Test Equipment Anonymous (TEA) : Discussion and Group Therapy Thread

[AVGresponding]

There was a lot of experimentation in the 60s and early 70s.

While working for Plessey, my brother gave me lots of hookup wire from West Drayton air traffic control centre, and later gave me a 19" rack insert full of 1" hollow metal cubes. Inside each cube there was four of these surrounding a central incandescent bulb.

IMG_9662.JPG

Guess what they are and what they were used for. (Not a chopper amp, substrate is ceramic)

Signal compressor/expander?

[Zenith]

The square thing looks like an LDR, so with the lamp some sort of photo-coupler, possibly for amplitude limitation. A similar thing was used as one of the various sorts of feedback methods used in ultra-low distortion audio oscillators, when they were looking for something better than a lamp or special self-heating thermistor. In that case they were a LED/LDR couple. You could make them up by gluing a LED to an LDR and making it lightproof with heatshrink or similar. My AWA G232 has what looks like a factory made one.

[tggzzz]

LDRs, yes, otherwise nice ideas but...

These were packed in tight, with little else on the PCB. At least 40, maybe 64 of them.

I don't think these were ever deployed en masse. At most a pilot installation.

EDIT: there were four LDRs surrounding each lamp, not the one necessary for AGC or companding. I'm not sure why there were four; maybe just a leftover from the traditional mechanisms used for the same purpose.

[Zenith]

Maybe some sort of relay system for a system of lights, maybe runway lights. Redundancy would be expected in a safety critical system. If so, it isn't obvious why they didn't just use relays because LDRs always have some resistance. Incandescent lamps have a limited life of a few hundred hours, depending on how they are run.

I suppose it could be part of some fail-to-safe alarm system.

[tggzzz]

Much closer

Mechanical relays aren't exactly wonderfully reliable. Coto relays in voltmeters do have to be replaced.

Incandescent lights can be very surprisingly reliable, particularly if inrush currents and and voltages are kept low.

[Zenith]

Mechanical relays were used in telephone exchanges with an unplanned down time of a couple of hours per decade. I've also seen them used in telemetry outstations. They are usually specified with the minimum number of operations they are expected to last, which can be a very high number.

DMMs may be an unfortunate example. They can develop faults which cause relays to chatter; oodles of operations of a sort they weren't designed for. They tend to be left on for long periods, so the chattering can continue overnight or even over a weekend. 30 to 40 year old TE has often been kept in poor conditions, such as a damp garage. It often has battery packs which have leaked and spread a miasma which has caused obvious corrosion.

Anyway, are you going to tell us what these curious devices were used for, or keep us guessing?

[EC8010]

These valves were never used in audio as I recall. There were probably problems with microphony and hum pickup. Valves such as EF86, designed for audio, had lot of work put in with internal screens, anti-microphonic construction and hum cancelling heaters...

...There was an HP3400B with JFET and IC chopper from the factory, I believe. I've never seen one.

There were a few interesting valves introduced in the last years of the valve era. A lot were for the TV industry, but there were a few very high performance designs, E810F and EC8010 of course. Then there was ECLL800, a triode presumably intended as a phase splitter, and two output pentodes all in a B9A envelope. Just the job for a very low power push-pull audio amplifier. I think they must have been trying desperately to compete against transistors. I have one somewhere.

You have to remember that audio in the 1960s was already so expensive that E88CC was far too costly to be used. And yes, you'd need DC heaters, which were a problem at the time. The internal screens in EF86 were actually guards to reduce grid current and allow the valve to be used as a (pretty poor) electrometer. But yes, the EF86 anti-microphonic construction and helical heater was definitely aimed at audio.

Despite having some E810F and (of course) EC8010, I haven't seen ancient circuits using them. The ECLL800 is truly dreadful. I found a Practical Wireless circuit using one to extract 5W (if memory serves) at appalling distortion. The operation of the phase splitter was appalling, yet the article was upbeat.

[Zenith]

You have to remember that audio in the 1960s was already so expensive that E88CC was far too costly to be used. And yes, you'd need DC heaters, which were a problem at the time. The internal screens in EF86 were actually guards to reduce grid current and allow the valve to be used as a (pretty poor) electrometer. But yes, the EF86 anti-microphonic construction and helical heater was definitely aimed at audio.

