[HN Gopher] Reverse-engineering the waveform generator in a 1969...
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Reverse-engineering the waveform generator in a 1969 breadboard
Author : picture
Score : 55 points
Date : 2022-03-09 18:04 UTC (4 hours ago)
(HTM) web link (www.righto.com)
(TXT) w3m dump (www.righto.com)
| kens wrote:
| Author here for all your questions about obsolete oscillator
| circuitry :-)
| adrian_b wrote:
| Even if I do not have any question, because I happen to be
| familiar with this kind of circuits, I just want to thank you
| for your work resulting in one more interesting article.
|
| I suppose that there must be many like me, who normally would
| not feel the need to comment your articles, but who nonetheless
| enjoy very much reading them.
|
| A long time ago, when I was young, I have worked with many
| devices and circuits similar to those reverse-engineered by you
| in this series of articles. Unfortunately at that time it was
| tedious and expensive to make photographic records of such
| technologies and such work, so now I am sad that I do not have
| records and the memories fade away.
|
| Your articles fill this void and I am grateful for them.
| tgflynn wrote:
| I'm curious how you were able to source the parts to replace
| the burned out transistors and other components.
| AdamH12113 wrote:
| Nice write-up! Question about the (excellent) schematic PDF --
| in the pulse trigger section, the emitter of Q3 seems to be
| tied to the top of R14, but I don't think that can be right? Is
| it supposed to be connected to ground?
| kens wrote:
| You should expect about 90% accuracy from the schematic :-) I
| didn't check the transistor part numbers, so I kind of
| guessed at NPN vs PNP. Most likely it's a PNP transistor. But
| the pinout could also be wrong.
| parksy wrote:
| There's a group in my city who meet every month to generate wacky
| noises from all sorts of things. With this thing's built-in
| generator and layout I feel like you could build a primitive step
| sequencer with those switches and dials and deliver a godlike
| performance of audio and engineering prowess.
|
| Even better if you can voltage control the frequency. Then if you
| can introduce a delay in the oscillator output, filter it, then
| feed back into the variable resistor(?) that controls its
| frequency, you have the basis of a mini-FM synth - if you can get
| it to stay stable in the normal human hearing range of course...
|
| Nothing really to add on the engineering side, just seeing how it
| looks, I want to hear it making some noise, although it's not its
| intended purpose.
|
| Nice work on figuring out how to get it going again!
| earthscienceman wrote:
| Which city and how do I join something near me? Denver?!
| scarecrowbob wrote:
| You might take a peek at the Colorado Modular Synth Society:
|
| https://www.facebook.com/groups/1216704935132398
| parksy wrote:
| Our local one is https://www.noizemaschin.com/ - they're
| based in London and Perth Australia, it's kind of a hybrid
| maker space / underground scene. Good folk from all walks of
| life.
|
| Not sure about Denver but I did some searches for
| experimental music, perhaps jump on the local subreddit as it
| seems there's a small noise music scene but I wasn't able to
| pinpoint anything specific.
| bragr wrote:
| I love the hand hewn charm of these old boards. Now even homemade
| boards are designed in software so everything is very straight
| and regular, but with old boards you can tell everything was done
| by hand from the design to the layout to the assembly. Don't get
| me wrong, it's great that you can cad something up, send the
| files off, and get perfect boards in 2 days, but these old boards
| are the electronic equivalent to a charming, rustic, cabin in the
| woods.
| thecloud wrote:
| If you buy a guitar pedal from a small-ish boutique company,
| you might just get a little box with a lot of charm that you
| can open up and peek at some beautiful hand assembled/soldered
| circuits :)
| gzalo wrote:
| Am I the only one that thinks that $1300 is absurdly high?
| acording to radioshack catalogs, in 1968 you could get an rf
| signal generator for just 30 bucks, and an oscilloscope for 130
| bucks, so why whould you spend that much in this breadboard? it
| doesnt seem like it would cost that much!
| kens wrote:
| I think that the signal generator is closer to HP test
| equipment quality than Radio Shack quality, which may explain
| the price. I was expected a simple circuit, but when I looked
| inside it turned out to be very complex.
|
| Here's the brochure for the breadboard with specs and the
| price:
| https://archive.org/details/TNM_Elite_1_2_3_dynamic_breadboa...
| amelius wrote:
| You can't get very high signal integrity on a breadboard.
| bragr wrote:
| Zooming in on the unit, the range knob on the function
| generator goes from 1hz to 1Mhz and the pulse generator 100ms
| to 100ns. I looked in a 1968 catalog a didn't see anything with
| close to those capabilities.
| https://radioshackcatalogs.com/flipbook/1968_radioshack_cata...
| ChuckMcM wrote:
| Lovely. And I really like the design aesthetic of the knobs and
| switches (similar to analog computers which I also find pretty
| fascinating). I've seen the variable voltage regular to change
| output amplitude trick in circuits where that signal is low
| impedance and designed to have a lot of drive current. One was a
| pulse generator that provided the signal for an animatronic
| robot, and the pulses were basically used directly to fire the
| solenoids on the pneumatics. Saved having a transistor on every
| solenoid.
| formerly_proven wrote:
| > The sine-wave shaper appears to be inspired by the similar
| circuit in the HP 3300A Function Generator, introduced in 1965.
| The schematic below shows the HP 3300A's sine-wave shaper; the
| breadboard's network is similar. The resistances are carefully
| chosen to achieve the sine wave.
|
| In some Philips FGs they had sine shaping ASICs (presumably with
| a ton of taps and good matching) and managed to get distortion
| down to 0.1 % iirc (which for the 70s or early 80s would have
| meant that you don't really need a proper RC oscillator any more
| for testing audio amplifiers).
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