Tektronix 465 restoration

[MrBungle]

I recently obtained another scope. Finally a decent analogue unit. I had a Philips PM3217 described previously that blew up, followed by a Rigol unit which I just didn't get on with and managed to get a Tektronix 2225 to fill the analogue gap. I didn't much like this. Didn't feel very solid and the controls were cheap and nasty. Numerous 465/465b/475 units have crossed my hands in the last couple of years but all were a battle and a half to get operational so I didn't fancy keeping them as friends. Opportunity came the other day to grab a Tek 465 in reasonable condition but dead as a dodo with no display so I took it. Turned out to be a "unicorn".

Got it, dragged it home, found two shorted tants and a popped fuse, replaced them with a couple of electrolytics (and the correct fuse!) and it sprang into action. Calibration was slightly out on timebase which has been sorted (against a calibrated DDS generator) and that was it.

I've started cosmetic restoration but so far looking good. I've kept the photo rather limited as they're the only bits I've cleaned so far

Unit is dated 1974 so is 44 years old. It has 100% original everything in it including capacitors. Has never been opened, no meddling and is immaculate inside! Trace is sharp as anything. Apparently the previous owner had it in dry storage for 30 years!





Very happy with this one

Best feature of course, compared to Philips, is no RIFAs to be seen.

[Radio1950]

Those Tek 465s are excellent with very good trigger flexibility and a great Delayed TB.
Not bad for ATC RSR and SSR radar system servicing.
Also used one of these with CEPT32 PCM.
mike

[Craig Sawyers]

Nice scopes. I have a 475A with DM44, and is one of the go-for scopes in the stable. Even hauled it to London some years ago on a project I was doing at that time. Got some funny looks on the Underground!

[Boom]

I have a 475A which I rarely use but it's there if I need it. The 475A is good for 200MHz and it's quite something to see a 200MHz trace being fm'd.

The only problem it has had ever since I have had it is that the calibrator runs slightly low at about 995Hz. I don't have the circuit but a quick look seems to say that the calibrator is just a discrete squarewave generator with no adjustments at all. One day I might sit down with it and sort it out. Then again I might see if I can justify a new fangled digital device.

[MrBungle]

I like the 475. The only problem is due to the vertical having a veritable ton of bandwidth the trace is fuzzy as anything even with the 20/100MHz BW limits switched in. I think I read somewhere that the designers got the vertical amp final IC design a little wonky.

Very nice range of scopes. Really want to get my hands on a 485 or 454A now to go with it. 454A notably being the last scope they did without any ICs in it at all.

[Skywave]

Originally Posted by Boom

The 475A is good for 200MHz and it's quite something to see a 200MHz trace being fm'd.

Yes, you can see a 200 MHz trace, but you can't measure its amplitude, since the 475 is -3dB in its response long before 200 MHz. And then there's the B/W of the probe to consider.

Al.

[MrBungle]

The 475 I had for a few weeks for repair measured up at about 245MHz of bandwidth (based on rise time from an avalanche pulse generator). Was quite impressed. Had to terminate the entire thing with a through terminator literally on the front panel to get that though. PG was from Linear AN47 built in a Pomona inline box and using a BSX20 transistor.

[Craig Sawyers]

Originally Posted by Skywave

Yes, you can see a 200 MHz trace, but you can't measure its amplitude, since the 475 is -3dB in its response long before 200 MHz. And then there's the B/W of the probe to consider.

There must have been something wrong with your 475. I've just checked mine using a certified 34ps rise time pulse generator, via a wide bandwidth 50-ohm load. I measure an aberration-free 10-90% rise time of 1ns (0.01us sweep range with 10x multipler). That suggests that the bandwidth is 350MHz.

Pulse generator from here https://leobodnar.com/shop/

[MrBungle]

I will say that I noticed that the bandwidth on mine improved by about 40MHz when I tightened up all the screws on the front end attenuator assembly on mine. Every Tek scope I've had has loose screws. In fact I noticed they forgot to screw the interface board down in this 465...

[Craig Sawyers]

I must check the sweep cal and x10 on mine, because 350MHz is just too high, even with Tek's conservative specs.

[AC/HL]

One post moved to a new thread: https://www.vintage-radio.net/forum/...d.php?t=143543

[Skywave]

Originally Posted by Skywave

Yes, you can see a 200 MHz trace, but you can't measure its amplitude, since the 475 is -3dB in its response long before 200 MHz. And then there's the B/W of the probe to consider.

