Advertisement

Blog

Oddities – Toss ‘Em Out or Keep ‘Em?

One of my colleagues, Michael Dunn (editor-in-chief of Scope Junction), posted pictures of some of his favorite displays that have gone the way of the buggy whip. His article, “Grampa, Tell Me About Old Displays,” is a good read. But don't read it now — I have more interesting stuff here. I thought about sending him some pictures of some of my “antique” electronic devices, but he said I wasn't allowed to send him pictures of radio tubes. I insisted I would never publish picture of tubes merely as a cheap attempt to get people to pay attention to Planet Analog.

So, having set aside that concern, I found some devices in my junk box. These parts are now just old and in the way. They were purchased for projects once planned and then abandoned.

Down at the bottom of this page, you'll see a picture of some of my oddities. There's plenty more where these came from. For now, we'll just have a quick look at five pieces.

I had a surprising number of old diodes. One that is pretty typical was made by RCA and was part of a line of general purpose replacement devices it made. These devices usually had part numbers that started out with “SK.” The one shown is a Zener diode. The next device is a UJT (unijunction transistor) made by GE Semiconductor. UJTs could be used to make oscillators — they had properties that were unique — rather like a comparator combined with an SCR.

This circuit came from my very old GE Semiconductor data book (long since out of print).

This circuit came from my very old GE Semiconductor data book (long since out of print).

Next is a medium power SCR from Motorola, an SCR316-4 in a stud-mount package. The next part in the odd-looking dual-inline package is a small audio power amplifier. It has extra copper tabs sticking out of each side to help remove the heat. See below for an applications schematic for the TDA810, a functionally equivalent part.

A typical applications schematic for the SGS-Thomson TDA810 (from its long since out of print data sheet). Thomson took over some of the RCA semiconductor devices when RCA got out of the business.

A typical applications schematic for the SGS-Thomson TDA810 (from its long since out of print data sheet). Thomson took over some of the RCA semiconductor devices when RCA got out of the business.

Oh, and then there is that DSP from ADI. I don't quite recall the details for the device. I believe it had a Zerk® grease fitting so that special high-speed lubrication could be pumped in to help the device operate as fast as it did. I could be wrong about that.

A portion of my collection. Zoom! The grease makes it go fast.

A portion of my collection. Zoom! The grease makes it go fast.

16 comments on “Oddities – Toss ‘Em Out or Keep ‘Em?

  1. Michael Dunn
    February 19, 2013

    Thanks for not posting any vacuum tubes…

    Re the SHARC…hmmm…you need to keep separate junkboxes for your different hobbies. Otherwise, there's no telling what might happen.

  2. eafpres
    February 19, 2013

    Do you have any tubes of that high-speed electronic grease left?  You can probably sell it for a fortune on ebay.

  3. Brad Albing
    February 19, 2013

    Well sure. but they would need a grease gun with a matching fitting. But I can't as it would be wrong to use this platform for my own gain.

  4. Battar
    February 20, 2013

    The TDA800 and TDA810 were very popular in the 80's – they turned up in intercoms and DIY projects everywhere, as well as in a few TV's. Any where you didn't see one, you found an LM380 instead.

  5. Brad Albing
    February 20, 2013

    And I've used the LM380 also. Nice little amplifier.

  6. JeffL_#2
    February 20, 2013

    Actually UJTs weren't very complicated, they're very much like SCRs with a little extra thrown in. And all SCRs are is a pair of NPN-PNP transistors connected base-to-collector with the PNP emitter referred to as the SCR “anode” and the NPN emitter as the SCR “cathode”. The node containing the NPN base is commonly referred to as the “gate” but technically it's the cathode gate, the PNP base would then be the anode gate. So now you simply add a resistor divider and connect the anode gate to the junction of the resistors. You connect the “low” end of the divider to the cathode and label it RB1, and bring out the “high” end of the divider and call it RB2, and the “anode” is now called the base of the UJT. Then you give the ratio of the voltage divider the fancy name “intrinsic standoff ratio”. So now you connect this UJT into a series RC circuit (resistor to supply, cap to ground) so the “base” goes to the RC node, then RB2 goes to the supply and RB1 to ground. This becomes an oscillator because the cap charges up through the resistor until the “anode” goes one diode drop (the EB junction of the PNP of course) more positive than the “anode gate” (the voltage at he divider node), then the “SCR” fires discharging the cap, the SCR then runs out of current and “unfires”, and the cycle starts all over again. You can actually usee two transistors and a voltage divider to substitute for a UJT in those old application circuits. These devices (and the folks who came up with them) were clever but the “technology” certainly isn't very mysterious.

  7. jkvasan
    February 23, 2013

    I had used 2N2646 UJTs in my thyristorised non-mcu DC Motor Drive. This was during end of the 80s.

    Some ICs worth mentioning are

    Audio : LM386, TDA2822

    Triac Dimmer : CA3059

     

  8. karenfield
    February 25, 2013

    On behalf of the wives of techies everywhere, please STOP encouraging the practice of keeping every blasted odditie. My house already looks like a Cabinet of Curiosities! Thank you.

  9. Brad Albing
    February 25, 2013

    On behalf of engineers everywhere, let's try to avoid gender stereotypes. It could be the chick engineers who are keeping these old/odd curiosties.

    Besides which, it would a crime against humanity to throw away an old Wheatstone bridg or a 01A triode.

  10. Michael Dunn
    February 25, 2013

    🙂  Yeah, I'd love  to meet a chick engineer  with a good collection of oddities. We could start a museum!

  11. Brad Albing
    February 25, 2013

    Uh-oh….

  12. Michael Dunn
    February 25, 2013

    What's that? You want to donate to the museum?

  13. SunitaT
    February 28, 2013

    Brad, thanks for sharing pictures of “antique” electronic devices. I am curious to know if those devices still work ?

  14. amrutah
    February 28, 2013

    I my college days, we studied about the schottky, zener, varicap diodes, Unijunction transistors…  Though the zeners, schottky and varicap diodes are still used for many applications, while the Unijunction transistors (which we had used to build oscillators) are less heard or used.  Do you foresee and applications for UJT's or will it die in this MOSFET era??

  15. Brad Albing
    February 28, 2013

    I believe they do still work. I'll check later.

  16. Brad Albing
    February 28, 2013

    I'm pretty sure the UJTs will be completely gone in a few more years.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.