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Leader LC910A CRT tester..

 
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Leader LC910A CRT tester..

Post by Katie Bush » Thu Feb 05, 2015 12:48 am

Hi all,

I've just taken delivery of the above CRT tester, and have given it whirl tonight by testing a Mullard AW 43-80 mono CRT.. Now that particular CRT has previously been tested with a B&K (model unknown) tester and tested as basically dead, so low emission that it was hard to get a meaningful reading.. However, on this LCT910A, it tests being at the top end of the scale - well into the red zone (about level with the "90" mark on the G1 scale).

It seems improbable to me that the CRT can give such widely differing results on two different testers (one, almost zero, and the other, about 90%).

So, given an unrestored set, which tester is most likely to be correct, if either? And, is it really possible for two different testers to show such a vast discrepancy? (I will disregard the results I obtained with the Muter, last year, on account of it being known to have a fault/or faults).

I suppose, the real question is this... What are the odds of the Leader being faulty? Given that it has not seen any service in a long time, and judging from its overall condition, it has seen very, very, little service in its life.

Could it even be that like vintage TV and radio sets, it needs time for all those electrolytics to reform before it will give reliable results?

Straight out of the box, it shows no signs of wear from service, no scratches or rubbing to the control panel, and even the mains plug is virtually brand new condition (older style 13A without insulated pins), and evidently fitted a very long time ago.. The only real wear is to the outside of the casing (paint spots and paint transfer from other objects).. The tester is complete, as supplied new, with the three standard test looms.. It has its original set up chart (No.7) but no separate instruction manual or schematic diagrams etc.

Marion

 
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Re: Leader LC910A CRT tester..

Post by PYE625 » Thu Feb 05, 2015 10:08 pm

Hi Marion,

It could well be faulty given the widely differing results, however, could the B&K have been giving the wrong readings in the first place ?
All I know is that like valve testers, differing results can be obtained and for example a valve tested "bad" could well still operate with no problem in a given piece of equipment.
On the other hand, valves tested "good" can still not work correctly in a given application.
This is exactly what I used to find when testing KT66 for Quad II amplifiers.
Excessive grid emission leading to thermal runaway was a prime example, even though the valve in question tested 100% in every way.
Testers are good for an approximate guide, but the ultimate test is in the actual circuit the valve/tube will be used.
I'm not saying testers are a waste of time, but the readings cannot always be taken for Gospel truth !

Be very keen to hear what others have experienced :)

 
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Re: Leader LC910A CRT tester..

Post by marc » Thu Feb 05, 2015 10:35 pm

Hi Marion & Andrew,

Marion I'm guessing it's my B&K 467 that I brought along last year. Now I don't know if this will help or hinder but when used on my own mono sets the results have always been about right maybe slightly under reading but not by a lot. If it says bottom red on any CRT's I've had then yes they are pretty much dead and on the best CRT's the reading is high in the green. Any where in between reflect what the meter says and how the CRT looks.
I know some people have had iffy readings from their B&K's but on the whole mine isn't too bad though not perfect.

Marc.

 
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Re: Leader LC910A CRT tester..

Post by Katie Bush » Thu Feb 05, 2015 11:04 pm

Hi Marc,

It was indeed, and have no reason to doubt the B&K, but if I look at it the other way, that means I must have bought a defective tester - so that makes two I have. :ccb

The reading on the the Leader would be quite plausible, if I were testing an unknown CRT, but knowing the tube to be kaput in the first place, and then to get a reading that suggests about 90% emission does make me wonder about this Leader - I guess I need to dig out a "known to be good" CRT and see what that says.. I would guess that it would read "off the scale" at the high end, and if so, would point towards a definite fault on the Leader - Which would be just my luck! :bbd

Now, the trouble is, I've opened up the Leader and can see nothing awry, no sight, sign nor smell of anything having fried, which rather leaves only the electrolytic caps in there (about half a dozen) and my query regarding the need for them to be reformed, bearing in mind that this Leader would seem to have had a life of ease, and just sitting around as a shelf ornament.. There are no complex electronic circuits or "computer control" modules etc, just good, honest hard wired kit.