Originally Posted by Craig Sawyers

There must have been something wrong with your 475. I've just checked mine using a certified 34ps rise time pulse generator, via a wide bandwidth 50-ohm load. I measure an aberration-free 10-90% rise time of 1ns (0.01us sweep range with 10x multiplier). That suggests that the bandwidth is 350MHz.

Two points:
1. It was not 'my' 475. I quoted the manufacturer's specifications: 1.75 ns rise-time.
B/W (Hz) = 0.35 ÷ rise-time (seconds).
Therefore, B/W = 0.35 ÷ 1.75 ns = 200 MHz.

Note that the 'bandwidth' of 'scopes is always where the response is -3 dB of its mid-freq. band value.
For a Tek. 475, the -1 dB point will be probably in the region of 80 → 120 MHz.
For serious level measurements, it's the -1 dB freq. - or less - that limits the useful range.

2. There is absolutely no way you are going to obtain a -3dB B/W of 350 MHz with a Tek. 475!

I suggest that instead of making a pulse-type measurement, you use an analogue source with an accurately calibrated attenuator and an accurately calibrated freq. scale - something like an HP 8640B.

Al.

[Craig Sawyers]

Thanks for the tutorial. Gosh - you must think I'm pretty dumb, particularly since I've spent a fair chunk of my professional life in high speed electronics, including developing and measuring sub-picosecond pulsed lasers.

And if you read my mail you'll see I was concerned about the accuracy of the sweep times of my 475.

Just out of curiosity, are you on the Tekscopes mailing list?

[Skywave]

I read your posts: I didn't see any 'mail' as such.

My post was not intended to be regarded as a 'tutorial': simply my attempt to justify my remarks.

I (obviously) have no knowledge of your professional life.

No, I do not think that you are, quote "pretty dumb", unquote. You've possibly made a measurement error: things like that happen to all of us, sooner or later.

The 'accuracy of sweep times' is not what my post was about: my post was to do with bandwidth of the vertical amplifier section in a Tek. 475 'scope.

I hope that all of that removes any mis-understandings between us.

Finally, no, I am not on that list to which you refer.

Al.

[Skywave]

Originally Posted by MrBungle

The 475 I had for a few weeks for repair measured up at about 245MHz of bandwidth (based on rise time from an avalanche pulse generator).

My post #12 applies to that, q.v.

Al.

[Philips210]

Hi.

I have a Tektronix 465 purchased in 2011 from the local junk shop for £10 but as yet I haven't been able to look at it. It's in reasonable cosmetic condition and I look forward to the challenge when I can find the time.

Regards
Symon.

[Craig Sawyers]

Originally Posted by Skywave

The 'accuracy of sweep times' is not what my post was about: my post was to do with bandwidth of the vertical amplifier section in a Tek. 475 'scope.

Checking the 10x magnified 10ns/div sweep time of my 475 - which should be 1ns per division, suggests is is closer to 2ns per division. Which is what I suggested might be the case in my original post

Running the test with a levelled sine wave suggests that the 3dB point is around 230MHz.

So I clearly need to do a laying on of hands on the sweep circuit of my trusty 475.

[ajgriff]

A word of caution for anyone reading this thread regarding over-tightening the set screws associated with the vertical attenuator boards on these scopes (465, 465B, 475, 485 etc). This applies to the boards themselves and the covers. Tek service engineers were very aware that over-tightening these screws would cause physical distortion and consequent unreliability in the switches and attenuator module connections. Thus the 'finger and thumb with a light grip' rule should be applied when tightening.

I speak from bitter experience!

Alan

[MrBungle]

Good advice. I only tightened them up myself when they had nearly entirely unscrewed themselves

[Skywave]

Bandwidth of 'scopes, measurement of.
I stand to be corrected / enlightened on this, but what follows is my understanding of this topic.

'Bandwidth' - in the sense of electronic equipment that uses analogue amplifiers and attenuators - is essential an analogue metric. Therefore, an analogue measuring technique is the only reliable method of accurately determining that bandwidth.
That statement is subject to the accuracy and resolution of the test equipment used plus how the various extra items of equipment (if necessary) are chosen, configured and used to make that assessment.

I will add one rider: the 'bandwidth' is -3 dB of the mid-band response. However, in typical use, it is often the case where the -1 dB (or less) freq. occurs that limits the usefulness of an item of measuring equipment.

Al.