DIY Curve Tracer - Page 8 - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 15th February 2012, 02:16 AM   #71
diyAudio Member
 
SpreadSpectrum's Avatar
 
Join Date: Nov 2007
One potential problem I can see is that grids tend to draw a lot of current at low plate voltages, control grid if you are doing positive curves, screen grid no matter what. If you go slowly this could be very hard on the grids.

With a fast sweep you can draw the curves out past the tubes max dissipation and just give the tube rest periods to keep the average down. As you slow down the sweep, you may be limited in that regard.
  Reply With Quote
Old 15th February 2012, 02:43 AM   #72
TheGimp is offline TheGimp  United States
diyAudio Member
 
TheGimp's Avatar
 
Join Date: Aug 2009
Location: Johnson City, TN
I view the microprocessor option as a tool to sweep the traces rapidly so you minimize power dissipation. Most tubes have frequency response above a MHz so there is no reason (that I see) not to sweep as fast as you can within the limitations of your sweep circuit.

I've got dozens of 89C51s so Ive used them in the past, but have an Arduino Uno on order to play with.

Also, with a microprocessor you can perform the sweeps in a non-sequential order. Lowest dissipation, then highest dissipation, next lowest dissipation, next highest dissipation.....

This minimizes the peaks and pushes dissipation towards average.

Last edited by TheGimp; 15th February 2012 at 02:45 AM.
  Reply With Quote
Old 15th February 2012, 02:57 AM   #73
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
Quote:
Originally Posted by ChrisA View Post
The key is that because you are NOT driving a real time display like the analog scope, you can go as slow as you like. With the uP you do not need to retrace a curve at 60Hz, 1Hz is fine.
Working slower allows you the benefit of adjusting settling time, averaging measurements before you dump them to the host, removing outliers, and loop compensation is easier.
  Reply With Quote
Old 15th February 2012, 03:20 AM   #74
TheGimp is offline TheGimp  United States
diyAudio Member
 
TheGimp's Avatar
 
Join Date: Aug 2009
Location: Johnson City, TN
Work Slow, Sweep fast.
  Reply With Quote
Old 15th February 2012, 03:37 AM   #75
diyAudio Member
 
Michael Koster's Avatar
 
Join Date: Jan 2008
Location: Eureka, CA
Quote:
Originally Posted by SpreadSpectrum View Post
One potential problem I can see is that grids tend to draw a lot of current at low plate voltages, control grid if you are doing positive curves, screen grid no matter what. If you go slowly this could be very hard on the grids.

With a fast sweep you can draw the curves out past the tubes max dissipation and just give the tube rest periods to keep the average down. As you slow down the sweep, you may be limited in that regard.
I'm designing a system that uses pulse measurement techniques ;-) for each point e.g. I'm using a D/A converter that has an synchronous load function such that each measurement point is a brief pulse from a specified baseline condition. In this way, the dissipation can be limited by the duty cycle of the measurement pulses.

For example, each plate curve would consist of a sequence of higher and higher plate voltage pulses until some limiting condition is met e.g. I*V. For each measurement point, all electrode voltages will be pulsed together, held for a settling and measurement time, and then returned to the baseline voltages.

An arduino has good A/D capability so I am using an arduino plus a separate AD7808 D/A chip having the required global load/enable function and up to 8 10 bit outputs..

I find that 10 bit resolution is sufficient as long as there is range scaling for each electrode e.g. plate current measurement range selection of say 1mA, 10mA, 100mA, and 1A to cover a range of tubes and operating points.

I'm providing a separate power supply for each electrode (there are only 3 after all...) such that current can simply be measured by means of a shunt in the return path. Using pulse measurement, these supplies can be relatively small in terms of continuous power and have big storage caps to provide the short term current needed for the measurement pulse duration.

I'm working on a simple arduino "shield" for the AD7808 D/A converter and a simple programmable regulator to drive each electrode. A rudimentary tester/tracer would consist of an arduino board, the D/A shield, and 3 regulator boards for g1, g2, and plate. The regulator board will also carry the rectifier and filter so will only need 3 small toroids (or a toroid with 3 sec coils...) and 3 regulator boards for the electrode supplies. The programmable regulator circuit is opamp+MOSFET based, similar to the one posted earlier in this thread.

Range selection is through a rotary switch for each electrode. The arduino code would iterate through the set of points comprising the plate curves and output CSV lines for the plate curve data which could then be plotted using any of a number of apps e.g. ploticus or MS excel.