How would you fancy a CRT 'face-off' between your B&K and this Leader? :aak

I have heard mention of B&K reading low, but the discrepancy here is just too great to write off as the difference between two manufacturer's differing test sets.. Maybe I need someone with another known, good, Leader to 'face-off' against?

Just as a closing thought, I wonder if leaving this tester connected to a CRT in "Test Emission" mode for some time might result in the readings changing (as caps reform?) to something more plausible.

Marion

 
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Re: Leader LC910A CRT tester..

Post by crustytv » Thu Feb 05, 2015 11:31 pm

Hi Marion,

can I ask one thing and no disrespect intended, you state you have tested the CRT but have given no details of how you performed the test. What settings did you use? What did you set G1 too? Did you set the cut-off correctly? Have you checked the right adapter was used? Have you ensured it does not have a flaw in the base adapters wiring? There are many variables other than the tester has a fault.

So before assuming the tester is fault all the above need to be established first. I have two of these and both are in original condition i.e no work carried out whatsoever.

Just like valve testers are not designed for soak testing valves, the CRT tester should not be run for extended periods of time or in this case, to reform electrolytics. Which in my opinion is highly unlikely to be the issue anyway.

Finally the operating manual, schematic and set-up charts were always to be found in the library.

Hope that offer some food for thought

Chris

 
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Re: Leader LC910A CRT tester..

Post by marc » Thu Feb 05, 2015 11:34 pm

Hi Marion,

You could well be right about the caps in the Leader, I wonder if a reform would sort it :aaq
Which makes me think I must get the B&K out and give it a warm up as that hasn't been used for quite some time. In fact maybe I should get in to the habbit of running up all test gear once in a while :aaq

As for a Leader "face off".....calling all Crusty's, calling all Crusty's, come in Crusty :bba

Marc.

EDIT....Crusty has already got there just before my post. :)

 
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Re: Leader LC910A CRT tester..

Post by Katie Bush » Thu Feb 05, 2015 11:50 pm

Hi Chris,

Just for the record, I followed your thread, in which you tested the CRT from the 'Portarama' as a base line guide, and used the set up chart (chart No.7) as supplied with the Leader, and following the guide inside the lid of the case.

CRT - AW 43-80
Adapter - No.1
Heater - 6.3V
H-K leakage - infinitesimal (very, very low - well within permitted tolerance according to instructions)
G1 volts - 45V
"Cut Off" set as per instructions (centred on the scale legend "Set Cut Off")

Switched to "Read Emission" - Result = 90% (on a CRT which previously read about 5% to 7% when tested on Marc's B&K).

I have not made any efforts to use any of the restorative options (e.g. remove shorts or rejuvenate etc).

I did notice that any variation in the above voltage settings (i.e. voltage drop as cabin heater cut in/out) can make a significant, though not massive, difference to the result.

Of course, I can accept the possibility of "pilot error" if my setting up procedure can be shown to be in error.

All plugs, test looms and external wiring is undamaged and in 'as new' condition - no amount of flexing and teasing with the wiring shows any effect.

I'm not implying that there is a fault, just saying that it would be just my sort of luck. :aai

Marion

 
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Re: Leader LC910A CRT tester..

Post by Cathovisor » Fri Feb 06, 2015 12:09 am

Having tried one of my B&Ks on Chris's Decca and finding it u/s, I took it to pieces some time ago (and am yet to reassemble it :ccg ).

What I did find was that there are three 620k 2W resistors in the multiplexer circuit and all three of mine were cooked, with values up to 950k. Why, I have no idea. They've now been replaced (with four 620k 0.75W resistors in series/parallel) and I have checked the waveforms are what they should be - now I just need to put it back together and find a willing guinea pig!

I do have another 467, and a Leader too. Plus my original Radar, of which I still must tidy the scans up for the library here.

Add to this that my Radar 202 is playing daft beggars... :cch

 
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Re: Leader LC910A CRT tester..

