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Old 3rd Feb 2018, 1:24 pm   #41
MrBungle
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Default Re: Tektronix 465 restoration

Random flashback .... When I was at university, our linear systems lecturer explained to us that everything is analogue and Fourier was at the root of all things. A physicist popped up and disagreed. Followed by the digital systems lecturer siding with the linear systems lecturer. This resulted in a twenty minute to and fro about digital ontology which diverged into all sorts of horrible things. No one was enlightened but we were thoroughly put off learning anything more about any of the subjects and crawled back to our halls and just read The Art of Electronics instead, which had a strict opinion of avoiding such philosophical or technical debates and get back to designing circuits empirically and avoiding mathematics or thinking problems over too hard
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Old 3rd Feb 2018, 2:04 pm   #42
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Default Re: Tektronix 465 restoration

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So, before this thread gets closed on account of 'topic drift', can we return to this thread's subject, please: Tektronix 465 restoration?
Anyone?
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Old 3rd Feb 2018, 2:43 pm   #43
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Default Re: Tektronix 465 restoration

I suppose I better pipe up. Cleaned it thoroughy and calibrated it. Timebase was a tiny bit out. One of the timebase cal trimmers was munted by a previous heavy handed calibration monkey. I replaced it with a modern bourns part. Looks and works as good as new!

Came with a load of probes so I have assembled a working set of Tek probes at last.

After an Hp6236B power supply now and I’m in analogue heaven.
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Old 3rd Feb 2018, 4:09 pm   #44
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Default Re: Tektronix 465 restoration

Now you're up and running, you'll find the 465 a very nice scope to use, and 100MHz bandwidth is enough for plenty of work. I use a 465B in the shack and I have a spare as backup. If I need something for higher frequencies, for radio work, I switch to the spectrum analyser. There's a 1GHz digitising scope on the to-fix pile, but it's sat there for a few years with no needy job to push it up the queue.

By the way, the old HP power supplies are nice and quiet, but they have a major design flaw. You don't get to see what the output voltages are before you apply them to your circuit if you turned it off and left it for a while. If ank knobs got knocked, you risk damaging what you're working on, or else you have to disconnect your wires, turn on, check the meters, and finally reconnect. Before HP bought the firm, the power supplies were by a firm called Harrison (of Noo Joysy)

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Old 3rd Feb 2018, 4:41 pm   #45
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Default Re: Tektronix 465 restoration

Indeed. I’m not going to be using this for much RF work past power measurement. An SA will be added when one turns up at a reasonable price. I might be riding an electric unicorn before then.

Yeah I’ve got the later version of the HP supply already, the E3630. I have learned that all knobs left before power up. My TTi supplies are much better in that respect but take up a ton more space.

Found a 6237B in Spain for £120 which isn’t too bad. That has a 0-18v 1A tertiary supply.

I’m favouring simpler equipment these days.
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Old 3rd Feb 2018, 5:03 pm   #46
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Default Re: Tektronix 465 restoration

Knocked up a curve tracer with an AC wall wart and a 1k resistor.

Vertical = 1ma/div. horizontal = 1v. 4.3v Zener.

Really can’t beat a tek for clarity!
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Old 3rd Feb 2018, 5:07 pm   #47
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Default Re: Tektronix 465 restoration

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By the way, the old HP power supplies are nice and quiet, but they have a major design flaw. You don't get to see what the output voltages are before you apply them to your circuit if you turned it off and left it for a while. If ank knobs got knocked, you risk damaging what you're working on, or else you have to disconnect your wires, turn on, check the meters, and finally reconnect.
Wow - I had to look up the E3630A and check that for myself!

I find it astonishing that an adjustable bench power supply makes it out into the market with no DC output switch - let alone one wearing a HP/Agilent/Keysight badge I also note that the current limit isn't variable, which is another surprise.

