Tektronix 570 Curve Tracer

Transcript

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sometimes life is well unpredictable and
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sometimes things just seem to be the way they work supposed to be what you see on
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the screen is a trace of a pentode
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vacuum tube it is being displayed on a
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Tektronix model 570 characteristic curve
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tracer so what do those two have how do I know what time that was two together
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well I wanted to return to I wanted to
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wait one more video and I wanted to
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return to electronics if I could as many of you know I've been off doing some
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kind of wrapping up a review of my astronomy hobby and things like that but
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my second love chronologically that is
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was electronics I started out with astronomy and chemistry but because I
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got a telescope and a chemistry set when I was 9 but by the time I was in middle
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school they called it junior high back then electronics was the thing that I
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loved the most and of course being in the 1950s that meant vacuum cubes well
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Oh a couple of weeks ago my UPS delivery
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man stopped me I was out in the front
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yard as he was delivering something and said you're interested in vintage
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electronics tubes and things like that aren't you and I said yes I wondered why
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he how he knew that turns out he has delivered so much thanks to me that he
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knew it and he also had a background in electronics he had worked for Raytheon
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back in I think in the in the eighties
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doing some electronics work and so he said you wouldn't be interested in an
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old Tektronix curve tracer would you I mean my eyes lit up it was like you know
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it would be like asking the Albert Einstein I'm no Einstein but like asking
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Albert Einstein would you be interested in relativity yeah so he sold me this
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curve tracer and I've been playing with it for the last week or so and so it is
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I think fitting has a return a video
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return to electronics and so you know if
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I had to if I had to close out in on anything this would be it at any rate
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enough about me in the history in my UPS man what this device does is it displays
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various current and voltage characteristics graphically along the
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the vertical axis it displays the current through the tube and along the
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horizontal axis it displays the voltage in this case it's the play current verses play voltage and the
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stamps are varying grid vote values so let me show you the block diagram of
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this device and then come back and show you how it works a little bit and and
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then we'll do we'll run a couple of tubes on it and see how it how it works
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now it has a neat feature that it allows you to switch quickly between one tube
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and another tube I'll save for later who of what those tubes are but these are
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two pen toads that are being displayed and you see there's a difference in that
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one and in that one though there's not a lot of difference notice that the top is
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very close to the the top trace of this one so let's take a look at a block
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diagram so here is the block diagram of the Tektronix 570 by the way this device
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was built in 1955 I was 10 years old on
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the left is a is the shaper for the
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stepping voltage you remember you you saw that it would step the grid voltage it starts with this stepping voltage
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shaper that feeds a step generator then
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that is amplified by the step amplifier and can be applied to the grid of the
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tube this is the device under test and there's space for two of these so that
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you can switch between them well look at that a little bit later the so for the
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display we just saw the step is applied to the grid the cathode is grounded the
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plate is connected to the horizontal amplifier and also to the plate sweep
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generator now the what the plate suite generator does it generates a a sweet voltage that can
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go up to I think 500 volts on the 570 so
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so it can be anything as little as 1 volt let's see it's the no 5 volts it's
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the traditional Tektronix to 510 so it's 5 10 20 50 a hundred two hundred five
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two hundred three hundred five hundred volts so it applies that to the plate
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and then you can read out the plate through the horizontal amplifier while
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the the current through the tube is
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measured by the let's see vertical amplifier and the way it does that is
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the current through the plate sweep generator is flows through this resistor
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and so it taps the voltage off of that so this allows you to measure plate
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current on the vertical while measuring plate voltage on the horizontal and
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that's the display we just saw a minute ago so this is the basic diagram of the
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five seventy so this is a printout from
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the five seventy manual showing the
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plate current versus plate voltage and
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in this case this is for a six u 8 now a six u 8 is a two section tube it looks
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like this
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notice that one section is a triode and one section is a pentode let me let me
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just pick that up and take it a little closer to the camera so that you can see
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a little better what that looks like so you see that it's a yeah it's a triode
