Good morning tube amateurs, I'm looking for curve tracer hardware design suitable for connection to external oscilloscope, in order to perform measurement on sweep tubes such as the marvelous posted in #1413 dated 2021-02-14 (page 71 of "Those Magnificent Television Tubes"). Any suggestion for schematics or second hand equipment? Something equivalent to Tektronix 570 but with external oscilloscope. Thank you
You could get an Instruction Manual for the Tektronix 576, it's like 1 inch thick, with schematics, service information, circuit descriptions, parts lists, everything. Either the real manual or on CD.
You can also get key parts like the step generator and collector (plate) supply, power supply, display amplifier .....
The step generator:
https://www.ebay.com/itm/145488175207?itmmeta=01HS4GF1F0JVQFV37VNHZ1SHGC&hash=item21dfc56067:g:VV0AAOSwzBVlc2I0&itmprp=enc:AQAIAAAA0IMzL/IlmXg2siKqwMw56Av9gY2/75GSJ4SYiROMa4J6iNwYhiGUHUc6y0qshaxO/jL9D6PaE6ff/qFMu8CnmRyWhDgivQ8VcrTghMZuFmJXk3NNM/x4OPEquNwyCQ5qfMXtJYorQca3oMd2bPTW5VE28acuQsBzxi7yAyhOIFGf3XUKCsOwXPmr6wqiI3rSHy1NcYOOzY7UPK53XO3S2DJxuo5u8BM1vgwxJdd+5ksPbGtgMGmpO2SuiYk3YcNMDLFtilbijWD9HuIekK6UhXc=|tkp:Bk9SR8yXvJDJYw
You will need the step generator selector switch to go with the PC board. Part # 670-1025-02
I don't see one currently on Ebay, but they come up from time to time.
The power supply regulator board:
https://www.ebay.com/itm/1454830737...B34E8P&hash=item21df7788a8:g:7rgAAOSwHoplb9tX
The 576 collector (plate) supply assembly:
https://www.ebay.com/itm/145442662386?itmmeta=01HS4J0120XSQC34E068A5K1AV&hash=item21dd0ee7f2:g:KIMAAOSwZ8tlV7PD&itmprp=enc:AQAJAAAA8HYltfnkiZXvTTwO6J1oB9Y/NG1IHdopVVmZu6Z/TBwqYMETnH3AzYNUncILfXNalfqhK118hVSBc35rUlNLFcbUsYfZ7eJq5fm5KUOxBOHUvXNOzaKKe6eMcJPn8bWu75UF/Xc9sQ38XBhWksxGCZQIAIvJdv2IwFD14HixrFcwSGINQj+RtvXstKz7NE5S8V1ys2bmZBSgR2KX8N96ggk+Ke9vCRlMmuzW+9Fssaxzp4cb5k5qtAdhyMSfIFozvaMUuF/+q2BHto+bX0E10q7xNSkeRRXyzmDyPwHnvinuGtK2fbhgrSuNtwvEmU/fog==|tkp:Bk9SR4qRgJLJYw
Probably cheaper to get a complete used 576 and fix it.
You can also get key parts like the step generator and collector (plate) supply, power supply, display amplifier .....
The step generator:
https://www.ebay.com/itm/145488175207?itmmeta=01HS4GF1F0JVQFV37VNHZ1SHGC&hash=item21dfc56067:g:VV0AAOSwzBVlc2I0&itmprp=enc:AQAIAAAA0IMzL/IlmXg2siKqwMw56Av9gY2/75GSJ4SYiROMa4J6iNwYhiGUHUc6y0qshaxO/jL9D6PaE6ff/qFMu8CnmRyWhDgivQ8VcrTghMZuFmJXk3NNM/x4OPEquNwyCQ5qfMXtJYorQca3oMd2bPTW5VE28acuQsBzxi7yAyhOIFGf3XUKCsOwXPmr6wqiI3rSHy1NcYOOzY7UPK53XO3S2DJxuo5u8BM1vgwxJdd+5ksPbGtgMGmpO2SuiYk3YcNMDLFtilbijWD9HuIekK6UhXc=|tkp:Bk9SR8yXvJDJYw
You will need the step generator selector switch to go with the PC board. Part # 670-1025-02
I don't see one currently on Ebay, but they come up from time to time.
