Re: Re: [neonixie-l] MPSA42 or MJE340?

[Dekatron42]

You can also turn the uTracer into a transistor curve tracer: 
https://www.dos4ever.com/uTracerNotebook/Notebook.html#tortester1 , I 
haven't done it but thought about it a few times.

There's also the new uTracer V6, not a kit yet but it has a weblog: 
https://www.dos4ever.com/uTracerlog6/tubetester6.html

/Martin

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Re: Re: [neonixie-l] MPSA42 or MJE340?

[Mark Moulding]

I had a 575 - two, actually; it's quite a chunk of gear, weighing in at 70 
pounds, with 39 vacuum tubes plus the CRT.  I picked them up at an auction, 
fiddled with them a bit, and decided I had other better uses for the space.

But a transistor curve tracer would still be a handy thing, and on eBay I 
stumbled across the Heathkit IT-1121, which has most of the functionality 
of the Tektronix unit without the oscilloscope (and a *lot* smaller).  To 
use it, you connect it to your own oscilloscope, which really needs to be 
an analog 'scope in X-Y mode; digital 'scopes won't work very well.  It 
does the multiple simultaneous curves and everything, just like the 
Tektronix.  It takes a little time to calibrate the oscilloscope each time, 
so I have an old HP unit that I just leave set up for the curve tracer.

There's currently one on eBay listed for parts only, which would probably 
actually be OK once the knobs were tightened back up. The circuitry inside 
is really quite simple, and there's not much that can go wrong with it.  
Heathkit also had a model IT-3121 that I think is basically the same unit.  
I also see listed a Leader LTC-905 which looks to be a very similar type of 
instrument.

If you want to trace vacuum tube curves, head over to 
https://www.dos4ever.com/uTracer3/uTracer3_pag2.html  The very nice 
gentleman there makes an entirely solid-state vacuum tube curve tracer as a 
kit, controlled by a pre-programmed PIC.  Rather than doing all the steps 
and curves simultaneously, it steps through the process, so it just needs a 
little switching supply rather than a big complex system.  It's very 
flexible, and the associated PC software (required, but free to download) 
really makes it easy.  No affiliation, just a satisfied customer.
~~
Mark Moulding


On Friday, April 24, 2020 at 3:07:57 PM UTC-7, gregebert wrote:
>
> When I was in high school, I got to use a Tek 575 curve tracer. Perfect 
> instrument to nail-down any differences between these devices.
> Every now and then, I take a look on Ebay and ask myself if I should buy 
> one. Yikes...I just took a peek and there are several available. 
> Fortunately I just bought 2 more tubes from Dalibor so I've zapped my 
> budget for now.
>
> Anyways, if someone has a curve tracer it would be really interesting to 
> compare these.
>

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Re: [neonixie-l] MPSA42 or MJE340?

['jf...@my-deja.com' via neonixie-l]

It should be easy to convert the 575 back into a tube curve tracer since it 
was a modified 570 with the filament transformer removed and the sockets 
changed.  If you can find a meterless Hickok tube tester, you have the 
sockets, switches and filament transformer you would need to convert it 
back for a single tube.  It can obviously be done by brute force, but I 
have not figured out a clever way to set it up to do A-B comparisons so you 
can find matched pairs.  Some other things you might have to add are power 
supplies for the screen and suppressor and the other elements you might 
find in a pentagrid converter (or you could derive these from the voltages 
applied to the other elements).

On Friday, April 24, 2020 at 10:00:29 PM UTC-7, Ira wrote:
>
> I have a couple of 575 that I might sell, either as is, or reconditioned 
> and calibrated (not inexpensive), with an operators manual. I also have the 
> 575 mod 122C which sports a 400V collector sweep power supply. The audio 
> people are crazy over them because they can be converted for TUBE curve 
> tracing. If interested contact me OFF of this page.   Ira. 
>
>

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Re: [neonixie-l] MPSA42 or MJE340?

[gregebert]

As much as I would love to have my own curve-tracer, I have to be 
practical. The transistors I select have SPICE models, so I simulate 
everything in detail.

Nixie tubes, especially the rare or expensive ones like b7071 and R|Z568 , 
I generate I-V curves by hand for each segment/cathode. A curve-tracer 
would help if it could export data to Excel. If I see failure or 
degradation later on, I retake the I-V data and compare it to the original 
measurements.