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on the right and a pentode on the left these tubes were used in early
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television sets to generate the vertical
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sweep the triode section was used for the oscillator and the pentode section
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was used to drive the yoke I'm not going to get into television Theory here but
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basically that is the way that the the signal would be swept across the screen
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from top to bottom there was also a horizontal sweep system that would sweep
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it from left to right so what you see here are a series of stamps and on the
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left are the setups for this so in the
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manual one of the things that they part of the training of someone on using the
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570 was to set up a 6u 8 and by the way it even I think originally came with a
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68 tube fortunately I have some new old stock tubes and was able to dig up a
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couple of 6u eighths but the basic idea
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of this is it allows particularly a design engineer to measure the
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characteristics on a particular type of tube it also allows someone to compare
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the characteristics of two tubes for example suppose that you have a dual
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triode like a 6s n7 where there are two triodes in the same package well you can
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switch between those two using the switch that I used earlier and
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compare to see how well matched they are so there were basically two applications
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for this device one was for design engineers who were designing tube circuits to be able to find out the
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characteristics of the tubes they were using so that they could design the
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circuit around those characteristics and the second which has come into even much
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more use these days is the matching of
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tubes the because of the resurgence of
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vacuum tube amplifiers both for guitars and for high fidelity the need to match
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tubes particularly since you're dealing in many cases with new old stock tubes
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that have been around for 50 60 70 years is finding a pair of tubes for example
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that have similar characteristics so that they they don't require a lot of
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imbalance in the amplifier to work correctly so for example in a push-pull
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stage output stage and if you want to know more about that there are some
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videos I did on how tubes work and and vacuum tube circuits that you might want
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to look at at some point but at any rate these days these are used by places that
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specialize particularly in tube electronics generally amplifiers to
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match tubes and do other things for me I was just it's just a toy and I'm glad I
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was able to acquire one of these it's almost like it was it was ordained here
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you see the characteristics of a triode what we looked at just a minute ago was
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the pentode section this a triode of a six gh8 - if you look on
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the left at the pinout you see it is and I don't expect you to remember the six
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u8 but take my word for it it is exactly the same pinout as the six you ate the
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six gh8 was the replacement for the six you ate it had a little more
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transconductance and could handle higher voltages so the six GH 8 and the six you
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ate that we saw a minute ago are both medium mu triose mew just means the
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amplification factor and a sharp cutoff pentode so these are what you would
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display for the triode section of that same cube so let me show you a little
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bit about how the 570 is set up and then we'll talk a little bit about how you
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might use something like this though I will admit this is really just a boat
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anchor okay there there is an application for it in in tube matching
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for amplifiers but frankly there are solid-state versions of these kinds of
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things that can be done and they work better because they work on a computer
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so you can log the data and analyze it better and so on but for for a dinosaur like me to come
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across one of these things is sort of the find of a lifetime they are very
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expensive on YouTube I saw one a bay I saw one that I looked for and by the way
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the the UPS delivery man and I had quite a long discussion several times I said
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do you realize how much these might be worth and he said yeah but I just don't want to pack the thing up so if I could
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just deliver it that's what I would like to do and sure enough he showed up with it and and my
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one of my dreams of a lifetime came true so I said I'd get away from me let's get
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back to the five seventy and a little bit about how you set this up here is
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the rat's nest patch patch cords
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whatever you want to call it that you set up a tube with along the top you see
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are a series of binding posts on the left are two for heater same on the
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right let me move this turn this to get a little better light on that there we
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are then there are crowns for the cathodes and notice these are symmetric
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then there is grid a and grid B there is
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a minus voltage that you can apply to the Tobias that you there is a plus
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voltage and this is the one place where they are so it begins to be asymmetric
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there is a plate connection and there is a minus DC connection so what are all of
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these for well the grids are the step voltage that we talked about earlier the
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the plate is where you read the plate voltage and the plate current the DC
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plus is to allow you to bias the screen grid for example of a pinto tube and the