The power supply regulator board:
https://www.ebay.com/itm/1454830737...B34E8P&hash=item21df7788a8:g:7rgAAOSwHoplb9tX
The 576 collector (plate) supply assembly:
https://www.ebay.com/itm/145442662386?itmmeta=01HS4J0120XSQC34E068A5K1AV&hash=item21dd0ee7f2:g:KIMAAOSwZ8tlV7PD&itmprp=enc:AQAJAAAA8HYltfnkiZXvTTwO6J1oB9Y/NG1IHdopVVmZu6Z/TBwqYMETnH3AzYNUncILfXNalfqhK118hVSBc35rUlNLFcbUsYfZ7eJq5fm5KUOxBOHUvXNOzaKKe6eMcJPn8bWu75UF/Xc9sQ38XBhWksxGCZQIAIvJdv2IwFD14HixrFcwSGINQj+RtvXstKz7NE5S8V1ys2bmZBSgR2KX8N96ggk+Ke9vCRlMmuzW+9Fssaxzp4cb5k5qtAdhyMSfIFozvaMUuF/+q2BHto+bX0E10q7xNSkeRRXyzmDyPwHnvinuGtK2fbhgrSuNtwvEmU/fog==|tkp:Bk9SR4qRgJLJYw
Probably cheaper to get a complete used 576 and fix it.
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Here is a picture taken while making mods to the Tektronix 576 to curve trace tubes. The Step Amplifier (on the big heatsink ) gets modded with higher voltage transistors to handle steps going up to +/- 170V total. Some caps and diodes around the Step Amp get up-rated for higher V too. And a boost supply for the step amplifier gets added in the bottom right corner. The Step Generator PC board is swung out at the bottom to access the Step Amplifier.
Back to components. Here is the LV xfmr that runs the unit:
https://www.ebay.com/itm/3260457374...OkCK2nBMRnITUiZIfVf6Ku8uT/Q=|tkp:BFBMptXumslj
Back to components. Here is the LV xfmr that runs the unit:
https://www.ebay.com/itm/3260457374...OkCK2nBMRnITUiZIfVf6Ku8uT/Q=|tkp:BFBMptXumslj
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Here is an interesting product for the Tek 576, a Grid Step Amplifier 10X (to -200V ) for testing tubes. You don't have to mod the 576 for tubes with this. Must be new, I hadn't seen this before. 20 mA drive capable. Only does usual - grid voltages, so won't allow + screen grid curve tracing.
You will need two of these to conveniently compare two tubes on the two test channels. Umm, maybe can use just one to drive both tubes grids simultaneously.
https://www.ebay.com/itm/266682053587?itmmeta=01HS55CGA8E6E5XT23HN0RKH49&hash=item3e177d33d3:g:S7gAAOSwHfVl0vO~&itmprp=enc:AQAIAAAAwKeEKKALASOuOfVO17pf1grFLnpjWJTKjtGpVz5fxO9KP0vx5BV4wxTLbAVL297uJEEECAdoRuXfkm6Qa/usOpeSZsQzl1gjIh1nrO0I/E+QZWJwRMul1jSUzyGKBbKfzetA2wPaI6X+mJWwvxtmX4XCVplORdTUDIjCX/b++ZmVq02vPG7e6LWgrunLuZhlPbv54cwI+gOeOkALN4HAz/olOQLqMspL30L9zPoPgVnypWMwFnJtG9dPCXm4NNiToQ==|tkp:Bk9SR6iFsqXJYw
You will need two of these to conveniently compare two tubes on the two test channels. Umm, maybe can use just one to drive both tubes grids simultaneously.
https://www.ebay.com/itm/266682053587?itmmeta=01HS55CGA8E6E5XT23HN0RKH49&hash=item3e177d33d3:g:S7gAAOSwHfVl0vO~&itmprp=enc:AQAIAAAAwKeEKKALASOuOfVO17pf1grFLnpjWJTKjtGpVz5fxO9KP0vx5BV4wxTLbAVL297uJEEECAdoRuXfkm6Qa/usOpeSZsQzl1gjIh1nrO0I/E+QZWJwRMul1jSUzyGKBbKfzetA2wPaI6X+mJWwvxtmX4XCVplORdTUDIjCX/b++ZmVq02vPG7e6LWgrunLuZhlPbv54cwI+gOeOkALN4HAz/olOQLqMspL30L9zPoPgVnypWMwFnJtG9dPCXm4NNiToQ==|tkp:Bk9SR6iFsqXJYw
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If you have a PC a uTracer (link here) does it all, although some people like to use an external heater supply.
