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Murphy V310A Number Two.

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Katie Bush
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Right, so that's that sorted! And I guess I was befuddled with the heater volts.

So, it basically tests the same as the MW43-80 but with a 12.6V heater.

 
Posted : 19/03/2018 4:36 pm
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Katie Bush
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And there's a point...... Are the heater volts up to scratch?

 
Posted : 19/03/2018 4:58 pm
Cathovisor
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The issue with the CRM172 is that, as has been mentioned before, it has a neck diameter of 35mm whereas the Mullard near-equivalent has a 38mm neck.

 
Posted : 19/03/2018 5:05 pm
PYE625
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And there's me getting mixed up with a triode and a tetrode.... ? 

The heater voltage in the set is correct at 12.6 (ish) volts. 

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

 
Posted : 19/03/2018 5:07 pm
PYE625
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Posted by: Doz

I can offer the loan of my Leader if you wish to attempt to bop the tube a bit ...

Thanks Doz for that kind offer, I'll have a go with making up leads first as mentioned above, but I think the CRT is beyond hope. We'll see.

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

 
Posted : 19/03/2018 5:11 pm
PYE625
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Erm yes....leads will not be needed as the AW43-80 base fits quite well it would seem. Surprising that.

IMG 4021 50
IMG 4020 50

Unfortunately, no reading whatsoever can be achieved and even after a full bop, a big fat zero. All manipulation of the drive controls yield nothing. This tube is dead. Flat as a pancake in a 10,000 tonne press.

IMG 4023 50

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

 
Posted : 19/03/2018 5:48 pm
PYE625
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But it was fun getting the chassis up and running, I did enjoy that even though the results are negative.

It goes to prove that just because a set looks to have had little use and is all nice and clean, it don't mean a thing. I was wrong to just assume the CRT would be great. Oh well, can't win 'em all !   ? 

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

 
Posted : 19/03/2018 5:53 pm
PYE625
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So the tale of two Murphy's will come to a temporary stop until another CRT can be sourced. All in good time, as one is bound to show one way or another.

Third time lucky perhaps?  

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

 
Posted : 19/03/2018 6:22 pm
crustytv
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Out of interest how does the emission fair when you raise the heater volts to 14.6V-15.6V

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Posted : 19/03/2018 6:35 pm
Cathovisor
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I'm wondering if Andrew's tube is suffering from what previous Mazda CRTs I have encountered have - a disconnected cathode. It might be interesting, solely in the name of science, to see if via experiment a current can be drawn between grid and first anode.

 
Posted : 19/03/2018 6:40 pm
PYE625
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Hi Mike and Chris, well there is nothing with elevated heater volts and I did previously use my cap reformer to test for anything between the other electrodes, again nothing.

I wouldn't be at all surprised if it has been boosted before and is now suffering a stripped cathode.

I'll just nip over to the local tube re-gunner's for a quote......  Time machine anyone?   ? 

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

 
Posted : 19/03/2018 6:48 pm
Katie Bush
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Ah, Hell............. That's a pity, but if it's truly that flat, where does it get enough emission to show that raster? No matter how dim, there are electrons coming from somewhere!

Now then, remind me of that procedure to produce an image of the cathode surface on the CRT screen? - could be worth a try, even if only to prove there is either, no cathode emissive surface left, or an O/C electrode?

 
Posted : 19/03/2018 7:00 pm
crustytv
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Posted by: Katie Bush

Now then, remind me of that procedure to produce an image of the cathode surface on the CRT screen? 

I could be wrong but isn't it a case of removing the HT (A1) and leaving just the heater and final anode? Maybe you have to also drop the EHT a little. I'm sure we covered this on Vrat 1.0

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Posted : 19/03/2018 7:30 pm
Katie Bush
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Hi Chris,

To be honest, I've never even seen done, but I've heard plenty of guys who have mentioned it, and likewise, I think it has been covered in the past, though I don't recall how it's done - maybe someone with more historical experience can enlighten us?

 
Posted : 19/03/2018 7:43 pm
PYE625
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There is obviously some very minimal emission, but how anyone could have watched this in the "dim" and distant past, I'll never know !   ? 

Naturally, all voltages and video drive to the tube have been checked. Perhaps not quite the picture that would sell a Murphy. ? 

IMG 4024 50

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

 
Posted : 19/03/2018 7:52 pm
Nuvistor
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It does look like an OC cathode, try a slight tap on the CRT neck, not too hard, don't want to hear a hissing sound.

 

Frank

 
Posted : 19/03/2018 8:02 pm
Katie Bush
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Posted by: PYE625

There is obviously some very minimal emission, but how anyone could have watched this in the "dim" and distant past, I'll never know !   ? 

Naturally, all voltages and video drive to the tube have been checked.

 

Well, straight off the bat, that looks way better than lastnight's photo - not saying it's good, but better. You can clearly see it's a testcard this time! How about letting it run? So often we hear of CRTs improving as they run, and afterall, what's to lose?

 
Posted : 19/03/2018 8:02 pm
PYE625
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Posted by: Nuvistor

It does look like an OC cathode, try a slight tap on the cut neck, not too hard, don't want to hear a hissing sound.

 

I heard that sound a while back with the first set.... and that was a very good tube.  ?  ?

Let's change the subject before I cut my neck !   ? 

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

 
Posted : 19/03/2018 8:06 pm
Katie Bush
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Posted by: Nuvistor

It does look like an OC cathode, try a slight tap on the cut neck, not too hard, don't want to hear a hissing sound.

 

I was thinking along those lines too, but not so much to find an O/C electrode. A nice young man I once knew (Ralph) showed me his party piece, gently tapping the neck of the CRT with the set switched on, brightness and contrast at maximum - I was amazed to see the screen become gradually brighter as he tapped. He reckoned it was almost as good as bopping, but less destructive.

However, by the same token, I also had an early 90's Sony, one of the ones 'known' to suffer bad welds on the internal electrode connections (according to Mr Ted, of Ted's TV in Selby). A tap on the neck brought pictures back to the screen - for about an hour, then off it went again - definitely a dud!

 
Posted : 19/03/2018 8:14 pm
Nuvistor
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Any chance of a dry joint on the CRT base pins? Live in hope.

 

Frank

 
Posted : 19/03/2018 8:30 pm
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