Also the tracer could be fitted with a realtime display consisting of a bitmapped LCD panel and another arduino to draw the curves. Uno boards are about $30 each and there are LCD display shields.

I want to do this as an open hardware and open software project.

PS also thinking of using it as a physical modeling box for use with spice

Last edited by Michael Koster; 15th February 2012 at 03:57 AM.
  Reply With Quote
Old 15th February 2012, 04:45 AM   #76
ChrisA is offline ChrisA  United States
diyAudio Member
 
Join Date: Jan 2008
Quote:
Originally Posted by TheGimp View Post
I view the microprocessor option as a tool to sweep the traces rapidly so you minimize power dissipation. Most tubes have frequency response above a MHz so there is no reason (that I see) not to sweep as fast as you can within the limitations of your sweep circuit.
Yes you are right, there is no reason to go slower then you have to. My point was that you don't need to go really fast.

Another thing a micro processor can do is consult a database of tube specs. so if you are testing a 6v6 tube the tester can know the max plat voltage and so on and not go over the limits. The old style testers had their "database" stored on a paper roll or chart. A new design tester would have the tables stored internally.



Now I have a question. I will also post this in the solid state forum but some one here may know. I need a MOSFET for the pass regulator for the variable plate supply. I will construct this tester to use a fixed voltage bench B+ power supply but I'll build a pass regulator using a power mosfet. So the question is "which mosfet?" I ant one that is very common that anyone can find, low cost. and over spec'd so it will be hard to fail even if some one tried to test a shorted tube. Figure that we want to be able to test power tubes like a KT88 Are there any 800 volt .5 amp mosfets. I had also thought about using a vacuum tube as the pass regulated but

the mosfet's gate will be controlled by the Arduino's analog output. But via an opto-coupler and with a 7 volt senior diode as a backup safety device to shunt high voltage to ground. I really don't want any of that 800 volts B+ getting into the USB cable even after multiple component failures and a resulting small fire. If people suggest some part numbers I'll order a couple of each and try them.

Sorry I did not mean to hi-jack this thread. I really do like the scope based tracer, it's way-cool.
  Reply With Quote
Old 15th February 2012, 06:02 AM   #77
gootee is offline gootee  United States
diyAudio Member
 
Join Date: Nov 2006
Location: Indiana
Blog Entries: 1
I've mentioned this at least once, before, somewhere. But I don't think that anyone else realized what it could mean.

Using a computer and software, with A/D converters measuring all voltages and currents of interest (which the computer would save), could free us from needing to use synchronized waveforms at all.

To make the point, maybe even noise, if large-enough in amplitude, could be used for both the high-current path drive and the control drive. The point is that the computer could measure and record for a short time and then sort and reassemble all of the measurements by voltages and currents in any way we wanted and still produce the same familiar-looking curves (except that it could show the steps for ANY values we wanted to see).

i.e. The time-sequencing of the stimuli would be unrelated to the ability to construct the desired plots.

I'm not suggesting using noise instead of waveforms, necessarily (unless it would be advantageous). Just making the point that digital sampling, storage, processing, and display-management would open a whole new universe of possibilities, and not just for the use of asynchronous or random test signals.

Imagine also collecting temperature data and plotting the curves versus temperature, or any other variable that can be measured and digitized. Long testing time periods could also be used, and/or multiple devices, and statistical plots could be created. The possibilities are probably endless. Matching or selection would be trivial to automate, for example.

Maybe a good "curve tracer" could consist of only a set of high-impedance probes and differential probes and current probes, with A/D converters, and "curve tracer" software on a computer.

It could, for example, be connected to a real device in a real application circuit. The circuit could be used for the real application, while being measured. Having collected data for the desired operating scenarios, the "curve tracer" software could assemble and present the data in whatever sets of curves one wanted to see. Or it could provide real-time plot displays like an old-fashioned curve tracer, too.

Of course, you could still also use it with a dedicated "test fixture", when desired, which would look like most of the rest of a standard curve tracer, although it might be even nicer if the test signals and settings and other functions could also be controlled by the software.

Also, imagine the possibilities for the automatic generation of Spice models.

Sorry to blather on, again. I'm sure it's all been done at places like Agilent. But even for a "typical" analog curve tracer, like what is being discussed, it would be quite simple to ADD ON the digital sampling capability (while not losing or changing any of the original capabilities), to be able to record any one of the voltages and any one of the currents of interest (or all of them at once), as numbers in a file on a standard PC. After that part was done, there would be infinite options, starting with just using off-the-shelf software to make the usual plots (even just using MS Excel, or freeware).