You live and learn. Those old Thurlby PSUs might be a bird's nests built into old biscuit tins, but they have got the basics right and they are pretty reliable
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Old 3rd Feb 2018, 5:18 pm   #48
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Default Re: Tektronix 465 restoration

It has hefty foldback limiting so if you do anything stupid it hangs up the current. Really the engineering in it is top notch I will say. Haven’t blown anything up with it yet. Pricing is ridiculous though! Didn’t pay much for mine.

Problem is it’s three power supplies, two tracking in one tiny little box with no fan noise. My two thurlby supplies (pl330+pl154) take up a hell of a lot of room (5x the volume) which I don’t have at the moment so they get relegated to high risk tasks or where I need a bit more oomph (rarely) or where I run out of power supplies (regularly!)
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Old 3rd Feb 2018, 5:38 pm   #49
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Default Re: Tektronix 465 restoration

Looking at the schematics, only the 6V output is foldback; the 20V outputs are CC.

I can't argue with the form factor - the Thurlby units are big old beasts

Even though I'm really tight for space here, I have to accept that's just physics. If you want a fanless PSU, or one that doesn't rely on a potentially (electrically) noisy SCR pre-regulator, or a (definitely) noisy switched-mode job, then it'll occupy space. Of course, being only 0.5A on the 20V rails helps - but that's a fair compromise for most work - that sort of PSU is ideal for op-amp circuitry, etc.

Another thing to watch for - if the +20V rail goes into current limit, the -20V rail will fall in sympathy. However, the opposite is not true - if the -20V rail goes into current limit, the +20V rail will stay put. That's because the +20V rail is the reference for the -20V rail. Now, this is pretty common for split power supplies like this (the same is true of a PL320QMD in tracking mode), but it can be the source of much confusion! Decades ago I built a dual PSU that didn't have this problem - it's not my finest work, and it's probably only 95% finished after all these years, but it does work well for what it is. Perhaps one day I'll get around to completing it...
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Old 3rd Feb 2018, 6:09 pm   #50
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Default Re: Tektronix 465 restoration

Exactly. Went for the compromise here with the preregulator. I like the Chinese supplies for one thing; they tend to skip this and use a relay which switches taps after sampling the output voltage via a comparator. Simple elegant solution. Unfortunately they tend to be idiots and make it fail high voltage which burns out the pass transistors. Most of the time you’re not doing anything that require switching this relay so it usually works pretty well. Mastech HY1803D I’m looking at you.

Interesting point with the tracking. One I wasn’t aware of.
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Old 3rd Feb 2018, 11:24 pm   #51
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Default Re: Tektronix 465 restoration

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Originally Posted by Radio Wrangler View Post
If I need something for higher frequencies, for radio work, I switch to the spectrum analyser.
I would strongly recommend the now vintage Tek 2465B for RF work. There are a lot of reasons. Its bandwidth is 400MHz, but it will sync lock and view a 900MHz wave from the SG504, so it can visulize a wave at that frequency even though the amplitude is not meaningful. But that is a testament to its trigger circuitry too.

Also, although the signal processing is analog (which is the only kind of scope I care for) it has many digital features with cursors to display amplitude, time, frequency and many memory functions. The CRT's in these scopes are a jaw dropping masterpiece of Electron Optics, that reached a peak of design & build perfection and I think the world will never see anything like this again. The CRT alone would probably cost 3 to 5 times as much to make as one entire new 400MHz modern digital scope with a flat colour screen. This CRT cannot be beaten for waveform reproduction by any digital scope.

The 2465B is called by some "Tek's last repairable scope" because it was well supported by its manual and diagrams and is relatively easy to service.

For the most part, there are only three or 4 problems that these scopes suffer from which are generally all repairable; leaked surface mount electros on the A5 board in some versions, power supply electros, sometimes a deflection IC fails sometimes (not in my units) and the battery powered Dallas NVram failing due to internal battery failure.

For the latter NVram issue I have solved all the problems with that by using Ramtron non volatile ferro-electric rams and dumping the Dallas NVrams. The link to the article showing how to do this is in post #30.