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Re: [neonixie-l] MPSA42 or MJE340?

[Instrument Resources of America]

I have a couple of 575 that I might sell, either as is, or reconditioned 
and calibrated (not inexpensive), with an operators manual. I also have 
the 575 mod 122C which sports a 400V collector sweep power supply. The 
audio people are crazy over them because they can be converted for TUBE 
curve tracing. If interested contact me OFF of this page.   Ira.



On 4/24/2020 8:41 PM, 'jf...@my-deja.com' via neonixie-l wrote:
You might have to settle for one of the more modern transistorized 
curve tracers.  In the last century when 500-series scopes were going 
for $20-$50, I remember talking to someone at one of the ham swaps.  
He said that they were being bought up and cannibalized by the 
audiophools because they were full of 12AX7s and other coveted tunes.


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<>

Re: Re: [neonixie-l] MPSA42 or MJE340?

['jf...@my-deja.com' via neonixie-l]

You might have to settle for one of the more modern transistorized curve 
tracers.  In the last century when 500-series scopes were going for 
$20-$50, I remember talking to someone at one of the ham swaps.  He said 
that they were being bought up and cannibalized by the audiophools because 
they were full of 12AX7s and other coveted tunes.

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Re: Re: [neonixie-l] MPSA42 or MJE340?

[gregebert]

When I was in high school, I got to use a Tek 575 curve tracer. Perfect 
instrument to nail-down any differences between these devices.
Every now and then, I take a look on Ebay and ask myself if I should buy 
one. Yikes...I just took a peek and there are several available. 
Fortunately I just bought 2 more tubes from Dalibor so I've zapped my 
budget for now.

Anyways, if someone has a curve tracer it would be really interesting to 
compare these.

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Re: Re: [neonixie-l] MPSA42 or MJE340?

['jf...@my-deja.com' via neonixie-l]

Sure, but based on the similarities in the Central Semi data sheets, the 
same die appears to be used interchangeably.  So the factors I can imagine 
is that they select and direct the leakier parts to the TO-220 package, or 
that the TO-220 package makes a difference (like allowing a higher junction 
temperature before the chip will self-destruct, or an intrinsically leakier 
package), or that the MJE is allowed to be exposed to more adverse circuit 
conditions (and they would have the same leakage in the same circuit).  
Otherwise, I lack the imagination to conjure up other plausible differences 
as long as they use the same chip.  Or maybe other manufacturers do not use 
the same chip for both part numbers, and Central decided that using their 
MPS-A42 chip would not violate the Icbo promises for the MJE-340 (from 
Motorola since Central is a second source).  If I had parts from several 
companies, I would be even more motivated to open them up and compare.

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Re: Re: [neonixie-l] MPSA42 or MJE340?

[gregebert]

It's the leakage (Icbo) that is 1000x greater in the MJE device, not the 
current gain. There are many factors affecting leakage and current gain:

   - Some are environmental (temperature, reverse-voltage, operating 
   current)
   - Some are device construction (physical dimensions of base width & 
   area; emitter area), processing (diffusion, epitaxial growth)
   - Some are chemical (doping levels for N & P)
   - Some are device physics(leakage current density, density of states, 
   etc. Lots of math here..)

The leakage is also directly proportional to the DC current gain.

The nice thing about nixie tubes is they use relatively low current, so 
most devices used for drivers wont get pushed into unsafe areas of 
operation.

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Re: Re: [neonixie-l] MPSA42 or MJE340?

['jf...@my-deja.com' via neonixie-l]

Is there a 1000X difference in the gain?  Across all lots and all operating 
conditions, I would have expected less than 10X.

On Thursday, April 23, 2020 at 3:56:44 PM UTC-7, gregebert wrote:
>
> Much of the additional leakage current is caused by the higher DC gain of 
> the MJE device; the datasheet says gain peaks around 240.
>
> Basically, the reverse-leakage current from the collector-base junction 
> gets amplified by the DC gain (beta), to produce the overall leakage (Icbo)
>

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Re: Re: [neonixie-l] MPSA42 or MJE340?

[gregebert]

Much of the additional leakage current is caused by the higher DC gain of 
the MJE device; the datasheet says gain peaks around 240.

