Electronic construction kits

[Mark Carver]

I had a Denshi Board

[Dave Plowman (News]

I remember seeing one - an audio pre-amp - which used skeleton controls (presets) for volume and tone, etc. Obviously not expecting it to last for long. ;-)

[Chris J Dixon]

A school friend had a No. 10, in a great big wooden chest. I had a 3, upgraded to 4, and I eventually got the gear set.

Chris

[Adrian]

In message <rob5s5$193e$ [e-mail]>, Martin Brown <'''newspam'''@nonad.co.uk> writes

You had transistors ?

I don't remember anything as exotic as transistors (this was mid 70s), resistors, caps, some form of tuning coil, an ear piece, some from of battery holder and a Morse key all rings bells, but I can't remember if there was anything more.

I've just looked up the X20, and from what I can see, it doesn't look much like what I had.

Adrian

[charles]

I had (and still have) the Mullard book "Transistors for the Experimenter" which was published in 1956! So yes, we had transistors in the 1950s.

[Tim Streater]

OC44, OC45 - RF amp stage OA81 - diode OC72 - AF pre-amp stage OC71 - AF amp to speaker

These were available in the 60s for AM radio kits - the ubiquitous tranny.

[Chris Hogg]

Henry's Radio, 5 Harrow Road, sold little MW radio kits in the late

1950's. I had one at boarding school. Great for listening to Radio Lux after 'lights out'. Remember Horace Bachelor, from K-E-Y-N-S-H-A-M, Bristol? The radios had a ferrite rod aerial and coil, a simple compression type trimmer capacitor fitted with a knob for tuning, and a hearing-aid earpiece. They white spot (RF) and red spot (AF) transistors, probably germanium. There were also yellow/green spot transistors, but I can't remember what they were for.

[gareth evans]

I remember a pair of OC81 in QPP (Quiescent Push-Pull with an OC81D as the driver for the splitting transformer.

[spuorgelgoog]

Aye, but at a price.

In 1964, Noyce estimated a price of about $4 at the time ($30 today).

That's half the price of $8 in the 1950s. You'd have had to be quite wealthy, and probably quite privileged too, to get your hands on a transistor in the 1950s:

"For 1953 information is unavailable, but total sales were probably somewhat less than one million units. Industry figures show over a million units sold in 1954. In 1955 sales were over three million units and in 1956, with the advent of new portable and hybrid auto sets, total sales could double. See Table 1 on page 41 for report on sales. Still this is only a small percentage of the total tube market which has averaged about 250 million units for new entertainment equipment alone over the last five years.

"The use of a transistor is, therefore, restricted to those applications where its advantages outweigh its increased cost. In 1953 they replaced tubes in hearing aids despite a unit price of over $8.00, because of the enormous advantages they offered in this application. In 1955 their use began to multiply in portable receivers, despite a price that averaged several times that of a tube, again because they possessed inherent advantages which were valuable in portable receivers."

Owain

[charles]

In the UK the situation must have been very different. I just went to a local shop which sold components. I was still at school, so not wealthy.

[Tim Streater]

Oh yes. And the H. Samuel 'Everrite' watch.

[charles]

His Infra-Draw method.

and MacDonald's Chocolate Penguins

[Max Demian]

Rather posh. White spot for RF, red spot for audio pre-amp, green for power output to the speaker.

[Dave Plowman (News]

Think you got the last two the wrong way round, Tim. The OC72 was the output one.

You can still buy them. About £4. One of the few transistors that costs more LSD than when current. ;-)

[tabbypurr]

I wasn't around in the 30s either, but I sort of lived through it for a while where not much had changed since the 30s.

NT

[tabbypurr]

way too expensive for kids' kits back then.

[Martin Brown]

Germanium ones with rubbish gain ~50x and lots of leakage. The PNP AF116 was actually quite fast for its day too but the NPN AC127's were less good but could handle a modest amount of power (ISTR a whole 500mW).

ISTR the even older electronics kit had a Mullard OC71 PNP as its sole transistor. I recall scraping the black paint off it to make it into a more expensive light sensitive phototransistor (aka OCP71).

I can't recall the exact date but it would have been around 1968. By the early 70's I was playing with 741's and red LEDs. We had an electronics club at school. The physics master was building a digital clock from scratch. Dismantling scrap ICL1900 boards for ICs A = 7400 etc. I got quite good at desoldering without breaking any legs off the chips.

I used to get given a few "ruined" ZTX300/500 transistors off the Ferranti fab line at the start of the production run. The first always had shorts and slag bridging their leads. I learnt most of my electronics from their applications notes and those of Signetics.

That is a still a good basic introduction to bipolar transistors circuits even now. Unlike Wireless World most circuits in there work!

[Martin Brown]

In the 50's yes, but by the mid to late 1960's there were even better transistors about so that the OC7x, AC127 and AF116 were affordable.

ISTR blowing one up was still an expensive mistake for a schoolkid.

[Tim Lamb]

Memory lane.. For reasons best known to my employer, having shown no specific aptitude and studying electrical engineering at college, I was moved to the electronics dept. for my final 2 years as an apprentice. I think the *whizz kids* who actually knew something had moved elsewhere. The dept. had previously used Mullard Norbit gear but was moving to an in house logic system using the Texas Instruments germanium switching transistor 2G302. Based on a *plug in* system using an 8 pin valve base and with timers, delays, pulse units etc. it provided an easily repairable/adaptable system. I got sent all over England and Wales doing the on site commissioning. TI discontinued production on the 2G302 and we changed to an equivalent NKT218 from Newmarket Transistors. Also quickly discontinued so we had to change the supply polarity and use silicon NPN.

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