For Sweep tubes you'll want to be able to test plate current up to at least 500 mA. Some big Sweep tubes can even do a couple of Amps peak. (6LW6, 26HU5, 6LX6, ....) You may want plate voltage range up to 600V or more.
You may also want to do positive +Vg2 sweeps too, like on the data sheets, maybe to +350V, which can take some 40 or 50 mA current from the stepper.
The Tek 576 can handle up to 200 Watt tubes. 1500 V plate V max. I actually modded that down to 750V max with a rectifier wiring mod, for safety reasons. So 400V and 750V plate sweeps are what I typically do on the 576. There is a Variac adjustment knob on the front for reducing max V ranges too.
I also modded the step generator to optionally do 15 traces instead of the usual 10 (or less) standard. ( Just had to pull one IC pin up and wire in a different resistor into the D/A circuitry. ) Step size is also continuously variable with a knob on the side. Easy to read out the actual step V.
15 trace example below:
You can also do Vgrid to Plate current scans to check linearity of tube gm.
I use some digital readout, adjustable current limit, bench supplies for heater voltages and screen grid voltages. (Vg2 switches in automatically when running curves.)
A toggle lever on the device connect box allows you to flip between two tubes quickly for comparison/matching.
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I should mention pricing etc for Tek 576 curve tracers (on Ebay).
I got the one I use for tube tracing on Ebay nearly 20 years ago as a good working unit for $600 (and $100 for shipping). Lately I see good working units for $1500 and up. However, not working units I've seen for $400 to $600 lately. I ordered a $400 one for spare parts a few years ago, and the only thing wrong with it was a relay needed replacing. I use it for SS tracing now. The clear plastic safety cover generally disappears early on, and users stick a pencil in the slot for the HV safety over-ride switch. which works poorly, with the HV xfmr relay chattering away until the contacts burn up. So $5 for a new plug-in relay. I added a toggle switch to over-ride HV safety. (needed for tubes anyway, they don't fit under the cover) The front panel Variac may have a burn spot on it if its been used for high power SS tracing. Mine had a rough spot there, so I replaced it.
The calibration may need touching up on these old antiques, but both of mine were near spot on. The great big Tek 576 Instruction Manual gives extensive Calibration procedures, schematics, parts lists, circuit descriptions and service instructions. You will want one.
Knobs tend to crack if they were over tightened. Can sometimes find used ones on Ebay. If there is no sign of a trace, the CRT HV supply xfmr may have failed. You can get used 576 HV CRT supplies on Ebay. And there are winding instructions on the Net if you want to try re-winding the old one. The later Rev 03 HV units with silicone potting are said to be very reliable. New CRTs are near impossible to find, but these rarely fail. Used ones show up on Ebay occasionally. Older 576 CRT units will typically get a small burn spot on the screen where the idle beam sits at 0,0. Not generally a big problem, just a giveaway as to how much use it has had.
The one thing that does crap out on these units commonly are the push-button switches on the front panel. Especially the "Invert" button for NPN or PNP display mode and the Step Gen polarity "Invert" button. These use Centralab multi contact switches, which I have just bought newer units for and swapped out the slider along with its contact springs. After a little grinding the plastic end to fit well, it's like new! No de-soldering. Don't clean the actual Push Button faces, the lettering is just painted on.
The rotary cam switches (right side knobs) are known for getting dust in them, they do have dust covers. You just blow the dust out. Rarely a problem. I have seen replacement contact fingers for these, but the only problem one I found was a higher current contact for a light bulb. The gold plated PC foil was what wore out, so I just bent the spring sideways a little to land on a different foil location.
I got the one I use for tube tracing on Ebay nearly 20 years ago as a good working unit for $600 (and $100 for shipping). Lately I see good working units for $1500 and up. However, not working units I've seen for $400 to $600 lately. I ordered a $400 one for spare parts a few years ago, and the only thing wrong with it was a relay needed replacing. I use it for SS tracing now. The clear plastic safety cover generally disappears early on, and users stick a pencil in the slot for the HV safety over-ride switch. which works poorly, with the HV xfmr relay chattering away until the contacts burn up. So $5 for a new plug-in relay. I added a toggle switch to over-ride HV safety. (needed for tubes anyway, they don't fit under the cover) The front panel Variac may have a burn spot on it if its been used for high power SS tracing. Mine had a rough spot there, so I replaced it.