Last edited by Argus25; 3rd Feb 2018 at 11:29 pm.
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Old 4th Feb 2018, 12:29 am   #52
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Default Re: Tektronix 465 restoration

My main 'scope is a Tek. 2465: one of the best 'scopes I've ever used. The ability to measure freq., period and amplitude of the displayed waveform with its variable-position cursors is really useful. However, mine does need a new fan - it is a bit noisy. Once, I did remove the case covers to see what was involved in replacing the fan - expecting something relatively easy. Boy, was I wrong! So I'm living with a slightly noisy fan for now - but I am aware that fan failure in a 2465 can have dire consequences for the bespoke I.C.s on the lower pcb. However, since the fan is slightly noisy, I know it's working. When I suddenly can't hear it, I'll switch off the power el pronto!

Al.
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Old 4th Feb 2018, 12:40 am   #53
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Default Re: Tektronix 465 restoration

It's the same fan assembly as the Tek 465/475 but with a different chunk of plastic hanging off the shaft. You can actually just eviscerate it and stick a good old fashioned PC style fan on the back of the chassis.

All those ASICs scare me away from such a beast.

Edit: before I forget, the main cause of the fan to stop spinning I found was that the IC was duff that controls it. Quite surprisingly the IC turns out to be a simple transistor array based on 2n2222's. Just do a diode test on the IC, find the duff transistor, snip the pins off for it and solder another discrete one in the holes over the IC and it'll probably just work again. I have done this twice now.
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Old 4th Feb 2018, 11:50 am   #54
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Default Re: Tektronix 465 restoration

The fan appears to be integral with the PSU and deeply buried within it. On inspection, a lot of dismantling appears necessary to remove the PSU in order to remove & replace the fan. Later 2465 'scopes do feature a PC-style fan: this 'scope uses the earlier turbine style. To replace that fan with the later type, the entire plastic housing at the rear of the 'scope will need to be replaced.
It's a pity that Tek. chose to make fan replacement such a difficult task.

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All those ASICs scare me away from such a beast.
I share your sentiments on that. But you have a 2465B: doesn't that use the same (or similar) array of ASICs?

Al.

Last edited by Skywave; 4th Feb 2018 at 11:55 am. Reason: Ad quote, etc.
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Old 4th Feb 2018, 1:44 pm   #55
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Default Re: Tektronix 465 restoration

Quote:
I share your sentiments on that. But you have a 2465B: doesn't that use the same (or similar) array of ASICs?
His 465 is much older than the 2465B, so none of those troublesome ASICs. Probably a handful of custom Tek parts though - and IIRC there's a tunnel diode or two in the timebase.

Whenever the 2465B is mentioned, I feel the need to put in an "honourable mention" for the Philips PM3295. This is 350MHz (the A model is 400MHz), but has a nicer user interface than the Tek. The display is much sharper and brighter - probably because it has a 24kV acceleration potential (compared to 16kV for the 2465B). But best of all, Philips didn't cheap out when choosing the shift registers for the front panel LEDs, so they don't all flash at once whenever you press a button

We've had several ASIC failures on the Tek models - and disappointingly, Tek weren't able to help us, despite the units being relatively new and not long out of production. Whereas the custom Philips ICs and thick-film units appear to be very reliable indeed - I've yet to hear of a failure. The Philips unit is definitely easier to work on, and doesn't have guaranteed built-in obsolescence in the form of those Dallas battery-backed RAM modules.

Much as I initially loved the 2465 series, the Philips has won me over by just doing its job well with 100% reliability. I can even forgive the fact it's got a brown front panel
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Old 4th Feb 2018, 2:38 pm   #56
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Default Re: Tektronix 465 restoration

The main competitor to the Tek 465 came along a little later. It too has a few custom hybrids in the signal path but is still quite repairable. On the plus side it doesn't have a fan and doesn't need one. Access inside is also an awful lot better. Performance is similar, trace focus is usually a bit better. It misses out on a couple of less-used functions the Tek has.