Despite having some E810F and (of course) EC8010, I haven't seen ancient circuits using them. The ECLL800 is truly dreadful. I found a Practical Wireless circuit using one to extract 5W (if memory serves) at appalling distortion. The operation of the phase splitter was appalling, yet the article was upbeat.

Special quality valves were often, but not always, enhanced versions of common valves. A lot were ruggedised variants and could tolerate levels of shock and vibe the commercial design couldn't. They were made on different production lines, used superior materials and better vacuum pumps were used. They were much more expensive than the base design. There were some applications such as military ones, where the extra expense was justified. There'd be no advantage at all in using them in say, a TV set.

ECC88 was a high mA/V double triode and I'd hazard was not much different in price to similar double triodes. I believe ECC189 was a vari-mu version and was used in some TVs. ECC88 was not used in audio because there were lots of other well established audio valves. It was a very popular choice in valve scopes in the 60s.

There was always a market for high quality audio, if not a mass market. Leak started by building amplifiers for cinemas and theatres before WWII. EF36 was originally intended as an RF pentode, EF37 was an anti-microphonic version better suited for audio,and EF37A was EF37 with a hum reducing heater. EF37A was much respected even after B9A valves came on the market. EF86 was developed with the performance of the EF37A in mind. EF40 came out before the EF86.

Brimar developed their own low-noise audio pentodes, 6BR7 and the misconceived 6BS7, which was the same but the control grid was brought out as a top cap. Brimar suggested that the 6BS7 was suitable for electrometer applications. No doubt GEC, who produced a lot of slightly different valves of their own, and mainly only used in their own products, also had a bash.

I don't know what the story was stateside. My RCA data book has loads of similar small pentodes.

Someone gave me a 60s VHF stereo receiver, which had been thoroughly trashed in transit and was beyond hope. That used ECLL800s. It's the only thing I've seen that did use them. It looks a lot like trying to get a quart into a pint pot. It was never popular.

I've got an E810F, which I bought for next to nothing at a swapmeet, because I'd heard of them and they have a phenomenally high mA/V. I really bought it out of curiosity. I've never come across anything that used them. They have a CV number, 5809 and a JAN number 7788 so there must have been military gear which used them. That does not cast light on what they were actually used for.

[tggzzz]

Anyway, are you going to tell us what these curious devices were used for, or keep us guessing?

AIUI, they were part of the switching fabric for speech signals in telephone exchanges. Thus they were a replacement for electro-mechanical relays of one sort (Strowager) or another (PO3000). I don't understand how they used four LDRs around a single bulb; I don't remember the LDRs being wired in parallel.

I'm not aware that any exchanges every used them.

I'll see if I can find out more.

[Zenith]

A telephone switching matrix avoiding electromechanical parts. That makes sense. A lot of work was done on automatic dialing over the years.

Plessey were very much involved in it in the 60s and 70s.

https://www.communicationsmuseum.org.uk ... /7.phphtml

It looks as if BT didn't want to swap out Strowger equipment until a reliable non-electromechanical solution was available, but that took a long time to come about. As you said, these Plessey boards were probably a pilot installation, which didn't prove entirely satisfactory and was forgotten.

[EC8010]

There was always a market for high quality audio, if not a mass market. Leak started by building amplifiers for cinemas and theatres before WWII.

Agreed, there was a consumer market, but it was poorly served. No consumer could afford to run tape at 15ips, so that left vinyl. Amplification of low-level signals was pretty crude; generally feedback and equalisation around an EF86 or ECC83. And the reason that was deemed adequate is that the signals that came off vinyl were poor. Oddly, that wasn't because cartridges were poor (Deccas and Ortofon moving coils were available), but because the turntables and arms were poor. Most arms had bearings that rattled, wibbly-wobbly joints, flimsy bits, and mass in the wrong place. Most turntables rattled as well rumbling. Garrard 301s and 401s were capable of low rumble but were typically put on flimsy light boards (BBC) or resonant soundboxes (SME plinth). A 301 or 401 needs serious mass (20kg or more) to soak up the vibration from its motor. Oddly, one decent arm was the Gray; a broadcast behemoth that (being a unipivot) had bearings that didn't rattle. The significance of arms rattling is that vinyl clicks and bangs were exacerbated and the RIAA stages of the day had very poor ultrasonic overload. All the ingredients were available for decent vinyl reproduction, but they were never used properly; the electronics designers really didn't think through what sort of a signal they were dealing with and the mechanical "designers" hadn''t a clue. You don't actually need fancy valves to make a far superior RIAA stage to the standard 1960s EF86 or ECC83 feedback stage, but using the ECC88 allows reasonably low noise (by modern standards) easier.

