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Old 22nd Jan 2022, 6:03 pm   #1
mole42uk
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Default Best 100MHz analogue oscilloscope?

I have several oscilloscopes, but my go-to is a Tektronix TAS250 which is a bit poorly but otherwise does what I need.

I'm thinking about replacing it, if I specify a used 100MHz analogue oscilloscope for a hobby workshop, which would not disappoint? Budget wise, I'm a Yorkshireman, so as cheap as possible, but I'll pay good money for the right thing!
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Old 22nd Jan 2022, 6:22 pm   #2
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Default Re: Best 100MHz analogue oscilloscope?

Hi!

If you're happy with an ordinary plain vanilla analogue one, why not get another 465 or 465B ?

Admittedly the internal access and repair is grotesque, but there's tons of spares and I'm sure other members'll be able to come up with spare bits!

(I appreciate it's a bit morbid to say so, but they do come up from time to time very cheaply, often when an amateur or hobbyist with one unfortunately passes on, these often go a lot cheaper than the silly overpriced offerings by T & M or commercial vendors! That's how I got many of my cheapie ones in my collection!)

Performance wise, the triggering on the 465/465B is excellent, they have a very bright, (altho' not the finest of traces as they use an expansion–mask CRT), most of the circuitry is well known, understood and reliable!

Items likely to need replacement are:–

a) Power Supply Electrolytics on Main Board A4, special little Adapter PCBs are now offered by various sellers to allow the fitting of standard 10 mm pitch PCB electrolytics without making a mess of the original PCB;

b) Attenuator leaf switches need cleaning, the procedure has been documented on here a number of places;

c) Overloading the inputs can damage the little plug–in DIL format attenuator modules, but these are used in a number of Tek 400 series and 7000 series scopes, I believe members can supply a few spares!

The 465B is the better of the two as this meets the 100 MHz bandwidth easily with a bit to spare, the earlier 465 doesn't always do so!

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Old 22nd Jan 2022, 7:02 pm   #3
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Default Re: Best 100MHz analogue oscilloscope?

Hi!

As a PS to the above, the available 465B pdf books have been incomplete for many years, but thanks to efforts by Member "Dickie" Richard and others on the "dxdevs" Repair Site, all the missing tables and missing circuit/layout diagrams 4, 6, 9 and 10 is now freely available online!

I recommend QService's 465B Manual CD – buy the one identified as "465B LOW and HIGH Serials", then you have both variants!

Unfortunately I found the quality of the Artek one, which I bought at Christmas, disappointing!

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Old 22nd Jan 2022, 7:34 pm   #4
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Default Re: Best 100MHz analogue oscilloscope?

I don’t think you can really go wrong with an analog scope from Tek or HP. However I have wasted countless hour keeping these things up and running as they are getting old now and parts failure are common. In my opinion scope are horrible things to work on and the 465 especially. You may already have one but I’m going to commit the ultimate sin and say just buy a new rigol or siglent. If you haven’t tried a modern scope you will love the measurement feature and the warranty. Let the roasting commence!
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Old 22nd Jan 2022, 8:16 pm   #5
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Default Re: Best 100MHz analogue oscilloscope?

Don't underestimate the HP 1740A

It has a few things going for it.

1) Internal access is a whole world easier than the Tek 465/465B

2) No HP scope has ever triggered on any waveform ever, just check the internet! Remind the seller of this and you can haggle him down to pennies.

3) No fan noise... no fan... importantly no need for a fan. Runs cool.

4) Switched 50 Ohm terminations on both channels.

5) Everyone I've had comfortably exceeds bandwidth spec.

6) ECL trigger logic, no tunnel diodes.

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Old 22nd Jan 2022, 9:37 pm   #6
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Default Re: Best 100MHz analogue oscilloscope?

Quote:
Originally Posted by ChristianFletcher View Post
I donít think you can really go wrong with an analog scope from Tek or HP. However I have wasted countless hour keeping these things up and running as they are getting old now and parts failure are common. In my opinion scope are horrible things to work on and the 465 especially. You may already have one but Iím going to commit the ultimate sin and say just buy a new rigol or siglent. If you havenít tried a modern scope you will love the measurement feature and the warranty. Let the roasting commence!
It all depends on whether you enjoy repairing old 'scopes. For some it's part of the hobby.

