"Interesting" hour or so....

[Herald1360]

Just spent a while running a batch of NOS red and white spot transistors past my cheap multimeter box. They were part of a "storage drawers with assorted components" lot from RWB auction yesterday.

Out of 61 red spot types 47 were actually transistors with varying beta and leakage, only 14 were either totally dead or else seen as one or two diodes.

The white spots (rf types, allegedly) were awful, only 5 actual transistors, 4 of which had reversed makings or at least were labelled as such by the tester.

I wonder how frustrated hobbyists were back in the day trying to use these things with limited or no access to decent test equipment?

[G6Tanuki]

Equally, I wonder how many of them might have been adequately-serviceable transistors back in the late-50s/early-60s when they were first sold to impoverished constructors, but have suffered ageing-related issues over the subsequent half-century-or-more?

I recently had an issue with a "KW" SWR-meter that used a ceramic-envelope point contact diode; it must have worked back in the 50s when the thing was made, but it had gone open-circuit since.

"New Old Stock" parts are subject to ageing just as much as parts-in-service. Don't bother buying NOS AF11x/OC17x transistors, they're likely to be just as tin-whisker-plagued as the transistor you were intending to use them to replace!

[Herald1360]

If they'd been AF11x or OC17x or any other tin plated can type I'd be inclined to agree but these were all black painted glass envelope TO1 types. I did wonder if the white spot ones suffered from their thinner base thickness but none suffered from C-E shorts, only various open circuits.

Are OC44s seen as any less reliable over time than OC71s I wonder?

[Al (astral highway)]

Originally Posted by Herald1360

I wonder how frustrated hobbyists were back in the day trying to use these things with limited or no access to decent test equipment?

1975, I made my first audio stage for a crystal radio from a red spot transistor of some kind. Young teenager at the time.
It was tacked to a wooden base, point to point, following a design in a Ladybird book, I seem to recall, but I might be wrong on that one. (I also went to the reference library to photocopy Practical Electronics, but that build method stands out for that period).

The alternative was a huge brazing iron powered by a blowtorch. That was quite interesting until I got the knack of it.

[paulsherwin]

You have to remember that mainstream transistors were really expensive in the 60s. Hobbyists bought manufacturer's rejects because that was all they could afford. They were experimenting with them and were under no illusions.

[Nuvistor]

I used a few red spot and white spot transistors in the early 60’s, they worked quite well in simple radio circuits. Audio amps, TRF radios with reaction etc.
How well they would be in more complex circuits I can’t say.

[deswradio]

Paul is right - they were expensive. As a schoolboy in the 1960's I vividly recall buying yellow spot transistors (no part number, so probably manufacturers' surplus) from the local radio shop (Bold and Burrows, St Albans) for 3/6 each (that's 17.5p) - it felt like a fortune for a component so sensitive to over/reversed voltage and heat from the soldering iron.

Des

[G.Castle]

A couple of years back I bought a mixed junk box at an auction and there were about 25 of the Mullard M range OC 44 transistors in their original boxes, these were all good devices low leakage and hfe in the 70/80 range. I think that the SO2 glass package was Mullards finest achievement and the putty that the encapsulation was filled with was an effective environmental barrier as well, I've seen those transistors with broken cases still function. The white/red spot transistors were rejects that were then graded again by the hobbyist suppliers into guaranteed 'functional' and the cynically named 'untested types'.

[Herald1360]

I remember being bought an OC72 by Dad in the early '60s. ISTR it cost 7/6d (37.5p). It was used to build a Gilbert Davey one transistor amplified crystal set circuit from Boys Own Paper. That device plus another unidentified one scavenged from a commercial one transistor crystal set that my younger brother had no interest in went from project to project for a few years.


Then I discovered valves and free scrap radios and TV sets which kept me out of (in?) mischief for the next five or so years apart from a handful of free recovered used CV transistors from a schoolfriend whose father worked at the RRE.

[MotorBikeLes]

Herald 1360, it would be instructive to knock up a simple one transistor "something or other", with croc clips for the transistor, and see how many of the bad ones actually work.
A "one transistor" crystal set (without the crystal or separate diode) probably best, as that involves RF and AF.
Les.

[Herald1360]

I did wonder about knocking up a simple RC coupled amplifier stage on a bit of strip board with a transistor socket and poking it with audio and low rf signals to see what joy might be found. Possibly some of the devices characterised as two diodes with a common cathode might work to some extent. I doubt whether the single diode ones or the no component found ones would do anything though.

[MotorBikeLes]

Herald 1360, one thing that I suspect but am unsure of is what your "cheap multimeter box" is that you mentioned in your first post.
If it is one of the Chinese devices that recognises and displays parameters of devices, you must know that they simply do not "understand" Ge devices.
It was that thought that prompted my previous message.
I picked up the attached circuit as the first result of an internet search for "One transistor crystal set". It shows an npn si device, so at the least you would need to change cell polarity.
Maybe some of of those single diodes would work?
Les.

[ionburn]

I remember back then using a cheap Russian meter that had a transistor tester to test transistors of the day. I recently checked and found some of the transistors I tested back then, along with their results. I then re-checked them with the same meter, which I still have. Obviously no recent calibration but the results I got were pretty much identical to then. The transistor types included SFT307, as well as some red spot I have, and other Mullard germanium. As mentioned above by Les, a modern meter I used just didn't work.

[electronicskip]

i Have a dedicated transistor tester which came with a joblot of electronics stuff but ive never tried it,