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uTracer - tube curve tracer [kit]



 
 
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  #1  
Old October 8th 16, 12:22 AM posted to rec.audio.tubes
Patrick Turner
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Default uTracer - tube curve tracer [kit]

You have chatted about tube curve tracers.......

after having a close look at the web site, it's a somewhat simple curve
tracer design, though not the way I would've designed it [example,
flyback HV stepup with linear regulator on the output for the plate
supply]. but it does look pretty straightforward and simple for someone
who just wants a curve tester and doesn't mind doing patch cables to
make it work.


I've been kicking around the idea of making one of these that had ZERO
patch cables, and could efficiently deliver up to 0.5A for the plate (at
certain voltages), and at the same time, enough current for the heater
power. Some edge conditions for KT-series power tubes can conduct some
serious current (up to 1/2 an amp), and the heaters can suck up 12W or
so. If the power tube can't deliver it's max current at the correct
plate voltage, it's essentially "going bad".

anyway, that's something that an emissions-only tester wouldn't be able
to test for.

but yeah, this particular curve tester goes up to 200ma which probably
covers most tubes.

I think the FIRST thing anyone should do to plot the Ea vs Ia average characteristics of a tube is to have a real good look at the schematics used in 1955, well before solid state and digital.
It is most remarkable that in 1955, curves were produced which gave us a fairly good guide to use for load line analysis.

Why do we not build on the skills of those who preceded us?

I see that gadget at that link to the site for a curve tracer to be something absolutely could not be repaired and serviced if one of the 2 billion devices went phut due to high volts from tube tests.
I see a toy, not a tool.

To test output tubes for class A you need to have Ea max up to 1,000V. If you have an SE 6550 with Ea = 500V, Ia = 50mA, then the anode swing is +/- 450Vpk with a load of say 9k0. The problem with much tube data curves for Ea vs Ia is that very poor undefined data is available for the operation with LOW Ia typically used.
My solution to not having a tube tester or a curve tracer or having reliable old data curves, or curves for newer Russian tubes is to set up a tube in a dummy class A SE amp and measure THD and Ra then calculate gm g1 and and gm g2 and µ g2 and µg2 to obtain the average properties at the idle condition - and its these properties we employ for listening to 90% of music.
I have done a couple of new web pages to explain all this more better, but having some trouble with page uploads and getting rid of an unwanted tracking program that self-installed.
Patrick Turner.
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  #2  
Old October 8th 16, 02:12 AM posted to rec.audio.tubes
Big Bad Bob
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Posts: 351
Default uTracer - tube curve tracer [kit]

On 10/07/16 16:22, Patrick Turner so wittily quipped:
> I think the FIRST thing anyone should do to plot the Ea vs Ia average characteristics of a tube is to have a real good look at the schematics used in 1955, well before solid state and digital.
> It is most remarkable that in 1955, curves were produced which gave us a fairly good guide to use for load line analysis.
>
> Why do we not build on the skills of those who preceded us?


in my own personal opinion, I'd like to build something automated, using
some kind of computing device. my device of choice, a microcontroller.
It's really the same BASIC idea, apply a voltage and measure the
current, but with automation.

in the case of the device mentioned online, it's using patch cables. I
would rather use electronic switching to do the same thing, but no
relays or klunky mechanical switches. And switching regulators that can
be controlled via the CPU to create the various voltages.

> I see that gadget at that link to the site for a curve tracer to be something absolutely could not be repaired and serviced if one of the 2 billion devices went phut due to high volts from tube tests.


you probably have a point, yeah. A properly designed system would be
hardened and able to be short-circuited without damage.

> I see a toy, not a tool.


it wasn't my preference for a design, but it _does_ "work"

> To test output tubes for class A you need to have Ea max up to 1,000V.


that's a very good point. And possibly higher. hardest part is getting
devices that behave well at those voltages. It's likely that a IGBT
device would do it, though, driven by opto-isolator and/or AC signal
with blocking capacitors. I've thought of both of these possibilities,
actually. Opto-isolator is probably the better solution. AC+blocking
capacitor might work well for the gate drive, though, to provide
sufficient voltage to turn the thing on [via an optoisolator again].