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DC minus is in case you need to bias a APN on a tube to a particular level as
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well as the - 150 27 K which has a kind
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of special function that I'm not sure if I'll get into all of that
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but on the face of the 570
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on the right you get a little more light
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on this well something like that you see
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on the right here is a voltmeter that you can select and down below is what it
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shows and it allows you to adjust the heater voltage the positive and negative DC voltage as well as the range of the
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meter then below that let me readjust
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this tripod beneath the meter is the
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step generator and you notice that it allows you to either do 120 or 240 steps
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per second and you can adjust with the red knob the number of steps per family
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I'll show you that in a second on the right is the volts per step and the
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start adjust in other words where that step voltage starts normally you want it to start at zero and you notice that
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there is a little zero marking right here where where this is set right now
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beneath that is the CRT display it
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adjusts the vertical and horizontal sensitivity as well as the vertical and
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horizontal position down here moving to
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the left pardon the moving the tripod here you
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see at the very bottom is the adjustment for the minus DC voltage above that or
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the operating voltages you can set the heater voltage for anywhere from about
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1.2 volts up - I think it's 117 volts so
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pretty wide range of heaters and it adjustable so for example you can run a tube at below or above its normal heater
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voltage to see what that does to the characteristics the this is the control
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for setting the positive DC voltage like for example the screen grid it has both
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a step and an adjustable and by the way this is sort of the traditional Tektronix layout they used for decades
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there while this is a specialized oscilloscope the the main the bread and
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butter of Tektronix were their general-purpose oscilloscopes and they
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used this same basic control setup so once you learn how to use one Tek you
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could use another above that is the
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plate sweep generator that you notice allows you to set the peak volts up to
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500 volts and to adjust the size of the series load resistor finally over here
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is the mains odd to now turn on and you
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notice a little bit of a sound from the fan then you can turn on the test
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voltage and and the reason for this switch is so that there is no voltage on
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this test panel until you're ready for it so in other words you don't have to
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move these wires around while there's voltage on the on the test panel so now
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we're going to turn the test on and you may notice up here
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on the meter it now shows a hundred volts is the plus DC voltage I have it
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set to the plus DC position so now let's
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move this tripod up a little bit turn off some of this light
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and turn up the intensity and turn on
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the grid grid a then and what I'm doing
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is I'm flipping this switch down here from the grid a position to the grid B
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position I know you can't see that because of the glare from these pilot lights but here is grid a that's one
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cube here is grid B and you notice there's a setting in between for 0 what
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that is doing is switching between the grid of this tube and the grid of this
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tube or in the case if you wish you can have two grids of the same tube like a
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dual do dual triode where there are two triodes in the same section and it all
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depends on how you have these wires set up so that is basically how the 570
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works and how you operate it I'm I'm not
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going to go through an extensive you know showing a bunch of different tubes and all of that I'm not sure what
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purpose that would serve though I do realize a few people might be interested in seeing their favorite tube on a 105
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70 but instead what I'm going to do is talk a little bit about some small
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changes that I made to this to this 570
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that improved its performance a little bit
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and one thing the of course they needed
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a cleaning and I cleaned out the interior pretty well vacuumed out as
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much of the dust as I could get cleaned the tubes off and did a pretty good cleaning on the switches and other
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things basically the same thing you do anytime you're restoring a vintage piece of equipment other than that it the the
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unit worked right off the bat so but it had a few quirks and fortunately I was
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able to find and remember a few of the little changes and so things that people
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have done over the years and one of them I'll show you on the schematic take
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Tektronix normally did a wonderful job in fact their equipment was over
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engineered but on this 570 they did make one little design error and and so let
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me show you how I fixed that and since then this unit has performed beautifully
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this is the schematic of the step amplifier in other words the the
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amplifier that takes the the step voltage and buffers it amplifies it and
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provides it to the grid a grid B switch that you see here so let me zero in on
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this part of the schematic so this is
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the final power stage of the step amplifier it consists of a 6c l6 pentode