I've shifted my position over the years. I've owned Tec 465's (etc) and kept them working. At the time when digital 'scopes were pretty grim, they were definitely worth considering .... even with the diabolically bad internal layout and lack of serviceability ease.

However, now digital 'scopes have come on in leaps and bounds and decent performance has descented down from instruments costing many thousands to instruments more affordable to the hobbyist. Unless you enjoy fiddling with old scopes, I would at least take a look at affordable digital scopes.
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Old 23rd Jan 2022, 7:26 am   #7
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Default Re: Best 100MHz analogue oscilloscope?

If you really want an analogue scope, and I have much sympathy for you in that (I still turn to a good analogue scope before a digital one for debugging) how about the Tektronix 2445? The 24xx series are considered by many to be the pinnacle of portable analogue scope design. There are many models in the series, the 2445 having 150MHz bandwidth and the 2465 300MHz+. They have lots of useful features, the cursor measurements are good, and they're reliable. Stories abound on the Internet of people dealing with capacitor failures in their 2465Bs, but there's a simple solution to that: don't get a 2465B. The earlier 2465, for example, doesn't have failure-prone capacitors. The 2445 will be similar.

I keep a 2465 in the loft in our house in the UK to use when I'm here. I bought it in about 2004 from M&B Radio in Leeds and I've literally never had the covers off it. Last June I visited for the first time in 18 months because of the pandemic. Got the scope, switched on, no problem. This week I pulled it out again after another 6 month break - works perfectly, everything still accurate. Not bad for a 35-year-old scope. Of course, with equipment this old, anything could happen, but the fundamental design of the 2465 seems very solid.

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Old 23rd Jan 2022, 9:05 am   #8
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Default Re: Best 100MHz analogue oscilloscope?

You must have got lucky & got a Tek 2465 without RIFAs in the PSU or a Schaffner line filter, I think one of mine didn't have them.
Also the Sprague electrolytics (alu can with red seals) in the PSU like to leak corrosive electrolyte, maybe yours has a different brand fitted.

Anyone that does re-cap the PSU of a 2445/2465 series scope should note one of the manuals has an error, two capacitors are swapped on the diagram, if followed you end up with a low voltage capacitor fitted to a high voltage rail, with resulting smoke, this was covered in an eevblog video a few years ago where this happened.

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Old 23rd Jan 2022, 4:02 pm   #9
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Default Re: Best 100MHz analogue oscilloscope?

the Tek 2245A which is 100MHz and 4 channels is quite nice to use although 2 CHs are only really for logic levels.

I got a 2445B as a non worker, plugged it in and switched it on and was delighted with the bright display before the Rifas said no ( I know I should have checked first but there you go) I changed the Rifas but still have to fix the original fault. it's only got 200 hours run time on it ( ex mod) so it will be nice when it's done. frequency counter on CH1, cursors etc.

I got a 2232 which is rather nice for 100 quid. analogue 2CH but with basic ( these days) digital storage. drives like a 'real' scope. another bargain was a TAS485. 4CH 200MHz but menu driven. the only problem with all these scopes on a day to day basis is the fan noise...
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Old 23rd Jan 2022, 4:29 pm   #10
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Default Re: Best 100MHz analogue oscilloscope?

I second Radio Wranglers comments re the HP 1740A plus has a max sensitivity of 1 mV/div at 40mHz b/w, excellent triggering plus all the other bits. Upgraded from an HP 180 that but the dust.


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Old 23rd Jan 2022, 4:42 pm   #11
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Default Re: Best 100MHz analogue oscilloscope?

I have three Tek 24xx series scopes in various places. I think they've all got the infamous Rifa exploding capacitors in. They've all gone snap-crackle-pop at various points in the past and I've done precisely nothing about it, just left them. The dirty secret is that they continue to work just fine afterwards so, until one of the injured capacitors breaks down and starts tripping circuit breakers or I have some weird EMC conducted emissions problem from their power supplies, it's just not worth the trouble of fixing them. They've all been in that state for about 10 years, in frequent (professional) use.

Let the Rifas do the sweating, not you.

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Old 23rd Jan 2022, 6:06 pm   #12
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Default Re: Best 100MHz analogue oscilloscope?

it was one of the Rifas in the snubber networks that went on mine which blew the mains fuse, and burnt a 27 ohms resistor plus the board which was a bit annoying. quite a lot of disassembly required to get the board out so while I was there I changed all the Rifas plus the some of the electrolytics
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Old 23rd Jan 2022, 8:28 pm   #13
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Default Re: Best 100MHz analogue oscilloscope?