Basically, the reverse-leakage current from the collector-base junction 
gets amplified by the DC gain (beta), to produce the overall leakage (Icbo)

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Re: Re: [neonixie-l] MPSA42 or MJE340?

[Dekatron42]

The data differs though I just read that, missed it at the first 
look.

/Martin

On Friday, 24 April 2020 00:32:28 UTC+2, Dekatron42 wrote:
>
> Central Semiconductor Corp list them as having the same die size, check 
> their documents named "Device datasheet" here 
> https://my.centralsemi.com/product/partpage2.php?part=CP310-MPSA42 and 
> here https://my.centralsemi.com/product/partpage2.php?part=CP310-MJE340, 
> now I don't know if other manufacturers have the same data on theirs, but 
> at least one manufacturer seems to use the same die in both types (maybe 
> they will confirm if you ask them?).
>
> /Martin
>
> On Friday, 24 April 2020 00:10:36 UTC+2, gregebert wrote:
>>
>> I'm absolutely certain the MJE die is physically larger. For one thing, 
>> it must conduct more thermal energy to the case.
>>
>> Another tip-off is the difference in DC current-gain, and that in-turn 
>> accounts for part of the 1000x difference in leakage current.
>> I believe leakage current is directly proportional to the area of the 
>> base (my device physics textbook is at work, and I'm at home recalling a 
>> class I took in 1983...); the actual leakage-current density is an 
>> exponential equation based on all sorts of properties of the silicon.
>>
>

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Re: Re: [neonixie-l] MPSA42 or MJE340?

['jf...@my-deja.com' via neonixie-l]

On Thursday, April 23, 2020 at 3:10:36 PM UTC-7, gregebert wrote:
> I'm absolutely certain the MJE die is physically larger. For one thing, 
it must conduct more thermal energy to the case.

I am inclined to agree, but if it were me, I would be willing to invest 
$1.08 and a half hour in the experiment.


> Another tip-off is the difference in DC current-gain, and that in-turn 
accounts for part of the 1000x difference in leakage 
> current.  I believe leakage current is directly proportional to the area 
of the base (my device physics textbook is at work,
> and I'm at home recalling a class I took in 1983...); the actual 
leakage-current density is an exponential equation based
> on all sorts of properties of the silicon.

All other things being equal, I would expect leakage to be roughly 
proportional to the chip are, which would not account for the 1000X.  Also, 
some specs in the data sheet are very loose, like guaranteed maximum 
leakage.  If the base and emitter are both diffused, I would expect these 
variations to swamp out the area.  How do they get the HV capability?  If 
it is an epi base layer, there would be variations due to the quality of 
the epitaxy that could affect the leakage.  That is a long way of saying 
that you might be right, but I don't know.


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Re: Re: [neonixie-l] MPSA42 or MJE340?

[Dekatron42]

Central Semiconductor Corp list them as having the same die size, check 
their documents named "Device datasheet" here 
https://my.centralsemi.com/product/partpage2.php?part=CP310-MPSA42 and here 
https://my.centralsemi.com/product/partpage2.php?part=CP310-MJE340, now I 
don't know if other manufacturers have the same data on theirs, but at 
least one manufacturer seems to use the same die in both types (maybe they 
will confirm if you ask them?).

/Martin

On Friday, 24 April 2020 00:10:36 UTC+2, gregebert wrote:
>
> I'm absolutely certain the MJE die is physically larger. For one thing, it 
> must conduct more thermal energy to the case.
>
> Another tip-off is the difference in DC current-gain, and that in-turn 
> accounts for part of the 1000x difference in leakage current.
> I believe leakage current is directly proportional to the area of the base 
> (my device physics textbook is at work, and I'm at home recalling a class I 
> took in 1983...); the actual leakage-current density is an exponential 
> equation based on all sorts of properties of the silicon.
>

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Re: Re: [neonixie-l] MPSA42 or MJE340?

[gregebert]

I'm absolutely certain the MJE die is physically larger. For one thing, it 
must conduct more thermal energy to the case.

Another tip-off is the difference in DC current-gain, and that in-turn 
accounts for part of the 1000x difference in leakage current.
I believe leakage current is directly proportional to the area of the base 
(my device physics textbook is at work, and I'm at home recalling a class I 
took in 1983...); the actual leakage-current density is an exponential 
equation based on all sorts of properties of the silicon.

