Museum of failure.

[ColinTheAmpMan1]

Originally Posted by G6Tanuki

Another failure: Phonecards. They enjoyed a brief burst of popularity in the late-1980s through to the mid-1990s but thereafter faded into obscurity and irrelevance as phone-booths were obsoleted by ubiquitous and cheap mobile-phones.

These days there's still a niche-interest in collecting phonecards, In times past rare ones changed hands for truly unbelievable prices but they were a bad long-term investment. http://www.telephonecardcollector.co...rent-value.htm

So how much might this item be worth? Can I consider buying the Bentley Continental I've always wanted? I was given this ages ago and never used it. I think it still has units on it, but it is cracked in two places.
Colin.

[Herald1360]

Somewhat less than a large, tatty, 78 only radiogram with no triodes in it. There's nothing useful about it except perhaps emergency use as a frost scraper, or folded in two to stop that pub table from wobbling if there's no beer mat available.

[AC/HL]

I have a few Mercury phone cards. As with most things small enough to house, there is a market. It took off, but seemed to collapse around the time of the financial crisis. Yours looks quite early, so may have value, but the really valuable ones were the manufacturers trial ones, Landis and Gyr. Unused is best, but how do you know if you can't use it?
http://www.telephonecardcollector.co...rent-value.htm

[Refugee]

I have got a couple of unused phone cards that are still sealed in wrapping.
I think something in the phone strikes out the units as they are used up.

And don't hot laminate them!

[Refugee]

They are sealed in there original wrapping they were shipped in.

[Welsh Anorak]

Phonecards did serve a purpose, just became obsolete rather quickly. My field engineer had one and a pager (remember those?) so he could call the workshop from a stingy customer's house if a new job came in.
There is a kiosk across the road, but I fear its days are numbered. It's the new glass type, so no tears will be shed.
Glyn

And don't hot laminate them!

Lots of posts before mine, I was talking about thermal prints, ultrasound scans of babies in the womb are one example.

[G6Tanuki]

What about "Unijunction" transistors? They could be used in various trigger-circuits and frequently appeared in oscillator projects in Practical Wireless, R&EW, Everyday Electronics etc.

2N2646 ? With one of these, a couple of resistors/capacitors and a loudspeaker you could make a nasty-sounding Morse-practice oscillator [the note sounded like a damaged Stylophone]. I even remember seeing one used as an outboard quench-oscillator for a FM-band superregenerative receiver.

I never came across them used in any commercial/professional gear, which must say something....

[TonyDuell]

I've certainly seen unijuction transistors in commercial equipment. Most recently was a Chinese analogue multimeter I got at the last Dulwich museum sale which has inductance and capacitance ranges (the former being rather uncommon on an analogue instrument).

The basic idea for both of those functions was an oscillator followed by a monostable followed by an averaging circuit, so the meter displayed the duty cycle of the monostable output. For inductance the monostable was fixed (set by the range switch)m the oscillator a bipolar transistor colpitts circuit using the inductor under test. For capacitance, the capacitor under test was used in the monostable circuit, the oscillator was a unijunction transistor circuit (frequency set by the range switch).

I'm sure I've seen them elsewhere n better known brands, but I will have to dig through piles of diagrams to find them...

[emeritus]

In the 1990's I remember stories in the papers about lawyers going to court and finding that their faxed documents had faded to nothing. The cause was bleaching caused by the vapours given off by the plastic wallets they had been kept in. We were using a thermal fax at GEC at the time, and when I checked our files, found that our faxes were also becoming unreadable. We had to photocopy them and binned the plastic wallets in favour of paper/card ones, and got a plain paper fax machine when they became available.

I think I still have an unopened roll of 8 1/2" thermal fax paper somewhere that I had brought home for the kids to draw on that never got used.

[McMurdo]

Unijunctions are/were used in industrial thyristor drives for generating gated strings of firing pulses to hard-fire the thyristors driving inductive loads. I still have to use the 2n2646/2647 occsionally though they're getting dear.

[G6Tanuki]

Thermal-paper faxes could be rendered illegible merely by being left on a windowsill over a hot summer weekend.