Thank god for Rifa capacitors they have secured me many cheap spares or repair test gear from eBay. Got to love an easy fix
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Old 23rd Jan 2022, 8:54 pm   #14
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Default Re: Best 100MHz analogue oscilloscope?

I like to say the best 100MHz scope is a 200MHz scope (or faster),
this means also the both probes. So your unit works at 100MHz not at the end of the street

Tek 475 will do that, or one of the old 7704 frames with 7A26

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Old 24th Jan 2022, 4:45 pm   #15
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Default Re: Best 100MHz analogue oscilloscope?

Philips made a lot of nice 'scopes.

The PM3267 has traditional knobs and buttons, but not the crispest CRT.

Later ones had the pushbutton+LCD interface, but really sharp CRTs.

Later still moved from brown to white cases, and there was a move to buttons+rotary encoders, with the on-screen text replacing the LCD. Some of these were badged Fluke. Some models were 4 channel, some went to 200MHz, and some were "CombiScopes". I have a PM3380A, which is a 2 channel, 100MHz analogue/digital unit, and love it. The worst thing I can find to complain about it is the slightly noisy fan.

I also have a PM3295, which is a 350MHz beast. There was a later A model that went to 400MHz. Obviously aimed at the Tek 2465 models. Personally, I prefer the Philips. It has a nicer user interface (buttons with status LEDs built in and little backlit LCD displays above the rotaries, so you don't have to rely on the on-screen text) and a much sharper CRT (21kV acceleration voltage!).

I have the use of many Tek 'scopes at work, including some quite posh ones, like the 2465B, but I genuinely prefer the Philips equivalents. I've never had a custom part fail in a Philips before, but we've had several Tek modules go bad over the years.

Philips use similar inline filters to Tek, so expect them to let go in the usual way. I wouldn't ignore one that's done its work though - I don't imagine the deposits left behind are very nice (happy for someone to set me straight on that - I wasn't great at chemistry!).

I've spent over a decade - on and off - trying to restore a HP1740A. Still not quite there. A donor machine helped a lot, but I keep running out of enthusiasm to finish it. The trouble is, once done, it will be bigger than my other 'scopes, and no more capable. I agree that it's much easier to work on than the Tek equivalent, and being fanless is an important benefit. In fact, that's why my "daily driver" is still - after 30+ years - a Telequipment DM63. If I need more bandwidth, I'll use the PM3295. If I need storage, I'll use the Rigol DS1054 (which is now 100MHz, though quite a bit more in practice if you measure it). But the added bandwidth comes with all sorts of complications if you want to use probes, as alluded to above...
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Old 24th Jan 2022, 5:12 pm   #16
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Default Re: Best 100MHz analogue oscilloscope?

I use the Tektronix 2465 which is a fantastic scope.
*BUT* it contains digital electronics (no signal processing though) and mine has now lost some bits from the ROMs so has to be started using the "override" to the error that is flagged, at which point I find a bit or two missing from the on-screen characters.

Before that I had Tektronix's amost 100MHz lightweight portable , the 585A
This was a great scope too and no problems fixing it. Nothing digital and all very spread out for easy access. But you had to be careful to use the correct funny solder and lifting gear helps.
The main snag was that in summer you risked problems from sweat dripping into things, but in winter it doubles as a fan-heater
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Old 24th Jan 2022, 7:40 pm   #17
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here is the 15th of Heerenveen
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Old 24th Jan 2022, 8:51 pm   #18
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Default Re: Best 100MHz analogue oscilloscope?

-No need for a fan heater in Martin's workshop..
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Old 24th Jan 2022, 9:33 pm   #19
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Default Re: Best 100MHz analogue oscilloscope?

Ah but if you opt for a separate fan heater and oscilloscope, you can turn the heater off in summer.

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Old 24th Jan 2022, 9:35 pm   #20
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Default Re: Best 100MHz analogue oscilloscope?

Nobody likes Hamegs?

We have a couple of Hameg 1505s at work, typical CRT / analogue Hamegs running at an untypical 150MHz (The rest of our Hamegs are run of the mill 20MHz models).
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