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and you may notice that the plate is driven directly off the minus 400 volt
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unregulated supply and the cathode is driven through this 120 K resistance 300
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volt unweighted so plus 400 on the plate - 300 on the grid on the cathode
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resistor and then this is a cathode follower the so the signal comes out of
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there and is switched by this grid a grid B switch to the grids of the tubes
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well one of the problems that this stage has is the unregulated supply is located
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a long way away from this 60 l6 and because it does draw a very fairly
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high currents it can it can oscillate
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now early on I think the tech engineers thought that the oscillation was due to
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parasitics in the pen in the test panel of the patch panel and so they released
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some resistor jumper wires to try to
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suppress that and that still does sometimes happen with certain particularly high gain high frequency
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tubes tubes fused for example at UHF frequencies back in the day but the real
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problem with this wasn't it was the decoupling of the minus and plus
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unregulated supplies so all that I needed to do was to add a capacitor very
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close to this tube from the minus regulated and I used to point to 2 micro
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farad you could use a bigger or smaller one just be sure that the voltage rating is sufficient between the minus supply
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and ground and the plus supply and ground and that cleans up the the what
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appears to be oscillation on the grid signal which of course also appears on
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the plate once you have changed the circuit to do that this particular unit worked perfectly
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now there were a few other little issues with the 571 I've already mentioned the
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fact that some tubes would oscillate and and that you could help that by
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suppressing the grid let's go back to this picture here the connection between
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this point and the grid could be replaced by a small resistor patch cord
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that would it's basically called grid suppression and the resistor is often
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called with suppression resistor it was a common way of getting rid of parasitic
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oscillation in tube circuits it's still used in transistor circuits today there
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there are times particularly with MOSFETs where you have to insert a small resistor in the gate lead to keep the
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stage from oscillating but except for
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those a couple of small things and a little bit of maintenance and a little bit of recalibration I was able to get
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this 572 work and it was pretty much working when I got it it just needed a
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little perking up don't we always at our age so oh I think what I'm going to do
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oh I did want to mention something that before I before I finish and that is
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that the plugins that it comes with it
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comes with the pair of octal plugins I'm using the nine pin up plugins right now
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for the the tubes that are in there it comes with a pair of seven pins logins
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it of course comes with a series of patch cords and things of that sort but
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one thing it doesn't come with is a way to do the characteristics of octal tubes
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now back in the day the most prominent tubes were octal
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seven pen and nine pen but Philco partly
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just to get around patent restrictions came up up with a tube type that they
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called a lock ttle let me show you one of those here it looks like this notice
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that there's a small indentation there
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in the in the locating pin other than that it basically is an octal tube these
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pins are smaller physically but they're the same eight pm configuration that oh
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but there's no way to test these or to display these characteristics on the 570
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but there is an easy solution to that and that is if you take a I'm gonna get
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one of these over here if you take an octal tube base that you can buy these
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are very readily available today and you
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pair it with a lottle socket now all that is all that's inside this is just a
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wire from that pin to that pin all the way through in other words eight wires
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just going straight through from side to side and then pull through on the other
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side and soldered but what that allows you to do is to test our lock dual tubes
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which sort of completes the collection
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from the day now if you want to test newer tubes you can do so the problem is
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that the most pins that any of these sockets have is 9 p.m. so if you try to
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display a compact Ron for example you're going to run out of pins if you try to
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connect all of the pins of a John because that has 12 or an O var
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that has 12 pins and there's only a total of nine pins available on the 570
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but you can still do it using the same
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technique you just need to be clever about the or Frugal maybe in the way you
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use your connections so that is my
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experience with the Tektronix type 570
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characteristic curve tracer I hope you've enjoyed this and I hope you've
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enjoyed my other videos at any rate I do
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hope that things will go well for you in the future and look forward to getting
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through this Corona thing civilization will endure and and so I know that
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there's they're happy futures ahead at any rate for now I want to say thanks
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for watching

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