Tektronix 475

[Zenith]

This came from a swapmeet a couple of weeks back for a parts mule price. It has no missing or cracked knobs and had the document pouch and the front cover. There are no cracks in the timebase knob. The front cover makes the scope easier to store, keeps grot from accumulating on the front and prevents damage, and makes it far easier to remove the cover. They are usually missing. The calibration seals weren't broken, which is unusual, in fact I can't recall buying any used instrument before with the seals intact. This one was made in the Netherlands and the date codes on the electrolytic capacitors are from 1982, which puts it right at the end of the 475's production life.

It had a sticker saying, "Powers up. Buzzes. No beam".

I really meant to put it aside until various pressing but boring jobs have been done, but it's been raining and I couldn't resist having a look at it.

I took off the cover and eyeballed it for anything missing, burned, bodged or disconnected. I powered it up and there was a buzzing noise. Was the transformer overloaded by a short? It turned out to be the fan catching on the metalwork at the rear. The fan was shifted along the shaft a little way, (it's fixed with an Allen key). It's still a bit loud. Perhaps the motor bearings could do with lubricant.

All power supply lines showed massive ripple on a scope. They are all referenced to the +50V line. Likely candidates were the reservoir electrolytic capacitors on the 50V regulated line. I suppose it could have been a dry joint or the bridge rectifier but there appeared no sign of a dry joint and bridge rectifiers seldom fail.

I removed the two electrolytics which are 350µF and 1000µF cans, both 75V working. I tested them with a Peak LCR meter. The 350µF was about right, the 1000µF had a capacitance of 79pF. I didn't have any suitable replacements, so I codged up substitutes using two 150µF and two 470µF 200V caps, so that problem could be eliminated and the scope could be examined further. It's a horrible bodge and I'll have to add some proper capacitors to the order for Digikey.

DSCN3953.JPG

No problems on powering up the scope and mV of ripple on the supply lines. The +50V line was almost spot on and the other lines were as they should be.

The scope works and displays the calibration square wave. It looks as if the trace is affected by mains hum and it's a bit fuzzy. I know that 475s aren't noted for the sharpest traces. The delay sweep works. The +/- slope triggering doesn't do much.

DSCN3952.JPG

DSCN3951.JPG

It needs a thorough checking out and calibration with contacts cleaned or unmade and made. There may be other problems I didn't spot with a quick look over.

I've put it away with a note saying what was done. I'll deal with it properly later, when more important things are out of the way. Generally I'm pleased with it so far.

[tggzzz]

If the the cover is off, a bit of hum wouldn't surprise me.

[MED6753]

You will pick up noise and fuzz up the trace with the cover off. I speak from experience.

[Zenith]

Thanks both of you for that. Scopes will pick a lot more hum and noise with the cover off, but I've not seen it this bad before.

With the cover back on things improved a lot. it also helped to use a Tek probe rather than the Chinese one I usually reach for. I think the Chinese probe doesn't make a particularly good earth contact on these BNC sockets. I've never noticed problems with it before.

The trigger problem has disappeared.

The fuzziness has decreased a lot, and even further when the 20MHz filter is in, which indicates noise in the vertical preamps. Some of the rotary switches are a bit noisy. At a quick look, the calibration is pretty much right.

It needs that horrible capacitor bodge doing properly, contacts cleaned and the calibration procedure worked through and then it will be as good a 475 as you can expect to find. There may be other problems discovered along the way.

[mnementh]

*sniff-ity-snifffs the air*

What is that smell...?

mnem

[Zenith]

Naah! Tants were a miracle component around 1970. Small, low leakage and better at RF. They were overused, especially across supply lines, and the technology was immature. I've never noticed any particularly bad smell when I've seen them fail.

The for real, never forget it smell, comes from a dying selenium rectifier. The fact is the chemistry of selenium was held up for many years because the compounds were so unbelievably smelly. Tellurium was even worse.

One of the worst electrically related things I've come across, was from a failing vacuum cleaner motor. When I was 13 I strapped it to a box and powered it up. It struggled a bit and got hot. The fumes were incredibly unpleasant and produced tears.

[tggzzz]

The for real, never forget it smell, comes from a dying selenium rectifier. The fact is the chemistry of selenium was held up for many years because the compounds were so unbelievably smelly. Tellurium was even worse.