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Re: Re: [neonixie-l] MPSA42 or MJE340?

['jf...@my-deja.com' via neonixie-l]

 

So this is a matter of academic curiosity and not an effort to make your 
device work.  I think this is a neat thing to do.  Based on your 
observations, this suggests some experiments.

 

In a previous post, I speculated that both part numbers might use the same 
chip.  I now think this is less likely.  Since this would be a destructive 
test, this should be done after all the other experiments.  You can expose 
the silicon chip by using wire cutters to scrape away the epoxy.  The chips 
will usually be bonded to the collector lead.

 

If they do use the same chip, the difference could be due to a higher 
temperature in the smaller package.  I would try using some canned Freon to 
chill the MPS-A42 to see if this changed its performance.

 

Another less likely possibility is that this is the natural variation in 
the chip processing.  You test this by comparing several parts with 
different date codes.

I am sure that creative minds can conjure up other hypotheses.

On Wednesday, April 22, 2020 at 8:03:34 PM UTC-7, Paul Andrews wrote:
>
> 
>
> Or me? Well, the MJE340 is in a larger package, but other than that, 
> nothing. 
>
>  
>

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Re: Re: [neonixie-l] MPSA42 or MJE340?

[gregebert]

There are thermal considerations; the MJE340 is designed to be used on a 
heat sink and is rated for 20W, vs 1.5W for the MPSA42.
Also, there are some differences in the safe operating area curves; the 
MJE340 can tolerate a bit more current at any given voltage.
MJE device also has a lower Vce (sat) for a given collector current.

That robustness doesn't come for free; the MJE device has 1000x higher 
leakage current.

So, as with any design, you have to look at all of the datasheet parameters 
carefully.

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RE: Re: [neonixie-l] MPSA42 or MJE340?

[Paul Andrews]

Or me? Well, the MJE340 is in a larger package, but other than that, nothing. 
What Terry said, though, is that the IN-9 requires a MJE340, not a MPSA42 
because you need to sink more current. As far as I can tell, 10mA is well 
within the current handling capabilities of both transistors, so it is 
interesting that all the designs for the IN-9 use the MJE340, whereas all the 
designs for regular nixies use the MPSA42.

I happen to have an IN-9 spectrum analyzer sitting on a breadboard that uses 
the MJE340. I swapped them out for MPSA42 and the results definitely aren’t as 
good. To stick the glow to the bottom I periodically pull the base to ground - 
so turning the tubes off. With the MJE340 this works fine. With the MPSA42, not 
so much. So either they aren’t turning off fully, or they aren’t responding 
fast enough. Temperature-wise, they were barely above ambient. YMMV.
 
From: Mac Doktor
Sent: Wednesday, April 22, 2020 9:16 PM
To: neonixie-l
Subject: Re: [neonixie-l] MPSA42 or MJE340?
 
 
On Apr 22, 2020, at 9:03 PM, 'jf...@my-deja.com' via neonixie-l 
 wrote:
 
What do you have against the MJE340?
 
Me? Nothing. All of the IN-9 projects that I've seen online use the MJE340. 
 
I'm a duffer and I'm here to learn. Paul wanted everyone to pile on so have at 
it! I'd be glad to hear more.
 
 
Terry Bowman, KA4HJH
"The Mac Doctor”

"Never install version point-zero of anything"
 
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Re: [neonixie-l] MPSA42 or MJE340?

[Mac Doktor]

> On Apr 22, 2020, at 9:03 PM, 'jf...@my-deja.com' via neonixie-l 
>  wrote:
> 
> What do you have against the MJE340?

Me? Nothing. All of the IN-9 projects that I've seen online use the MJE340. 

I'm a duffer and I'm here to learn. Paul wanted everyone to pile on so have at 
it! I'd be glad to hear more.


Terry Bowman, KA4HJH
"The Mac Doctor”

"Never install version point-zero of anything"

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Re: [neonixie-l] MPSA42 or MJE340?

['jf...@my-deja.com' via neonixie-l]

What do you have against the MJE340?  Is it too large?  Is it too much more 
money (onesies retail in Silicon Valley is 34 cents versus 75 cents)?  If I 
had to go out and buy new parts in hobby quantities, I would get the MJE340 
and not invest any more brain power, but if it was going to be used in 
quantities of thousands I would choose more deliberately.  If I already had 
some MPS-A42's on hand, I would wire it in to the circuit and test to see 
how hot it gets, and switch to the MJE340 if it got noticeably warm. Oor 
you could do the Spice modeling and formal thermal analysis.  Actually, it 
would not surprise me if you opened them up and found that they used the 
same chip and differed only in the massiveness of the packages.