To do it really cheaply and easily, maybe something like a soundcard could be used as the input. Then it could be done without even knowing anything about A/D converters. (But I'm not sure if they can have their AC coupling capacitors removed to enable DC coupling or not. Might have to buy a cheap A/D board or a USB A/D box instead, or (gasp!) use a parallel or serial port.)

EDIT: Ah, cool, I see that ChrisA and others DO "get it". An Arduino or other dedicated hardware would probably be the best way to go (maybe by far; I haven't done any of the math). But I was thinking more about the fact that almost everybody already has a PC, and maybe also some old PCs that they don't even use anymore, and thought maybe there would be some basically-already-available way to get the data into the PC, at least for the case of only two data streams at a time. But wow that WOULD be very limiting, now that I think about it. I went into a Radio Shack for the first time in quite a while, last week, and they seem to have reversed course, again, at least by a bit! They actually have Arduino and Basic Stamp kits, and lots of protoboards, and some other stuff I haven't seen there for a long time! The manager said something about a new CEO or something, taking them back more toward their roots...

Cheers,

Tom

Last edited by gootee; 15th February 2012 at 06:29 AM.
  Reply With Quote
Old 15th February 2012, 12:57 PM   #78
TheGimp is offline TheGimp  United States
diyAudio Member
 
TheGimp's Avatar
 
Join Date: Aug 2009
Location: Johnson City, TN
I hope the Arduino is going to open a whole new world up to kids with scientific/engineering interests.

Since ICs took over from discrete logic there has been a continuing recession of available 'toys' so to speak, for kids to play with.

I hope this will lead to a new field of educational tools to stimulate their interest in the world of electronics.

Back to the topic of interest, I find the Arduino solves a number of issues, such as getting data into the computer (via USB), Readily available HW, Unified F/W development package, it is quite inexpensive, etc.

ChariA, I have been using the IXHF9N80 which is rated at 800V, 9A continuous, 180W, 36A peak pulse.

Even with this I have been blowing up devices in a pass regulator.

The issue is you need a lot of capacitance following the regulator to meet the peak current demand (unless you want to make it quite complex and achieve low z0 with a lot of capacitance prior to the regulator). That high capacitance means you now have to add current limit on the output of the regulator to protect it from power on surges. I finally got it stable in the curve tracer I built with the Lampizator module.

If you want some samples of the 9N80, PM me your address and I'll get them in the mail.
  Reply With Quote
Old 15th February 2012, 02:20 PM   #79
diyAudio Member
 
Michael Koster's Avatar
 
Join Date: Jan 2008
Location: Eureka, CA
I do think arduino is the way to go. I have been building and programming arduino projects for a few months now and it's hands down the easiest to work with ever. BTW, I've used a lot of different uControllers in the past and even designed bit slice processors back in the old silicon age.

Arduino doesn't have analog outputs, only PWM, so an external D/A seems like a good idea.

For Spice, I think the way to go is physical modeling, where Spice provides the inputs to drive the tester, the HW tester measures the tube currents etc., and provides the outputs back to spice. Otherwise there is still a crapload of curve fitting and trend extraction to do.

A micro-programmable tube tracer/tester would be able to do so much more than anything out there now. Imagine being able to plot the exact load line for your tube at your op point. Matching at your op point. actually measuring grid currents for A2 and screen drive designs. Fiddling with g3 voltage... It would be super easy to create a custom measurement regime for your own needs.

Using arduino, open hardware, and open source would allow many people to contribute in their own area of expertise.

As for the pass regulator, I would only ever put the storage "behind" the regulator. Also make sure that DUT and fixture capacitance doesn't cause reverse voltage to be exceeded when rapidly reducing output voltage. Gate protection diodes are essential.
  Reply With Quote
Old 15th February 2012, 03:21 PM   #80
ChrisA is offline ChrisA  United States
diyAudio Member
 
Join Date: Jan 2008
Quote:
Originally Posted by gootee View Post
I've mentioned this at least once, before, somewhere. But I don't think that anyone else realized what it could mean.

Using a computer and software, with A/D converters measuring all voltages and currents of interest (which the computer would save), could free us from needing to use synchronized waveforms at all.

