Wow, those are really hard to find now. I think I saw one back in 1975 at a surplus store in Kingston NY, P&D Surplus. I don't recall the price, All tubes inside.
TekWiki: https://w140.com/tekwiki/wiki/570
https://w140.com/tekwiki/images/3/3c/Tektronix-570-Outside-Front.jpg
https://w140.com/tekwiki/wiki/570#/media/File:Tektronix-570-Inside-Right.jpg
https://w140.com/tekwiki/wiki/570#/media/File:Tektronix-570-Inside-Left.jpg
Looks like it has up to 10V per step and up to 12 steps. Plate sweep up to 500V at 0.25A avg. and 1 A pk . I don't see any provision to do positive steps for the screen grid, but it does have a regulated screen supply, I guess one could rotate the knob for that to get some feel for g2 curves.
It weighs 75 Lbs too, look at those BIG xfmrs in it. 300 to 500 Watts from the line. (the 576 says 305 Watts from line and weighs 75 Lbs too)
Hopefully your friend can get a manual, if they don't already have one. I wonder if there are any repair websites or You Tube videos for it.
TekWiki: https://w140.com/tekwiki/wiki/570
https://w140.com/tekwiki/images/3/3c/Tektronix-570-Outside-Front.jpg
https://w140.com/tekwiki/wiki/570#/media/File:Tektronix-570-Inside-Right.jpg
https://w140.com/tekwiki/wiki/570#/media/File:Tektronix-570-Inside-Left.jpg
Looks like it has up to 10V per step and up to 12 steps. Plate sweep up to 500V at 0.25A avg. and 1 A pk . I don't see any provision to do positive steps for the screen grid, but it does have a regulated screen supply, I guess one could rotate the knob for that to get some feel for g2 curves.
It weighs 75 Lbs too, look at those BIG xfmrs in it. 300 to 500 Watts from the line. (the 576 says 305 Watts from line and weighs 75 Lbs too)
Hopefully your friend can get a manual, if they don't already have one. I wonder if there are any repair websites or You Tube videos for it.
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Since I have a 2nd working Tek 576 now (bought for spare parts), but without my mods yet for extended grid stepping V range,
I bought one of these new Tek 576 Grid Step Amplifier 10X modules to try out (Ebay pics 1 & 2):
And it works! (3rd & 4th pics of a 10JA5 curve trace here) So it's a simple way to convert a Tek 576 to tube tracing.
However, I would still recommend making a couple of simple mods to the 576. (mods used in the full mod version too) The Screen V needs to turn off when you stop curve tracing a tube. You can do that manually all the time, but eventually you'll forget and take out a tube! This just requires some re-wiring of the DUT toggle switch in the bottom test box (it plugs into the 576, so easy to get to). I used one of the switch contacts, normally used for switching a sense line, to apply screen V when tracing either tube position. We're not testing high current SS here, so it is not needed for tube current wire loss. (it's still re-configurable for high current SS from the exterior front panel via some Banana jacks I installed)
I actually just pulled the box from the other 576 for a quick testing session tonight.
The other issue I see is the lack of a continuous stepping V gain control. You are stuck with the 1, 2, 5, 10... gain sequence from the step control knob on the front panel. Often the curve set will not fill the full screen that way, or runs off the edge. This mod is easy to do also. You just wire a potentiometer in series with the Step Amplifier global N Fdbk resistor to allow a continuous 10 to 1 gain control range. (well I used 10 to 1 for the full mod to extend the range, but 2 to 1 would work fine for the Grid Step Amplifier.)
An alternative mod would be to just put in the mod for 15 steps (from the normal 10). The # of steps is selectable up front, so this is just like a 1 to 1.5 adjustable gain range. Just requires pulling one pin on an IC in the step generator and changing a resistor in the D/A circuit. You'll be happy with the results in any case.
I bought one of these new Tek 576 Grid Step Amplifier 10X modules to try out (Ebay pics 1 & 2):
And it works! (3rd & 4th pics of a 10JA5 curve trace here) So it's a simple way to convert a Tek 576 to tube tracing.
However, I would still recommend making a couple of simple mods to the 576. (mods used in the full mod version too) The Screen V needs to turn off when you stop curve tracing a tube. You can do that manually all the time, but eventually you'll forget and take out a tube! This just requires some re-wiring of the DUT toggle switch in the bottom test box (it plugs into the 576, so easy to get to). I used one of the switch contacts, normally used for switching a sense line, to apply screen V when tracing either tube position. We're not testing high current SS here, so it is not needed for tube current wire loss. (it's still re-configurable for high current SS from the exterior front panel via some Banana jacks I installed)
I actually just pulled the box from the other 576 for a quick testing session tonight.