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Re: [neonixie-l] MPSA42 or MJE340?

[Paul Andrews]

Both transistors are rated for 500mA, so I don’t see why you need a MJE340 for 
an IN-9. This is particularly relevant for me as I want to switch around 50mA 
using 3.3V. Not sure what the voltage is right now, given that this is the 
cathode.

> On Apr 22, 2020, at 5:25 PM, Mac Doktor  wrote:
> 
> On Apr 22, 2020, at 9:39 AM, 'jf...@my-deja.com' via neonixie-l 
>  wrote:
>> 
>> I would say whichever is cheaper, keeping in mind that nothing is cheaper 
>> than free from the junque box.  I used the floor sweepings  (advertised as 
>> npn 300V and 10W) from Poly Paks, and none of these have failed yet.  I did 
>> have one genuine Motorola MPSA92 fail after 40 years of service.  Just make 
>> sure you are driving your transistors into saturation.  Obviously TO92 is 
>> smaller than TO220, and this might be a factor in your application.
> 
> 
> The perfect example of this is driving an IN-13 vs an IN-9. The former will 
> work with an MPSA42 but the latter requires an MJE340 because of the higher 
> current. It's well known that the bargraph tubes work more reliably if 
> they're strobed; all of the circuit examples in Russian data sheets for the 
> IN-9 and IN-13 use a half-wave rectified 220V mains power source. And now I 
> finally understand a circuit modification I saw in a forum thread that has 
> puzzled me for some time. The OP couldn't get an IN-9 (using an MJE340 of 
> course) to work reliably using a generic barpgraph driver circuit. One of the 
> replies added a 555 running at 50Hz driving a MPSA42 in series with the 
> MJE340. What? How could you use the smaller trans... Now I get it. The MPSA42 
> was being used as a switch. DUHH.
> 
> Thank you for that insight. Cue up the next great mystery of life...
> 
> 
> Terry Bowman, KA4HJH
> "The Mac Doctor"
> 
> https://www.astarcloseup.com/
> 
> "Every kid starts out as a natural-born scientist, and then we beat it out of 
> them. A few trickle through the system with their wonder and enthusiasm for 
> science intact."—Carl Sagan, Psychology Today, 1996
> 
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Re: [neonixie-l] MPSA42 or MJE340?

[Mac Doktor]

On Apr 22, 2020, at 9:39 AM, 'jf...@my-deja.com' via neonixie-l 
 wrote:
> 
> I would say whichever is cheaper, keeping in mind that nothing is cheaper 
> than free from the junque box.  I used the floor sweepings  (advertised as 
> npn 300V and 10W) from Poly Paks, and none of these have failed yet.  I did 
> have one genuine Motorola MPSA92 fail after 40 years of service.  Just make 
> sure you are driving your transistors into saturation.  Obviously TO92 is 
> smaller than TO220, and this might be a factor in your application.


The perfect example of this is driving an IN-13 vs an IN-9. The former will 
work with an MPSA42 but the latter requires an MJE340 because of the higher 
current. It's well known that the bargraph tubes work more reliably if they're 
strobed; all of the circuit examples in Russian data sheets for the IN-9 and 
IN-13 use a half-wave rectified 220V mains power source. And now I finally 
understand a circuit modification I saw in a forum thread that has puzzled me 
for some time. The OP couldn't get an IN-9 (using an MJE340 of course) to work 
reliably using a generic barpgraph driver circuit. One of the replies added a 
555 running at 50Hz driving a MPSA42 in series with the MJE340. What? How could 
you use the smaller trans... Now I get it. The MPSA42 was being used as a 
switch. DUHH.

Thank you for that insight. Cue up the next great mystery of life...


Terry Bowman, KA4HJH
"The Mac Doctor"

https://www.astarcloseup.com/

"Every kid starts out as a natural-born scientist, and then we beat it out of 
them. A few trickle through the system with their wonder and enthusiasm for 
science intact."—Carl Sagan, Psychology Today, 1996

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