To make the point, maybe even noise, if large-enough in amplitude, could be used for both the high-current path drive and the control drive. The point is that the computer could measure and record for a short time and then sort and reassemble all of the measurements by voltages and currents in any way we wanted and still produce the same familiar-looking curves (except that it could show the steps for ANY values we wanted to see).

i.e. The time-sequencing of the stimuli would be unrelated to the ability to construct the desired plots.

I'm not suggesting using noise instead of waveforms, necessarily (unless it would be advantageous). Just making the point that digital sampling, storage, processing, and display-management would open a whole new universe of possibilities, and not just for the use of asynchronous or random test signals.

Imagine also collecting temperature data and plotting the curves versus temperature, or any other variable that can be measured and digitized. Long testing time periods could also be used, and/or multiple devices, and statistical plots could be created. The possibilities are probably endless. Matching or selection would be trivial to automate, for example.

Maybe a good "curve tracer" could consist of only a set of high-impedance probes and differential probes and current probes, with A/D converters, and "curve tracer" software on a computer.

It could, for example, be connected to a real device in a real application circuit. The circuit could be used for the real application, while being measured. Having collected data for the desired operating scenarios, the "curve tracer" software could assemble and present the data in whatever sets of curves one wanted to see. Or it could provide real-time plot displays like an old-fashioned curve tracer, too.

Of course, you could still also use it with a dedicated "test fixture", when desired, which would look like most of the rest of a standard curve tracer, although it might be even nicer if the test signals and settings and other functions could also be controlled by the software.

Also, imagine the possibilities for the automatic generation of Spice models.

Sorry to blather on, again. I'm sure it's all been done at places like Agilent. But even for a "typical" analog curve tracer, like what is being discussed, it would be quite simple to ADD ON the digital sampling capability (while not losing or changing any of the original capabilities), to be able to record any one of the voltages and any one of the currents of interest (or all of them at once), as numbers in a file on a standard PC. After that part was done, there would be infinite options, starting with just using off-the-shelf software to make the usual plots (even just using MS Excel, or freeware).

To do it really cheaply and easily, maybe something like a soundcard could be used as the input. Then it could be done without even knowing anything about A/D converters. (But I'm not sure if they can have their AC coupling capacitors removed to enable DC coupling or not. Might have to buy a cheap A/D board or a USB A/D box instead, or (gasp!) use a parallel or serial port.)

EDIT: Ah, cool, I see that ChrisA and others DO "get it". An Arduino or other dedicated hardware would probably be the best way to go (maybe by far; I haven't done any of the math). But I was thinking more about the fact that almost everybody already has a PC, and maybe also some old PCs that they don't even use anymore, and thought maybe there would be some basically-already-available way to get the data into the PC, at least for the case of only two data streams at a time. But wow that WOULD be very limiting, now that I think about it. I went into a Radio Shack for the first time in quite a while, last week, and they seem to have reversed course, again, at least by a bit! They actually have Arduino and Basic Stamp kits, and lots of protoboards, and some other stuff I haven't seen there for a long time! The manager said something about a new CEO or something, taking them back more toward their roots...

Cheers,

Tom
I thought of the sound card. But I think many of them are AC coupled and can't hold a DC level (maybe) but the real problem is that I want at a minimum 6 analog inputs. I want to measure the voltage and current on every pin. Think of a pentode.

And then there is the problem than a few people will not want to risk pugging something that runs on 500 volts into a computer.

The big task for a tester like this will be software. So it is best to use something that is VERY day to program so more people can contribute. Also you wan to be multi-platform. Arudino is easy and it's development system runs on Windows, Mac and Linux equally well. As a test I wrote something that would read the voltage from a pot (wired as a voltage divider) and use PWM to have a LED brightness follow the pot while also displaying the pot's voltage on an LCD. It took all of about 20 minutes and that was the first evening I have the Arduino. So it is a very quick learning curve. OK I do software at work 25+ years at it not on Arduinos or AVRs
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
DIY Curve Tracer for PC locky_z Solid State 446 29th April 2014 01:04 AM
B-H Curve Tracer gpapag Equipment & Tools 9 16th January 2011 08:22 PM
curve tracer barclaycon Equipment & Tools 6 11th February 2010 08:10 PM
Wanted Diy curve tracer! amc32 Car Audio 1 19th October 2009 05:52 AM
DIY tube testing Curve Tracer whitelabrat Tubes / Valves 5 24th October 2007 09:11 PM


New To Site? Need Help?

All times are GMT. The time now is 06:40 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2