The calibration may need touching up on these old antiques, but both of mine were near spot on. The great big Tek 576 Instruction Manual gives extensive Calibration procedures, schematics, parts lists, circuit descriptions and service instructions. You will want one.
Knobs tend to crack if they were over tightened. Can sometimes find used ones on Ebay. If there is no sign of a trace, the CRT HV supply xfmr may have failed. You can get used 576 HV CRT supplies on Ebay. And there are winding instructions on the Net if you want to try re-winding the old one. The later Rev 03 HV units with silicone potting are said to be very reliable. New CRTs are near impossible to find, but these rarely fail. Used ones show up on Ebay occasionally. Older 576 CRT units will typically get a small burn spot on the screen where the idle beam sits at 0,0. Not generally a big problem, just a giveaway as to how much use it has had.
The one thing that does crap out on these units commonly are the push-button switches on the front panel. Especially the "Invert" button for NPN or PNP display mode and the Step Gen polarity "Invert" button. These use Centralab multi contact switches, which I have just bought newer units for and swapped out the slider along with its contact springs. After a little grinding the plastic end to fit well, it's like new! No de-soldering. Don't clean the actual Push Button faces, the lettering is just painted on.
The rotary cam switches (right side knobs) are known for getting dust in them, they do have dust covers. You just blow the dust out. Rarely a problem. I have seen replacement contact fingers for these, but the only problem one I found was a higher current contact for a light bulb. The gold plated PC foil was what wore out, so I just bent the spring sideways a little to land on a different foil location.
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There are the old Tektronix 7CT1 and 5CT1 curve tracer O'scope plug-ins. They fit 7000 or 5000 series Oscilloscopes. Combined with that Grid Step Amplifier product above, they could trace tubes. But don't expect to do any power tubes with them. The Instruction Manuals might be interesting for ideas.
https://www.ebay.com/itm/255954193740?epid=1501481144&itmmeta=01HS6TEEJAFTX68YKT645FTPJ7&hash=item3b980f0d4c:g:YqAAAOSwh4Nj2EDs&itmprp=enc:AQAJAAAA0Ip1WZkgJxXA/EBil5aFQAd/Bo98jLFHqDmfURPhBnB9CEo5hJNHaBFe06Vb2MPYx8rsqg1862abMumFuwY1x3315LqExlNy95xhPQl8QHVzEk9gZ+WZ6qwSc+I8JJpUySDjSFhDu1mRuxic9gSMjyElCtxKuFy/ZpAU7kLZfVGnI3IdJe1YNx+Q1CNy5Qm+z4TjX2ZzhRzNyQ5Y03TpECqyrSEl0NIk7BObjU3P8KNk94WPSvYc8r+Qk4h4SHFKo2/Vi54C/IHwIRt51C4Rv8E=|tkp:Bk9SR6bpudrJYw
https://www.ebay.com/itm/116079427948?itmmeta=01HS6TEEJC0EBB97WSMMDKSNT2&hash=item1b06df816c:g:R8IAAOSw26Nl2jpI&itmprp=enc:AQAJAAAA8KnqGuVcccltye+W3HKo9F51932AAO1sE8KULqzsUlrL+v36AQKhhPtHiUsBZJczMobPkEI0WSIt4e5hPNvyB3wMt1OA5NxIM7f7iti7DA6VRdpKSD2CgO/VK7TCZ7xayD6Dn0p0HxvnXDY5p3MnHtjfNso/6tkIcEej5R94VN9XpA5OYsgulOvBKKLxlsg7+5zMHkRe6DstKkPIqrtByDRFJyDOnhv6nogoKGEg7UqJfNozP+phVWqvz9PeofDgwlLJvKy185h5dk5xO6dQnMA9+7CS86V0YRLYyUZXrozvdNzgvhxSMzMrj7SIavXl1A==|tkp:Bk9SR67pudrJYw
I forgot to mention the electrolytic caps, especially the big ones in the power supply. You can test the supply voltages for ripple at their test points, but generally it's time to replace these caps now. These generally dry out with age and loose capacitance and develop high internal resistance.