How about thioacetone? https://www.science.org/content/blog-po ... hioacetone

During early experiments, a stopper jumped from a bottle of residues, and, although replaced at once, resulted in an immediate complaint of nausea and sickness from colleagues working in a building two hundred yards away.
...
To convince them otherwise, they were dispersed with other observers around the laboratory, at distances up to a quarter of a mile, and one drop of either acetone gem-dithiol or the mother liquors from crude trithioacetone crystallisations were placed on a watch glass in a fume cupboard. The odour was detected downwind in seconds.
...
"So there you have it - just install a fireplace next to your hood (what every lab needs, for sure) and remember that, in a thioacetone situation, fogging the area with brown nitrogen oxide fumes will actually improve the air.



But he also mentions carbon diselenide https://www.science.org/content/blog-po ... diselenide

A colleague of mine had a copy of this paper in his files, and he treasured a footnote from the experimental section which related how the vapors had unfortunately escaped the laboratory and forced the evacuation of a nearby village.
...
and there's actually a commercial source for the disgusting stuff (which may be a first.) I'd like to see what they ship it in.

[bd139]

The 475's are noisy as hell fully opened up. It was a regret of one of the designers if I remember reading it correctly.

Still respectable scopes though!

[Zenith]

They are getting on a bit though. I've had one since 2009. It's failed twice. The first time was a reservoir cap, I think the same one as failed in this. The second time was a transistor in the trigger circuit which is under no particular stress but decided to depart this life. I had a couple of spares in an assorted bag of transistors I bought from Greenweld - does anyone remember them? On balance I like the fact that the transistors and some other parts in these things are socketed.

I never took to the fuzzy display. When I bought the one in 2009, it was the sharpest of three I saw running. I've run them with no covers on before and I was surprised how bad it made this one.

If you run one, you really need a parts mule because unobtainable things will fail or break. So I bought a parts mule, but it was so close to working it was a shame to use it for that and I fixed it. So I bought another part mule which is further from working but not hopeless. Then this, which looks pretty damned good so far and was easily fixed. With some TLC it might turn out to be the best of the lot. I need another couple of true parts mules - missing knobs, obviously damaged CRT, and a fiver a pop. That might end the process.

It's a slippery slope. Young people reading this, don't be tempted to mess with a Tek 475. Don't even try one behind the cycle sheds because all the cool guys are doing it.

I've yet to start on 475As and 485s.

[tggzzz]

Greenweld - does anyone remember them?

Oh yes.

BiPak anyone?

Still have many ~BC108 I got from that kind of place.

[bd139]

Do they actually work? Most of the stuff they sold were factory rejects.

I was actually in Bi-Pak territory the other day (Ware) on an amble with a potential new bd140. Definitely gone a bit more upmarket than it was!

[tggzzz]

They worked, but I never had equipment to measure various parameters.

RS 741s used to be in spec, but with a bimodal input offset voltage. Clearly TI etc had kept the better parts for themself.

The practice continues, of course. Think of Farnell's MultiComp brand.

[Zenith]

Looking at one of their ads from 1974, BI-PAK sold BC108 and other transistors "Brand new fully guaranteed devices" for 14p which is in the same range as other sellers. They also sold PAKS, some of which were tested and guaranteed and others not. The only BC108s in the PAK section of the ad were "25 silicon NPN transistors like BC108", untested and unmarked for 55p. "Satisfaction GUARANTEED in every Pak, or money back".

I'd guess they were fairly honest merchants and most of the stuff in the untested Paks was OK. For a lot of applications any small signal transistor with a Beta of 50 or more would do.

The transistors I got from Greenweld were 200 assorted ones for half-price in their sales. I recall that was £1.50. There were probably 30 or 40 different types. I've used a fair few and haven't had a bad one.

Another somewhat shady lot were Z&I Aero Services who sold valves. A lot were made in the USSR, or were remarked in some way. I have a Z&I box marked KTW61 with a valve inside marked KTW61, except it's obviously a 6K7G, which is a rough equivalent.

The Multicomp components I've used are capacitors and resistors. I've had no problems with them, but given an easy alternative, I'd rather not buy them.

[tggzzz]

Another somewhat shady lot were Z&I Aero Services who sold valves. A lot were made in the USSR, or were remarked in some way. I have a Z&I box marked KTW61 with a valve inside marked KTW61, except it's obviously a 6K7G, which is a rough equivalent.