Post by crustytv » Fri Feb 06, 2015 8:53 am

Hi Marion,

Katie Bush wrote:Hi Chris,

Just for the record, I followed your thread, in which you tested the CRT from the 'Portarama' as a base line guide, and used the set up chart (chart No.7) as supplied with the Leader, and following the guide inside the lid of the case.

Thanks for the additional info at least we have the test conditions established :thumb

Katie Bush wrote:I did notice that any variation in the above voltage settings (i.e. voltage drop as cabin heater cut in/out) can make a significant, though not massive, difference to the result.

Regarding the variation in test results as your cabin supply voltage varies, this is normal and to be expected.

The +/- variation in supply voltage will result in a slight dip +/- of heater volts and in turn cathode emission readings, which again is normal.

You can simulate this by manually adjusting the heater volts yourself. When using the leader I often do a quick check to see how good a cathode is by simulating a low heater supply, say of around 5V on a 6.3V device.

A good cathode will still give very good emission ( albeit lower than at full htr ) with low heater volts. A tired cathode at this heater voltage will not be so good but at the correct 6.3V, giving acceptable emission. A cathode that is well and truly on its way out when placed on 5V will show virtually no emission but at the 6.3V will give some emission. This is effectively a cathode life test, so as you can see a variable cabin supply no matter how little, will effect the heater volts and in turn will significantly vary your emission readings.

I will say on more than one occasion I have encountered quite significant differences in reported emissions when using the B&K and the Leader, mine were about a 30% difference in FSD. The B&K has been reported by one than one person in the TV communities to be less than truthful on B&W tubes so its not just me being biased towards the Leader.

For example I have a NOS 19" colour tube. When run for 10-15mins ( allowing warm-up and stabilisation) the B&K reports it at about 80- 85% FSD, the leader doing the same gives 95-100%. Life tests on both devices show the cathodes to be in superb condition. More evidence the B&K reports lower emission readings than the two Leaders I own. By the way both Leader report identical results so its not calibration. The 30% variance between Leader results and B&K may be due to how the device test and report results.

Based on that fact the B&K reported your B&W CRT's emission low in the red scale and the leader high in the red scale, I would not trust/rely fully on what the B&K reported.

Katie Bush wrote:CRT has previously been tested with a B&K (model unknown) tester and tested as basically dead, so low emission that it was hard to get a meaningful reading.. However, on this LCT910A, it tests being at the top end of the scale - well into the red zone (about level with the "90" mark on the G1 scale).

The above statement is personally confusing, photos would have helped here. Are you stating the Leader is reporting a much improved emission reading than the B&K but it is still in the red? If so Its not reporting a 90% variance more a 30-40% (of FSD) difference. The variance if you take FSD (which you should) of the meter into account, is what I would expect given my past experience with the two testers. Its not as though the leader is stating the emission is good and reading high or even low in the green portion. I would say it is just reading and reporting the low emission differently than the B&K, which fits in with the many reports that the B&K always reports lower emission even on good tubes.

Anyway none of this helps you, the only way for you to be confident and satisfied is to have another independent known good tester. Whatever the readings if all the above is true i.e. B&K reports low emission ( Meter reads low in red section), the Leader reports better emission ( Meter reads higher in red section), the CRT is low emission. Both CRT tester agree on that, all we are really debating is how low. Out of interest how did the needle behave when you set the G1 and cut-off was it a smooth reaction or did the needle jump about a bit.

I may be going out on a limb here but I would venture to say your leader is probably working OK.

 
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Re: Leader LC910A CRT tester..

Post by Niall » Fri Feb 06, 2015 12:19 pm

This is a calibration issue. Are there no extant setup / calibration instructions for these instruments?

It is always a good idea before embarking on a serious measurement exercise to carry out at least a basic "sanity check" on the instruments to be used against some sort of known quantity. Not sure how this can be done with valves / crts. Is there an equivalent resistance which could be used as a reference?

 
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Re: Leader LC910A CRT tester..

Post by marc » Fri Feb 06, 2015 1:38 pm

Hi Chris,

Marion mentioned......