One unusual thing the 576 allows you to check is tube hysteresis, by changing the plate voltage sweep direction between alternate traces. Some tubes will show different "knees" depending on the direction scanned.
Also some complaints about the "pulsed" spot testing done by many PC tracers. The tube does not heat up under those conditions. Some electrode dimensions will change slightly when hot. I've seen weak tubes "melt" gm wise when they get hot.
I've heard complaints about the PC curve tracers being slow to display results. The real time curve tracers, like the 576, let you change parameters like tube bias or screen voltage and see immediate effects. The PC tracers have the advantage however of storing display files and some post processing results like tube gm or mu measurements or load lines. Having a library of tube results should make selecting matched tubes from a large quantity of tubes much easier too.
One unusual thing the 576 allows you to check is tube hysteresis, by changing the plate voltage sweep direction between alternate traces. Some tubes will show different "knees" depending on the direction scanned.
Also some complaints about the "pulsed" spot testing done by many PC tracers. The tube does not heat up under those conditions. Some electrode dimensions will change slightly when hot. I've seen weak tubes "melt" gm wise when they get hot.
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Hysteresis in tubes. Spangenberg
Something to do with unstable movement of the virtual cathode.
https://www.diyaudio.com/community/...how-at-low-current.362456/page-2#post-6400304
I can see two kinds of knees with some tubes on the curve tracer. Shows up when the tracer is timed for alternate traces done in opposite directions. 6JK6 is one.
Something to do with unstable movement of the virtual cathode.
https://www.diyaudio.com/community/...how-at-low-current.362456/page-2#post-6400304
I can see two kinds of knees with some tubes on the curve tracer. Shows up when the tracer is timed for alternate traces done in opposite directions. 6JK6 is one.
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Todays curve tracers use computers and screens for display, and they are overall easier if you ask me.
The Tube Hysteresis effect referenced above could be a VHF oscillation, as Keit suggested in the referenced thread. Rectified by the display vertical amplifier to look like hysteresis. TV sets had an effect called "snivets" where a VHF oscillation around the Horizontal sweep "knees" interfered with the video reception in the VHF. In which case it would seem to be a hysteretic VHF oscillation here. Putting +10 to +15 Volts on grid 3 or the beam former plate fixes either problem. 5/6JK6 is fixable this way.
The low plate current, low plate V kinks that Keit was concerned about (point of the thread, for pentodes/beam pent.) seem to be strongly grid2 voltage related. Not sure that this got resolved as to the tube design issue. 26LX6 (a Sweep tube) demonstrates this moderately. Some tubes have really big kinks there, 25DN6 for example. And low screen current tubes have minor kinks, 21LG6. Grid2 drive or Crazy drive magically removes the kinks. But other pentodes don't have any kinks to start with, 6197. 6197 does not have grid wire alignment. But 12HL7 does not either, but has the kinks back. I'm sure grid wire alignment is part of the story, but apparently not the whole story. Some more fun curve tracing needed. I have one sweep tube where grid2 is perfectly mis-aligned, g2 gets hot real fast.
pics: 26LX6grid1drive, 26LX6Crazydrive, 25DN6grid1drive, 25DN6grid2drive, 21LG6grid1drive, 6197grid1drive, 12HL7grid1drive
The low plate current, low plate V kinks that Keit was concerned about (point of the thread, for pentodes/beam pent.) seem to be strongly grid2 voltage related. Not sure that this got resolved as to the tube design issue. 26LX6 (a Sweep tube) demonstrates this moderately. Some tubes have really big kinks there, 25DN6 for example. And low screen current tubes have minor kinks, 21LG6. Grid2 drive or Crazy drive magically removes the kinks. But other pentodes don't have any kinks to start with, 6197. 6197 does not have grid wire alignment. But 12HL7 does not either, but has the kinks back. I'm sure grid wire alignment is part of the story, but apparently not the whole story. Some more fun curve tracing needed. I have one sweep tube where grid2 is perfectly mis-aligned, g2 gets hot real fast.
pics: 26LX6grid1drive, 26LX6Crazydrive, 25DN6grid1drive, 25DN6grid2drive, 21LG6grid1drive, 6197grid1drive, 12HL7grid1drive
Oh yeah! I forgot to mention that the Tek 576 has selectable pulse testing too, besides the continuous line testing. Selectable 80 uSec or 300 uSec pulses. You get a string of dots for the display. You get both schemes with the 576.