I bought my Russian multimeter from them in November '75. It has a good hard case, and the only thing wrong with it is that the red scale has faded in 49 years.

The Russians captured the low-end functional market for several types of items in that era, because the stuff was cheap and solid. Anybody remember Zenit SLR cameras?

Their armed forces equipment was much the same. IIRC the Foxbat avionics were based on nuvistors.

[Zenith]

Z&I Aero Services sold a lot of Russian stuff, including TTL. I've got some Zaerix CV138 (EF91) made in USSR. CV was the UK military valve designation. When Western makers started to drop out of the valve business, by the end of the 60s, the military still had a lot of equipment that needed valves, such as the RA17 and R390A receivers, which were kept on because they could withstand EMP and hefty doses of RF from radars etc. I thought it was ironic that one of the ultimate cold war receivers (there were hundreds of them in GCHQ) was kept going, officially fitted with Russkie valves.

IIRC Z&I Aero Services eventually went under as a result of a passing off action.

I knew someone who had a Zenit camera. It worked very well, but didn't have TTL metering, and it was built like a tank and was heavy as lead. They were £40 when the cheapest Japanese SLR was £150. Praktica (East German) were a bit more refined and cost £50.

Then there were the Russian shotgun cartridges, Baikal Record brand. There was something of a craze for them in the 80s. They were very low pressure but very high velocity - 1450 fps. They were £2 for 25 when other brands were £3 or more. You could buy them for £40 a thousand.

They were "interesting". They always went off with a walloping bang. Sometimes there was a sheet of flame two feet long coming out of the barrel. Sometimes they produced a big cloud of smoke. Sometimes they produced a shower of confetti. Occasionally they'd do all four. A lot of clay shooting grounds refused to let them be used.

[Specmaster]

The Russians captured the low-end functional market for several types of items in that era, because the stuff was cheap and solid. Anybody remember Zenit SLR cameras?

Yes, I do, I had one for many years (it was a Dixons Prinz badged one, poorly done, a plastic badge stuck over the Zenit logo, but it did take some decent photos and built like a battleship, never ever let me down. It went after years when I decided to upgrade to a Canon SLR, then later onto Canon DSLRs, never looked since then.

[tggzzz]

The Russians captured the low-end functional market for several types of items in that era, because the stuff was cheap and solid. Anybody remember Zenit SLR cameras?

Yes, I do, I had one for many years (it was a Dixons Prinz badged one, poorly done, a plastic badge stuck over the Zenit logo, but it did take some decent photos and built like a battleship, never ever let me down. It went after years when I decided to upgrade to a Canon SLR, then later onto Canon DSLRs, never looked since then.

I continually looked at Zenits, but always had more urgent uses for my money. Eventually I got a Yashica SLR

That was, in turn, replaced by a Zeiss Ikon Contaflex, a Stereo Realist, and a Nimslo. I still have the latter two and the Yashica, but recently sold the Contaflex for a pleasing profit

Not sure how people take stereo pictures now; synchronising two electronic cameras seems like a recipe for frustration.

[bd139]

Was Praktica here (MTL5B). I have one in the cupboard

They sell stereo lenses now.

As for sync, most of the mid-high end DSLR and mirrorless cameras can sync with each other using various methods. All wireless on Nikon. You can even remote control them from SnapBridge on your phone. The master camera acts as a WiFi AP. Things have come a long way.

[vk6zgo]

They are getting on a bit though. I've had one since 2009. It's failed twice. The first time was a reservoir cap, I think the same one as failed in this. The second time was a transistor in the trigger circuit which is under no particular stress but decided to depart this life. I had a couple of spares in an assorted bag of transistors I bought from Greenweld - does anyone remember them? On balance I like the fact that the transistors and some other parts in these things are socketed.

I never took to the fuzzy display. When I bought the one in 2009, it was the sharpest of three I saw running. I've run them with no covers on before and I was surprised how bad it made this one.

If you run one, you really need a parts mule because unobtainable things will fail or break. So I bought a parts mule, but it was so close to working it was a shame to use it for that and I fixed it. So I bought another part mule which is further from working but not hopeless. Then this, which looks pretty damned good so far and was easily fixed. With some TLC it might turn out to be the best of the lot. I need another couple of true parts mules - missing knobs, obviously damaged CRT, and a fiver a pop. That might end the process.