"However, on this LCT910A, it tests being at the top end of the scale - well into the red zone (about level with the "90" mark on the G1 scale)."

During a conversation on PM last night Marion mentioned the Leader problem to me and from that I think she means "green zone" 90% of full deflection.
The CRT she tested is really poor according to my B&K (it hardly starts to get into the red on emission). By comparison I had a CRT here that read slightly higher into the red yet it was almost impossible to see a picture on it as to be expected by the B&K results.
The apparent huge difference between Marion's Leader and my B&K would suggest either a set up issue or fault with the Leader....As Marion has the set up guide I would lean to "fault" :aaq

Marc.

 
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Re: Leader LC910A CRT tester..

Post by crustytv » Fri Feb 06, 2015 1:56 pm

Ah OK that now makes sense.

In which case then, I would suspect and investigate any components in the Leaders cut-off (g2) circuit. Having played around with these testers and their settings observing results, when the cut-off is incorrectly set the emission reads much higher than it should.

 
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Re: Leader LC910A CRT tester..

Post by Cathovisor » Fri Feb 06, 2015 2:58 pm

The Radar range of CRT testers had 250uA movements and IIRC current was limited to that figure. The 202 seems to apply a grid bias of about 30 volts and 350 to the anode (unless this is a fault). By contrast the older one applies about 150 volts between cathode and all other electrodes when testing emission.

 
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Re: Leader LC910A CRT tester..

Post by Katie Bush » Fri Feb 06, 2015 9:32 pm

marc wrote:Hi Chris,

Marion mentioned......

"However, on this LCT910A, it tests being at the top end of the scale - well into the red zone (about level with the "90" mark on the G1 scale)."

During a conversation on PM last night Marion mentioned the Leader problem to me and from that I think she means "green zone" 90% of full deflection.

The CRT she tested is really poor according to my B&K (it hardly starts to get into the red on emission). By comparison I had a CRT here that read slightly higher into the red yet it was almost impossible to see a picture on it as to be expected by the B&K results.
Marc.


Hi Marc and Chris,

That's absolutely right.. I made a typographical boo-boo lastnight, stating a reading that was well into the red sector.. As Marc has surmised, I did actually mean well into the green sector, at 90% of FSD +/- half a division.. My mistake, sorry. :ccb :ccg

It is indeed this huge discrepancy that makes me question the LCT-910A's accuracy - Essentially, a difference of around 80% (from somewhere under 10%, to almost dead on 90%).

Tonight, I'll check the heater volts, using my Fluke 117 (True RMS) DMM, and see if I find a meaningful 45V at G1, just to verify it also to be correct, using the same DMM (failing that, my AVO 8).

If I can get at any other CRTs without having to dig for them, I'll attempt to test a few other 'known' ones to see if the same discrepancy exist with them.. If it does, I'll follow Chris' suggestion to inspect the components in the cut off circuit.

Marion

 
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Re: Leader LC910A CRT tester..

Post by Katie Bush » Sun Feb 08, 2015 10:43 pm

Hi all,

Well now, I've just had an interesting (albeit rather painful) hour or so.. Having pulled together four Mullard AW 43-80 CRTs and tested them all in turn, I have some results.

CRT No.1 (New to my collection - Unrestored TV - Not had first light - Not previously tested by me)
HTR = 6.3V
HK leakage = Nil
G1 leakage = Nil
G1 voltage = 45V (Required several readjustments during test)
Set Cut Off = Centred on marked division.. (Difficult to set and required several readjustments during test)
Read Emission = Finished at 96% of FSD.. (Emission reading began at around 20% and rose steadily over several minutes.)

HTR volts remained steady, G1 volts needed several readjustment during test, and Set Cut Off required several readjustments during test, before settling at the reading given above.