The other issue I see is the lack of a continuous stepping V gain control. You are stuck with the 1, 2, 5, 10... gain sequence from the step control knob on the front panel. Often the curve set will not fill the full screen that way, or runs off the edge. This mod is easy to do also. You just wire a potentiometer in series with the Step Amplifier global N Fdbk resistor to allow a continuous 10 to 1 gain control range. (well I used 10 to 1 for the full mod to extend the range, but 2 to 1 would work fine for the Grid Step Amplifier.)
An alternative mod would be to just put in the mod for 15 steps (from the normal 10). The # of steps is selectable up front, so this is just like a 1 to 1.5 adjustable gain range. Just requires pulling one pin on an IC in the step generator and changing a resistor in the D/A circuit. You'll be happy with the results in any case.
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I forgot to mention that it only takes 1 of the new Grid Step Amplifier 10X modules to test either of two tubes in the 576 test fixture. That's because of the way Tek did the external interface option Banana plugs, the amplifier gets inserted -before- the tube selector Toggle switch. Very nice. The ability to toggle between two tubes is essential for matching tubes. I wasn't even aware of the External Step Option until this 10X module came along. Tek seems to have thought of almost everything when they designed the 576.
By the way, I peaked under the hood, and the new 10X module is using Analog Devices new 200+ V Op Amp, the ADHV702. There is an evaluation board for it available if you need a +/- 100V Op Amp. (Digi-Key and other suppliers have them) Has incredible specs.
I do plan to do my -full- tube upgrade mods on this later Tek 576 unit (which was originally just for spare parts, until I found it worked just fine! ). So the 10X Grid Step Amplifier won't be strictly needed then. But I have plans for the module yet. I will add an -inverted- phase low level Step Gen output BNC conn. that this 10X module can connect to, for a Complementary Stepper output. This will allow testing 2 tubes simultaneously in Push-Pull configuration. A DC current probe can then subtract the plate currents for display on a separate scope display. (An OT gets added for connecting the two plates to the swept Plate/Collector test terminal.) This will provide a graphic display of the resultant P-P summed currents usually shown in text books with a flipped around set of plate curves and regular plate curves offset by biasing. Biasing, Screen V, and Plate V can then be optimized for best P-P operation.
But until then, its already working as a good 2nd tube curve tracer. Here is the JJ KT77 tube, curve traced using the 10X Grid Step Module on the second 576:
Very nice curves. Look how evenly spaced. You won't be seeing any significant 3rd harmonic in a P-P amplifier with these tubes.
By the way, I peaked under the hood, and the new 10X module is using Analog Devices new 200+ V Op Amp, the ADHV702. There is an evaluation board for it available if you need a +/- 100V Op Amp. (Digi-Key and other suppliers have them) Has incredible specs.
I do plan to do my -full- tube upgrade mods on this later Tek 576 unit (which was originally just for spare parts, until I found it worked just fine! ). So the 10X Grid Step Amplifier won't be strictly needed then. But I have plans for the module yet. I will add an -inverted- phase low level Step Gen output BNC conn. that this 10X module can connect to, for a Complementary Stepper output. This will allow testing 2 tubes simultaneously in Push-Pull configuration. A DC current probe can then subtract the plate currents for display on a separate scope display. (An OT gets added for connecting the two plates to the swept Plate/Collector test terminal.) This will provide a graphic display of the resultant P-P summed currents usually shown in text books with a flipped around set of plate curves and regular plate curves offset by biasing. Biasing, Screen V, and Plate V can then be optimized for best P-P operation.
But until then, its already working as a good 2nd tube curve tracer. Here is the JJ KT77 tube, curve traced using the 10X Grid Step Module on the second 576:
Very nice curves. Look how evenly spaced. You won't be seeing any significant 3rd harmonic in a P-P amplifier with these tubes.
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Ummm, well -35 dB at 200Vp-p is 0.03%, would likely beat many tube driver stages. Must be running out of Gain-BW at 200Vp-p though.
50Vp-p drive at -70 dB is looking good. At least up to 10 KHz.
-70dB and 3 KHz is more than fine for curve tracing.
I actually leave a little biasing squiggle in the modded step amplifier, so I can tell when zero grid Volts is being crossed when adjusting the continuous Offset dial.
50Vp-p drive at -70 dB is looking good. At least up to 10 KHz.
-70dB and 3 KHz is more than fine for curve tracing.
I actually leave a little biasing squiggle in the modded step amplifier, so I can tell when zero grid Volts is being crossed when adjusting the continuous Offset dial.