It's a slippery slope. Young people reading this, don't be tempted to mess with a Tek 475. Don't even try one behind the cycle sheds because all the cool guys are doing it.

I've yet to start on 475As and 485s.

The first 7000 series Tektronix that my old work had was supplied with one of the plugin spaces empty & no dummy cover on the hole.
The display appeared to be very fuzzy compared to our 545B.
The problem was our Aust CH 2 TV transmitter with its vision carrier at 64.25 MHz, & once we got the dummy cover it was much less fuzzy.

[vk6zgo]

Another somewhat shady lot were Z&I Aero Services who sold valves. A lot were made in the USSR, or were remarked in some way. I have a Z&I box marked KTW61 with a valve inside marked KTW61, except it's obviously a 6K7G, which is a rough equivalent.

I bought my Russian multimeter from them in November '75. It has a good hard case, and the only thing wrong with it is that the red scale has faded in 49 years.

The Russians captured the low-end functional market for several types of items in that era, because the stuff was cheap and solid. Anybody remember Zenit SLR cameras?

Their armed forces equipment was much the same. IIRC the Foxbat avionics were based on nuvistors.

The Russki cameras never took off in Oz for some reason--there were a few on sale, but in the main, the market was Japanese all the way apart from a few expensive West European brands.
(There were always those few who were still dedicated to Kodak,but they were "the afflicted".)

I had a Minolta SRT101 which was a bit more costly than the other brands

When I went by sea to the UK in 1971, we stopped at Curacao on the way, which had a lot of shops selling watches & stuff and a couple with cameras.
I had a look at the SRT101s they had, & was surprised that they were more expensive than in Australia.
They were cheaper than in the USA, though, as there were Americans snapping them up like hot cakes.

The same applied in the UK, as I could have sold it for more than I paid for it, which was surprising, considering the size of the photographic community in that country.

[Zenith]

My impression was the Zenit cameras sold but they weren't wildly popular. Praktica sold better and were a better camera. Dixons, which was a large chain, sold them. Japanese cameras had most of the serious camera market. it was something of a status thing and in the 70s, Pentax and Olympus etc were heavily advertised in the Sunday newspaper magazines. There were western European cameras; Leica, Contax, Hasselblad, all at astronomic prices. By the mid 80s there were a lot of very good SLR brands around and prices came down.

In the late 70s a colleague went to visit his son in Oz and brought back a catalogue from an electrical goods store. Everything seemed much cheaper than in the UK. About 8 years ago some neighbours moved to Oz. She was Australian and couldn't stand the winters here. I saw them moving out and they were loading the washing machine and dish washer. I said it seemed odd to pay to ship that stuff to the other end of the globe. They said it was worth doing because those items were incredibly expensive in Oz. Maybe times have changed.

Minolta and few others dropped out of the camera business years back.

[AVGresponding]

iirc Minolta hoovered up (sorry, not sorry) a number of other camera brands (Konica, Yashica etc) and some of them may still be in operation, or the brand names sold to the Chinese, not sure...

[Zenith]

According to wikipedia Minolta merged with Konica in 2003 and dropped out of photography and photo-imaging in 2006/2007. The company still continues making office equipment, TE, medical imaging and optical devices. Seems like they made a smart move, getting out of market in which they'd done well, but which had changed and they hadn't managed the transition all that well.

A lot of those companies which were big in the day closed, or merged, or only continue as brand names. Bush Radio, which was a major producer of radios and TVs, became not much more than a brand used by the Rank empire, by about 1980. It still continues as a brand sold by Argos.

[25 CPS]

iirc Minolta hoovered up (sorry, not sorry) a number of other camera brands (Konica, Yashica etc) and some of them may still be in operation, or the brand names sold to the Chinese, not sure...

iirc Minolta hoovered up (sorry, not sorry) a number of other camera brands (Konica, Yashica etc) and some of them may still be in operation, or the brand names sold to the Chinese, not sure...

I could've sworn that Sony bought Minolta's camera line and that's how they entered the still photography market. I had a Minolta film scanner that I bought in the early 2000s shortly before Minolta got dissolved and that whole line of business got dropped.

[AVGresponding]