They never had the popularity of the Tek because an earlier model had a terribly ticklish trigger circuit based on a tunnel diode. As a consequence th HP brand got a bad reputation in scopes. The 1740A competitor to the 465 was designed by people who understood what had gone wrong with the 180 series, and they designed the 1740A with fast ECL logic controlling the timebase. Despite this, the reputation lingered, although no longer with any foundation.

The reputation still lingers and if you look around you'll come across 1740A scopes a lot cheaper than 465 scopes. If you believe the legend, you have to buy the Tek. If you don't, then you can have a bargain, and a quieter workshop.

Yes, I have a pair of 465B's. They were what was available when I was looking, but since then I've collected some 1740A's. Either model will do me.

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Old 4th Feb 2018, 3:16 pm   #57
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Default Re: Tektronix 465 restoration

Yes, I have a 1740A restoration on the go here, albeit rather sporadically. I have no real excuse for not finishing since finding a spares donor, thanks to the kindness of people on this forum. I would agree that the trace is sharper than the 465, and the lack of fan not only means they run silently, but the insides are always spotlessly clean. As mine has been sat around in pieces for so very long, the PCBs are now very dusty, and I know I'll feel compelled to clean them scrupulously before finally putting it back together
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Old 4th Feb 2018, 3:43 pm   #58
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Default Re: Tektronix 465 restoration

I’ve had a 1740A. I didn’t like the flood gun illumination, the timebase switch arrangement or the hybrids. Otherwise a nice bit of kit.

The main reason the 4x5’s get dirty inside is running them without a filter.
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Old 4th Feb 2018, 5:35 pm   #59
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My secondary 'scope is an HP 1715A. I've always regarded it as HP's competitor to the Tek. 475: both claim a 200 MHz B/W.
I rarely use that 1715A; I seem to recall that the triggering was a bit 'iffy'. A few years ago, when I took the covers off to have a look inside, (with the triggering problem in mind), I think I recall seeing a three-dimensional arrangement of main cct. boards, interconnected by board edge contacts and edge connectors, making measurements (with the power on) at many circuit points impossible. So I put the covers back on - and left it alone.

Once upon a time, I did own a variant of the 1715 that had a 'memory CRT' (can't recall the correct name as I write this - but you'll know what I mean). The internal construction was same as the 1715A. It developed an intermittent time-base fault, so I sold it cheaply, with that fault declared.

A few years ago, the EHT xformer in one of my (then owned) Tek. 475's failed. I sold that relatively cheaply, too. It was transported by a well-known courier, who decided to smash the CRT whilst being transported. A full refund to the buyer resulted in a significant financial loss.
Many, many years ago, I too owned an HP 180 'scope. What I liked about that was the really large CRT face. The EHT module failed in that too, rendering it B.E.R. (HP gave me a quote for that part: more that £700! )

When I bought my Tek. 2465, I made a point of undertaking a long journey to look at it, see it working and transport it myself: on test, it was O.K. So I returned home with that 'scope and £300 lighter!

Al.

Last edited by Skywave; 4th Feb 2018 at 5:50 pm. Reason: General tidy-up.
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Old 4th Feb 2018, 8:01 pm   #60
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Default Re: Tektronix 465 restoration

I’ve got a rule of never transporting a scope by courier. My tek 2225 was damaged by the courier. Managed to smash one of the moulded plastic feet to bits. That didn’t work when I got it either. Got a nice refund out of it though. Think it cost me about £50 including the small pile of capacitors it ate and a new set of Wittig probes.

The last four Tek units I’ve had involved a reasonable drive. Worth it as no one knows how to pack things properly. Not paid more than £31 each for all of them either (465, 3x465B, 2x475). I’d still have them if I didn’t get funny looks from SWMBO regarding the growing collection.
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