I was hoping someone might come up with an example of the use of an E810F. And another one I've never seen a use for is E55L. I have some of both.

Strowger exchanges were very reliable and uniselectors were an elegant solution. They were astonishingly noisy in operation.

[Zenith]

I was hoping someone might come up with an example of the use of an E810F. And another one I've never seen a use for is E55L. I have some of both.

It was used as the output tube in the vertical power amplifier of the 581A/585A. Except they called it the 7788. I thought everyone knew that .

https://w140.com/tekwiki/wiki/7788

If you look further down the page, it was also used in several other bits of Tek equipment and a Telequipment scope. In the 60s Tek bought out Telequipment because they wanted to enter the educational market, but they couldn't bring themselves to cut the corners necessary. Telequipment never had the slightest hesitation when it came to cutting corners.

E55L/CV8508/8233 was also used in Tek scopes, or rather some plugins for 500 series scopes.

https://w140.com/tekwiki/wiki/8233

I thought search with Google for E810F. Loads of links, but not much by way of applications. Then I thought, who could possibly justify using what must have been a ludicrously expensive valve like this? Tek! In the early 60s their scopes must have cost as much as a modest house. A Google search on E810F and Tektronix produce the link. HP probably used it

Same with E55L.

I'd guess a lot of valves like this were genuine OEM efforts, codesign, done with a few large customers in mind, such as the BBC or Tek, and then offered to the rest of the world. They had CV and JAN numbers, so presumably the military bought enough Tek units that they could insist on having the valves named their way, or there were other suppliers who used the valve, for radar, sonar, or whatever.

[tggzzz]

Then I thought, who could possibly justify using what must have been a ludicrously expensive valve like this? Tek! In the early 60s their scopes must have cost as much as a modest house.

Other rules of thumb...

In the 90s, the computer you wanted cost £1500.

In the 80s, a reasonable spectrum analyser cost them same as a small house.

In the 70s, the scope you used cost a years salary.

Now, how much would household insurance pay out for a 1980s 21Ghz spectrum analyser?

[vk6zgo]

I was hoping someone might come up with an example of the use of an E810F. And another one I've never seen a use for is E55L. I have some of both.

It was used as the output tube in the vertical power amplifier of the 581A/585A. Except they called it the 7788. I thought everyone knew that .

https://w140.com/tekwiki/wiki/7788

If you look further down the page, it was also used in several other bits of Tek equipment and a Telequipment scope. In the 60s Tek bought out Telequipment because they wanted to enter the educational market, but they couldn't bring themselves to cut the corners necessary. Telequipment never had the slightest hesitation when it came to cutting corners.

E55L/CV8508/8233 was also used in Tek scopes, or rather some plugins for 500 series scopes.

https://w140.com/tekwiki/wiki/8233

I thought search with Google for E810F. Loads of links, but not much by way of applications. Then I thought, who could possibly justify using what must have been a ludicrously expensive valve like this? Tek! In the early 60s their scopes must have cost as much as a modest house. A Google search on E810F and Tektronix produce the link. HP probably used it

Same with E55L.

I'd guess a lot of valves like this were genuine OEM efforts, codesign, done with a few large customers in mind, such as the BBC or Tek, and then offered to the rest of the world. They had CV and JAN numbers, so presumably the military bought enough Tek units that they could insist on having the valves named their way, or there were other suppliers who used the valve, for radar, sonar, or whatever.

Macaroni used most of these valves in their TV transmitters & ancillary equipment, so working with such things made us treat them as "common" types.

[EC8010]

Thanks for that. Subconscious had been mulling it over and thinking that E810F and E55L must have been the last flowerings of thermionic technology, designed in the hope that they would be needed, but never really used, hence them turning up now and again.

Good points about the cost of bleeding edge electronics. In about 1986 I saw a portable "C" format 1" broadcast quality videotape recorder. An Ampex VPR2 1" format studio machine was about the size of a (very) large fruit machine, costing > £50k, yet the beautiful Nagra VPR5 was tiny (by comparison). I think it only had 8" spools, and was probably 5" thick in total, but it was tiny. I asked how much it cost; more than twice what I had just paid for my first house. But it was a thing of rare beauty.