The 576 also has selectable external inputs for Vertical or Horizontal display (normally from the High Current plug-in). I brought them out to BNC connectors with enable switches. I've used the Vertical input to connect an AM503 DC Current Probe for visualizing tube screen current during curve testing. Probably just what is needed for figuring out those nasty tube kinks.
And, it's even all ready for P type tubes in the future.
Well it still does PNP bipolars and P channel Mosfets anyway. Some P tube emulation circuit could be tested readily.
The one upgrade I still have in mind to do is a second complementary stepper output, for testing differential tube setups. There are several ways to do this.
Easiest would be just an Inverter, or more elaborately a second synchronized step generator board and step amplifier for it, and ultimately a second synchronized 576. That has the advantage of two simultaneous displays, separate offset controls.... And it's already sitting on the bench! ( Thank you $5 relay! )
I read something in the Tek 576 manual once about some sneaky option you get by pressing two step gen push buttons at once. I think it was for just such synchronizing of two 576 units. Have to go find that again.
The other two tube extension I would like to do would be for combining two tubes in Push-Pull. Have to do plate current subtraction for that. I think just one current probe, with two wires through it, could do that easily. Again, synchronized complementary 576s.
The 576 also has selectable external inputs for Vertical or Horizontal display (normally from the High Current plug-in). I brought them out to BNC connectors with enable switches. I've used the Vertical input to connect an AM503 DC Current Probe for visualizing tube screen current during curve testing. Probably just what is needed for figuring out those nasty tube kinks.
And, it's even all ready for P type tubes in the future.
Well it still does PNP bipolars and P channel Mosfets anyway. Some P tube emulation circuit could be tested readily.
The one upgrade I still have in mind to do is a second complementary stepper output, for testing differential tube setups. There are several ways to do this.
Easiest would be just an Inverter, or more elaborately a second synchronized step generator board and step amplifier for it, and ultimately a second synchronized 576. That has the advantage of two simultaneous displays, separate offset controls.... And it's already sitting on the bench! ( Thank you $5 relay! )
I read something in the Tek 576 manual once about some sneaky option you get by pressing two step gen push buttons at once. I think it was for just such synchronizing of two 576 units. Have to go find that again.
The other two tube extension I would like to do would be for combining two tubes in Push-Pull. Have to do plate current subtraction for that. I think just one current probe, with two wires through it, could do that easily. Again, synchronized complementary 576s.
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The eTracer I had a while back has the option for pre-heating the tubes at a given operating point. This is also possible with pypsucurvetrace, which also allows idling at a predefined operating point between indivudual readings. This allows maintaining the tube temperature corresponding to whatever dissipation you want.
Nice touch! Clearly the PC type curve tracers are the economical and light weight go-to approach now, especially for anyone who doesn't want to get into electronics mods and fixing problems. The 576 weighs 75 pounds, you don't move them around much. No switching supplies here, just heavy iron.
For the last 20 years though (30 yrs since obsolescence), the Tek 576 has been a very capable curve tracer, especially for the bigger tubes. And not that expensive as a fixer-upper. There are several Websites where these get methodically tested and fixed up. Used parts are available on Ebay. Generally there will be just one show-stopper problem to fix, and then some electrolytic capacitor upgrades and flaky switch/push-button fixes. The Tek manual is superb. With a little ingenuity, I expect these can keep going another 20 years. ( I did get a spare HV CRT supply assembly ) There aren't any Chinese parts in them, but there was a Chinese semi clone of the 576.
For the last 20 years though (30 yrs since obsolescence), the Tek 576 has been a very capable curve tracer, especially for the bigger tubes. And not that expensive as a fixer-upper. There are several Websites where these get methodically tested and fixed up. Used parts are available on Ebay. Generally there will be just one show-stopper problem to fix, and then some electrolytic capacitor upgrades and flaky switch/push-button fixes. The Tek manual is superb. With a little ingenuity, I expect these can keep going another 20 years. ( I did get a spare HV CRT supply assembly ) There aren't any Chinese parts in them, but there was a Chinese semi clone of the 576.
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