CRT No.2 (New to my collection - Unrestored TV - Not had first light - Not previously tested by me)
HTR = 6.3V (No visible light)
HK leakage = Nil
G1 leakage = Nil
G1 voltage = 45V
Set Cut Off = N/A (CRT heater is O/C)
Test = Unfinished

CRT No.3 (Spare CRT, Has been tested previously (tested good) on Marc's B&K)
HTR = 6.3V
HK leakage = Nil
G1 leakage = Nil
G1 voltage = 45V
Set Cut Off = Centred on marked division.. (Easily set, and remained steady)
Read Emission = ??105%?? (Exceeded FSD)

CRT No.4 (Tested at start of this thread - New to my collection - Unrestored TV - Not had first light - Retested for confirmation)
HTR = 6.3V
HK leakage = Nil
G1 leakage = Very low, and well within CRT tester's permitted tolerance)
G1 voltage = 45V
Set Cut Off = Centred on marked division.. (Easily set, and remained steady)
Read Emission = 91% of FSD.. This CRT was previously tested and Failed (Emission less than 10% of FSD) on Marc's B&K.

Interpret as you will...... :aaq :aab

Marion

 
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Re: Leader LC910A CRT tester..

Post by Katie Bush » Tue Jun 23, 2015 11:38 pm

Hi all,

Just a quick update, and quite an interesting turn of events!

On Sunday, I had a very welcome visit from Marc & Glenys, and after a pot of tea, sandwiches and cakes, we had a look at the Leader in a comparison test against Marc's B&K.

The strange part was, at the beginning, the Leader was showing immensely optimistic figures with regard to emission.. The figures were all consistently high, and almost all were showing near identical readings (90% or better).

Now, after trying Marc's B&K on the same CRTs, and we obtained a fair range of emission readings that gave me very strong reason to believe that there was indeed a problem with the Leader.

As it happened, we 'played' with the testers on about half a dozen different tubes, over a period of about two hours.. By the end of that time, it was becoming apparent that the Leader was beginning to come in line with the figures from Marc's B&K.. There was still a difference in the readings, but by now only marginal, let's say 'maybe' about 10% difference.. More importantly, the Leader was now showing different readings on different tubes, unlike at the start of the session when the readings were all 90% or above, even on those tubes that were known to be flat.

We discovered an unusual anomaly whilst testing one CRT, in as much as just touching the Leader's cable at the adapter plug would cause the reading to fluctuate wildly from zero to well into the green sector.. At first, it looked like we had found 'the' fault, however, repeating the same experiment on any of the other tubes had no effect, and the readings remained rock steady - our conclusion was that the tube base most likely had an issue (broken internal wire, or poor soldered joint).

In any event, by the time we had been around the block about three times, and the Leader had been powered up for most of that two hour session, we were getting quite believable readings on the Leader, and those readings were no more than 10% adrift of Marc's B&K.. The B&K giving the lower readings, which still left the Leader giving the more optimistic readings, but nothing near the kind of reading we were seeing at the start.

So, is it possible/likely that the discrepancy could have been down to something as simple as caps within the Leader just needing time to reform?

Anyway, it seems to be working properly now.... :aad :)

Marion

 
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Re: Leader LC910A CRT tester..

Post by marc » Wed Jun 24, 2015 12:52 pm

Hi Marion,

It certainly was an interesting day :aaq and thankfully your Leader now seems to be playing ball :aad
I think that right from the beginning a cap issue had been playing on my mind and after Sunday's escapade with both testers (my B&K) that seems to be proved not forgetting of course that your Leader was in immaculate condition and looked like it had never been used more than a time or two in it's entire life it's perhaps not surprising that the caps needed a touch of re-forming.

I know that one or two members find that the B&K tends to lean on the low side of true emission with monochrome CRT's but I've got used to mine and find the readings fairly near the mark with all the tests it's done and the Leader appears to give just fractionally higher readings so is probably spot on.

Just a thought Marion, maybe it was the very nice "bun munch" that inspired the Leader to work. :bba

Marc.

 
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Re: Leader LC910A CRT tester..

Post by Katie Bush » Wed Jun 24, 2015 7:19 pm

marc wrote:Hi Marion,

Just a thought Marion, maybe it was the very nice "bun munch" that inspired the Leader to work. :bba

Marc.


Hi Marc,

I wonder if we should have tried it on a 'PIE'? :aak

Marion


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