Thanks for the Marconi transmitter tip.

[vk6zgo]

Then I thought, who could possibly justify using what must have been a ludicrously expensive valve like this? Tek! In the early 60s their scopes must have cost as much as a modest house.

Other rules of thumb...

In the 90s, the computer you wanted cost £1500.

In the 80s, a reasonable spectrum analyser cost them same as a small house.

In the 70s, the scope you used cost a years salary.

Now, how much would household insurance pay out for a 1980s 21Ghz spectrum analyser?

Those of us who used such things which were owned by an employer were spoilt rotten.
If you had to buy instruments "out of your own pocket" in 1960s/70s, the pickings were few.

Having to drop back to a 10MHz single channel BWD, Telequipment, or even a Philips really hurt.
At least the BWD had a nice big display, unfortunately coupled with triggering problems.

[tggzzz]

Then I thought, who could possibly justify using what must have been a ludicrously expensive valve like this? Tek! In the early 60s their scopes must have cost as much as a modest house.

Other rules of thumb...

In the 90s, the computer you wanted cost £1500.

In the 80s, a reasonable spectrum analyser cost them same as a small house.

In the 70s, the scope you used cost a years salary.

Now, how much would household insurance pay out for a 1980s 21Ghz spectrum analyser?

Those of us who used such things which were owned by an employer were spoilt rotten.
If you had to buy instruments "out of your own pocket" in 1960s/70s, the pickings were few.

Having to drop back to a 10MHz single channel BWD, Telequipment, or even a Philips really hurt.
At least the BWD had a nice big display, unfortunately coupled with triggering problems.

Oh yes indeed.

Home scopes were never even a consideration for me; I always used the ones at home or work.

Spectrum analysers? Didn't even have one at work!

Computer? Yes the £1500 was for a home PC with, say, Win3.11. At work it was PDP11, Sun or HP workstations. In the mid 80s I did do DTP layout for a club magazine on a Mac - sneaking into the University of Cambridge computer lab late at night.

My home TE consisted of stuff I could make myself from scraps plus a Russian analogue multimeter. Had the major advantage of making me think how to do more with less.

It took me a long time to realise I could now afford good used TE, at which point I went overboard.

[EC8010]

Hmmm. I've had mixed experiences with second-hand kit. I used a second-hand Marconi TF2700 LCR bridge for twenty years before passing it on to a friend. Likewise an Advance 10MHz oscilloscope. But a Tek 485 costing £800 in 1998 only lasted two years before its EHT died. Just before it died, I bought a Tek TDS3032 that I still use. Second-hand kit from a dealer generally has a problem; that's why the original owners released it. No real engineer ever releases test equipment.

[tggzzz]

Hmmm. I've had mixed experiences with second-hand kit. I used a second-hand Marconi TF2700 LCR bridge for twenty years before passing it on to a friend. Likewise an Advance 10MHz oscilloscope. But a Tek 485 costing £800 in 1998 only lasted two years before its EHT died. Just before it died, I bought a Tek TDS3032 that I still use. Second-hand kit from a dealer generally has a problem; that's why the original owners released it. No real engineer ever releases test equipment.

It would be rare that a professional engineer used second-hand kit for professional purposes. If nothing else, calibration can be a lockout.

Using something at home, especially for a hobby, is an entirely different kettle of fish. Secondhand and (specialised) car-boot sale equipment enables me to do things I otherwise couldn't afford.

Company bankruptcies and moving divisions overseas are prime examples where the equipment is probably good - but the prices are such that I have to consider whether I can justify a purchase. Warehouse clearouts (often MoD) sometimes have gems. My voltage reference is a good example of the latter.

Problems can be impossible or trivial to repair.

There's a reason we've programmed a macro into our keyboards, "check PSU voltage/ripple and replace the electrolytics". And there's a reason "parts mule" exist

[Zenith]

Dealers like Stewart of Reading sell with a month's guarantee, and if they sell something as working, it works. I bought a Tek 475 which I used regularly for ten years. In that time a reservoir capacitor died and a small signal transistor expired. It still works now. It was probably 30 years old when I bought it. The other expensive TE I bought was an HP8640A. It was a pleasure to use for about 20 years, until it began to suffer from its plastic gears breaking up, which they all do eventually. I replaced it with a Marconi 2019, again from S of R, about 5 years back. That's been fine, apart from the OCXO reference being no longer up to its original spec. I have plans to replace it with an Aliexpress used OCXO, which are excellent.