> If you have an SE 6550 with Ea = 500V, Ia = 50mA, then the anode swing is +/- 450Vpk with a load of say 9k0.


right, and you want to curve-trace a tube through its entire operating
range if possible [without doing damage to the tube, naturally] to
verify that it's working properly.


> My solution to not having a tube tester or a curve tracer or having reliable old data curves, or curves for newer Russian tubes is to set up a tube in a dummy class A SE amp and measure THD and Ra then calculate gm g1 and and gm g2 and µ g2 and µg2 to obtain the average properties at the idle condition - and its these properties we employ for listening to 90% of music.


interesting point, having a set of SE output transformers to test output
signals with. "dial-an-impedence" and then let 'er rip. Expensive,
though. I'm looking for low overall cost.

> I have done a couple of new web pages to explain all this more better, but having some trouble with page uploads and getting rid of an unwanted tracking program that self-installed.


TRACKING program that self-installed? that sounds kinda, bad... [like a
virus infection]

[FYI I hand-code all of my HTML, don't use any of those web page 'admin'
systems, rarely use scripting if it's not doxygen-generated
documentation... have never seen anything 'injected' at all]


  #3  
Old October 9th 16, 09:15 AM
John L Stewart John L Stewart is offline
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Location: Toronto
Posts: 301
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interesting point, having a set of SE output transformers to test output
signals with. "dial-an-impedence" and then let 'er rip. Expensive,
though. I'm looking for low overall cost.
[color=blue][i]

No need for several OPT's of various ratios.

Simply place the load Rl across the primary of one good OPT, find the load that gives the desired result. Works in SE or PP, I've often done it that way.

Cheers to all those still standing here, John L Stewart
  #4  
Old October 11th 16, 04:18 PM posted to rec.audio.tubes
Peter Wieck
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Posts: 2,418
Default uTracer - tube curve tracer [kit]

On Friday, October 7, 2016 at 9:11:45 PM UTC-4, Big Bad Bob wrote:

> interesting point, having a set of SE output transformers to test output
> signals with. "dial-an-impedence" and then let 'er rip. Expensive,
> though. I'm looking for low overall cost.


Consider your target audience. If the item is too 'inexpensive' (cheap) they will not value it.

This is an interesting concept in itself. Tube "testers" are such a strange collection of beasts, with modern solid-state devices giving all sorts of additional information over the older devices - yet all the essential tube topologies were done-and-done, essentially by 1965, if not earlier

Peter Wieck
Melrose Park, PA
  #5  
Old October 13th 16, 12:33 AM posted to rec.audio.tubes
Big Bad Bob
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Posts: 351
Default uTracer - tube curve tracer [kit]

On 10/09/16 01:15, John L Stewart so wittily quipped:
> Simply place the load Rl across the primary of one good OPT, find the
> load that gives the desired result. Works in SE or PP, I've often done
> it that way.


that works up to a point, but if you need "that much power" it becomes
harder selecting something that can perform at the extremes.

still not a bad idea. If I could get away with 8 ohms through 100 ohms
on the secondary, it'd probably work. Using a frequency close to 1khz
might help. but yeah, average OPT won't handle the 50W (let's say) from
a mega-tube running in triode config class A SE mode. So at least one
"big fat transformer" to handle THAT one, then if the interelectrode
inconsistencies don't cause something *nasty* to happen, put a 1k load
on it for small fry... ?

some low power SE triodes might want 20k impedence. Others might want
2k. so 100 ohms to turn a ~2k into a >20k impedence on the primary,
assuming that a) inductance is sufficient, and b) impedence matching
like that is relatively linear.


 




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