/03/2018 6:34 pm
Katie Bush
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That's a pity, but at least it remains functional. Better to do as little destructive work as possible, and the net result is the same, than to make a big ugly scar all the way around the can.

So, does all this feverish work mean that we'll be seeing pictures by Sunday tea-time?

 
Posted : 17/03/2018 7:55 pm
PYE625
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Not quite I'm afraid. Although a faint raster is visible, the CRT is totally flat. Game over once again unfortunately.

IMG 4019 50

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 18/03/2018 9:37 pm
crustytv
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You have a B&K give it a bop, you may be pleasantly surprised. Nothing to lose.

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Posted : 18/03/2018 9:39 pm
Marc
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Oh no, not another CRT  ☹️ 

I thought you might have tried your B&K on it.

EDIT....Oops crossed posts with Chris.

Marc
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Posted : 18/03/2018 9:43 pm
Katie Bush
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Ah Blitzen....

Or, you could let it run a while, and see what happens, but do you know what? I'd have had that B&K on there before I started!

 
Posted : 18/03/2018 9:43 pm
PYE625
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Hi Chris, I have no suitable base to fit this tube and it's not listed (CRM172).

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 18/03/2018 9:46 pm
crustytv
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Posted by: Katie Bush

I'd have had that B&K on there before I started!

Agreed, that's always my approach too before investing too much time, effort and components on a set.

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Posted : 18/03/2018 9:46 pm
crustytv
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Posted by: PYE625

Hi Chris, I have no suitable base to fit this tube and it's not listed (CRM172).

Once you find the pin-outs of the CRM172 just use croc clips, I've done that before adapters are a luxury but not essential.

croc
bk467

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Posted : 18/03/2018 9:47 pm
PYE625
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Thanks Chris, I'll give it a go one evening, but something tells me that as this tube is a triode, it won't be suitable for the B&K ?  

In fact what I have done just now was to connect up my capacitor reformer to the grid of the tube and attempted to measure any cathode current. There was not a sausage, even with the heater voltage slightly raised.

Perhaps this thread should be renamed " The Murphy Curse"..... Part II.

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 18/03/2018 10:03 pm
Katie Bush
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My Mullard data book doesn't offer a Mullard equivalent, and the only other equivalent I can find is 7404A.

If the B&K setup data includes that, then you're in business, if not, it looks a bit like you're on your own for the moment.

 
Posted : 18/03/2018 10:26 pm
ntscuser
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Posted by: PYE625

 

Perhaps this thread should be renamed " The Murphy Curse"..... Part II.

"Murphy's Law"?

Classic TV Theme Tunes

 
Posted : 18/03/2018 11:04 pm
Doz
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I can offer the loan of my Leader if you wish to attempt to bop the tube a bit ...

 
Posted : 19/03/2018 3:09 pm
Katie Bush
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A little bit of an update from lastnight...............

To recap, the Mullard equivalents list (1964-65) shows the 7404A (who made those?) as an equivalent to CRM172.

A little further digging reveals this....

GEC 7404A (Custom)

Looks like a tetrode to me..... It's the CRT in my GEC BT2155, and was tested by Marc on his B&K about three years ago. It was tested on the same settings as a Mullard MW43-80. The Mullard is  90* scan, versus the 70* scan on the 7404A, so that doesn't affect the test. Oh, and it tested very good indeed!!

So there you go, before bopping etc, try testing it as a Mullard MW43-80 and see where it stands before doing anything else. Just be mindful of the heater volts. I'm pretty certain it's 6.3V, but I may be fuddling it up with another 70* CRT that I have which is 12.6V.

>>>EDIT<<<

You can also see the pin outs on the picture above, so even without the correct base, you can use Chris' 'fly lead' approach if you wish.

 
Posted : 19/03/2018 3:39 pm
crustytv
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Posted by: Katie Bush

[...] shows the 7404A (who made those?) 

 

Brimar

Posted by: Katie Bush

Looks like a tetrode to me.....

It is

crm172

 

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Posted : 19/03/2018 4:29 pm
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