All this TE had time limits more or less vaguely in mind. It was certainly expected to outlast the guarantee easily. There'd come a time when it was dropped from the price list. At some point, support contracts would no longer be offered. Original spares would eventually run out.

TE will be sold by the original owner for all sorts of reasons, and can have had very different use. It may have been rarely switched on, it may have been never switched off. Also big organisations have inflexible department budgets. Very often they buy new stuff they don't really need, to replace things that are still useful, so that the budget is spent. Re-organisations take place and companies close, so TE ends up orphaned and a general embarrassment to be disposed of, either by auction or straight to a dealer who will buy a job lot.

[tggzzz]

I can never convince myself what Stewart of Reading actually has in stock, nor what the price might be.

"For any equipment listed without a price, please enquire, as prices are currently under review" => I can't be bothered.

His "Best viewed in IE6" type website is also a severe negative, e.g. his special offer
Pendulum CNT90 6 1/2 Digit DMM True RMS IEEE £65
would be a bargain, but spot the error!

[Zenith]

S of R used to be a thriving business. The last time I spoke to him I got the impression it was more or less a retirement activity. He was rueful about the fact that the days had gone where he could place ads in the electronics mags, WW etc and the world was a straightforward place. This internet stuff is a bit much to keep up with. He does seem to have a good idea what he's talking about. I find it irritating to have loads of things listed with no prices and having to phone. Furthermore, the lists aren't completely up to date. For various reasons, the used TE dealer scene isn't what it was from the 70s to the early 2000s. There aren't so many proper used TE dealers around these days.

The items he likes to sell are in the £1,000 range, so fairly new and less likely to be troublesome, but he has a large amount of 70s, 80s, 90s classic gear, which he's doubtful about but will sell, if he can sort a good one out. He does occasionally have £10,000 plus items, but he's uncomfortable having expensive stuff like that around. He does have a Special Offers page on his website, which looks like the hard copy ads, and I assume this is items he has in stock with prices. Presumably, even in the old days, he could only list relatively few things and was happy for people to phone and ask what he had in stock.

The last thing I bought from there was a Marconi 2019. It turned out he had a few 2018 and 2019s. He sorted out the best and swapped a dodgy display, then burned it in over a weekend. When it was delivered, very well packed, it didn't work. So I phoned and told him, to pave the way for returning it. Then I opened it, reseated the boards and it was fine. It had been shaken up in transit. I phoned him and told him it had been fixed and had a pleasant chat about TE. His prices are generally comparable with ebay, with more certainty that whatever it is will work.

His pdf version of his special offers lists a Pendulum CNT90 Timer Counter Analyser 20Ghz £750. I'm sure the odd error and inconsistency creeps in when he compiles his lists. Ah! There are two versions of Special Offers, the pdf version where the Pendulum CNT 90 appears to have been listed correctly, and the html version, where it's been mixed up with a Solartron 7150 and the Pendulum labelled Pansonic.

If you were particularly in need of a 485 parts mule or two, it might be worth giving him a bell.

[tggzzz]

His pdf version of his special offers lists a Pendulum CNT90 Timer Counter Analyser 20Ghz £750. I'm sure the odd error and inconsistency creeps in when he compiles his lists. Ah! There are two versions of Special Offers, the pdf version where the Pendulum CNT 90 appears to have been listed correctly, and the html version, where it's been mixed up with a Solartron 7150 and the Pendulum labelled Pansonic.

HTML version looks fine in Chromium, leading to my IE6 jibe.

[Zenith]

I'm looking at the HTML version in FireFox and the bottom of it is garbled. eg

Solartron 7150 PSU 0-35V 0-2A 2 meters £30
Plus PSU 0-30V 0-2A digital £50
Solartron 7075 Function Generator 0.002-2MHZ TTL etc Kenwood £65

When constructing web pages for something important, it's as well to review them in all major browsers.

I did mention that he found this new-fangled interweb thing frustrating.

[tggzzz]

It is easy if you use HTML, and let the viewing device decide ow to show the content.

It is difficult if you use CSS and/or multiple layers of frameworks