In the 1980s I was responsible for supporting a number of Tektronix 40xx-series "Direct View Storage Tube" graphics-displays

https://en.wikipedia.org/wiki/Tektronix_4010

strange devices that used a conventional X-Y-deflected electron-beam to draw the vector-graphics on a relatively long-peristence phosphor along with a 'flood' cathode to provide electrons to keep the display visible once the drawing-beam had moved on.
[there was a facility to refresh the screen when the originally-drawn image had faded, or if you wanted to partially-erase areas of the already-written screen: this feature gave a disturbing plum-coloured background glow on the screen in the rewritten/erased areas].

There was a hard-copy unit for these displays - it used silver-oxide paper which was fed past a "single-line" CRT on which the screen-image was rescanned and reproduced a line at a time - so essentially you had a slow-scan video system with the line-scan being electronic and the frame-scan being mechanical!

The silver-oxide paper, alas, would over time degrade to a uniform level of greyness - as a few of our scientists discovered when they went back a few years later to look at the "screen-dumps" they'd included in their theses.

These days you're only likely to come across "TEK40xx" in emulation-form (and references to it in termcap/terminfo entries on historic Unix systems)

[russell_w_b]

Originally Posted by G6Tanuki

I never came across them used in any commercial/professional gear, which must say something....

A lot of early electric fencer units used unijunction transistors for triggering the pulse before the HV side. Prior to this they used a neon lamp.

[emeritus]

The paper referred to in #293 sounds like the stuff that was used in a multi-channel UV chart recorder that we were using at Plessey in the early 1970's. It was explicitly stated not to be permanent, and the unused rolls had to be kept in a fridge. I volunteered to investigate getting good-quality permanent copies that we could use in the report that I was preparing. We had a number of different makes of photocopier scattered around the site at the time, all with different colour sensitivities, but none of them were any good. In the end I took some sample traces to the print room and got them to copy them onto the 35mm microfilm that Plessey was using to make archive copies of its engineering drawings (unperforated, for mounting in apertured 80 column computer punch cards), as I knew from my hobby of photography that the type of film used was highly UV-sensitive. This worked a treat, the microfilm negatives being sharp, contrasty, and yielding a far better resolution than the original paper trace, and capable of producing good quality permanent prints of any size. One of the things we were using the recorder for, was to compare the analogue input and staircase output of the integrated circuit A-D convertors that we (not me personally!) had designed for use in our project. Our group leader had an A1-sized blow-up made of triangle-wave input and output traces showing the highly uniform step sized output of our design, and hung it in his room behind his desk to demonstrate our expertise to visitors.

[Andrew2]

Didn't the Philips G8 use a unijunction in the frame osc?

[turretslug]

I'd been curious about the unijunction transistor, too- I almost wondered if someone like RCA had accidentally made a few million through a process lapse while making BJTs- "ahem, there's a bonus in this if we can persuade folk to buy them, get busy with the breadboarding...."

To be fair, there seemed to be a fair bit of inventiveness and creativity going on early in the history of semiconductors, some ideas flourished, others vanished fairly early on.

[Refugee]

I read some time in the 1970s that occasionally you could find a BJT that would work as a UJT in those bags of unmarked devices.
I found one in a TO5 can but that was all.
Perhaps that is what sometimes makes transistor amplifiers burst into oscillation for no good reason on the odd occasion.

[suebutcher]

About the modern thermal receipts, if they're faded you can heat them gently until they start to go grey, and sometimes this enables the print to be read in negative.

[TonyDuell]

Originally Posted by G6Tanuki

These days you're only likely to come across "TEK40xx" in emulation-form (and references to it in termcap/terminfo entries on historic Unix systems)

That may be true in general, but not on a vintage technology list. [Looks at my Tek 4006 storage tube display and 4027 colour (raster scan) graphics terminal which has the hard copy output connector option fitted].

As regards the Teketronix 'copiers' (these photographic printers that fade), I am told by people who have them that there are no rolls of useable paper left anywhere.

Another long-forgotten printer technology (I am not sure it was a failure, certainly I have seen several of the units in use years ago) was the electrostatic matrix printer of the Versatec type (V80 is one well-known model). These work by passing specially coated paper between 2 sets of electrodes and building up a charge image on the paper a line at a time. Liquid toner is then passed over the paper and is attracted to the charge image. The liquid evaporates leaving the toner behind.

The quality was quite good for 35 years ago (200 dpi or so) but the liquid toner was messy, the pump blocked (and unblocking it by the suck-it-and-see method proved that toner tastes foul) and the evaporating (hydrocarbon-based) carrier liquid made the machine room smell like an airport.