Found the audio generator I built as a 16 yo - Page 1
Forum section: electronics / projects

author: ivaylo
author_rank: Frequent Contributor
timestamp: August 30, 2014, 02:38:32 pm
content: Mid 80s. I remember being fascinated by modular designs and etching a PCB to fit in a socket but have completely forgotten that couldn't find a coupled 10K potentiometer and had to build it out of two singles. Must have been much more patient than nowTurns out damn thing still works.

author: wraper
author_rank: Unknown
timestamp: August 30, 2014, 03:06:42 pm
content: Soviet germanium transistors, metal film resistors and multiturn pot + Bulgarian electrolytic capacitors and red film cap, not sure about brown one... mhmm, was your dad Russian spy?

author: Balaur
author_rank: Unknown
timestamp: August 30, 2014, 03:09:57 pm
content: Really good construction. Nice job.How did you made the PCB? Some kind of paint or pitch/resin mixed with gasoline and applied with a dip pen? Or maybe some transfer stuff? Looks good and nicely laid out. You even included component refs.I find the combination of Russian components and English on the front panel amusing. Did you got reported for that? Did a nice but stern tovarish from the Party had a good talk with you?Ah, so many good memories! Good old germanium MP39, the russian-sized DIN-5 connector that was mostly compatible with its german cousins, the bakelite button and the rather nice resistors, much better than some other est-european stuff where the pins were soldered to the body and risked falling out if over-enthusiastic application of heat from 100W soldering guns monsters.Good stuff. Thank you for sharing.

author: charlespax
author_rank: Regular Contributor
timestamp: August 30, 2014, 03:22:43 pm
content: The most beautiful thing I've seen all day!

author: ivaylo
author_rank: Frequent Contributor
timestamp: August 30, 2014, 04:17:37 pm
content: QuoteWow, you do know your obsolete parts!QuoteNope, I was a Bulgarian teenagerQuoteThere were two alternatives for the ink/paint:- Asphalt Varnish(?) with benzine as a solvent (struggling with the translation here, black nasty stuff I see they still use to seal outdoors metal or concrete surfaces, resists most acids, etc. For this the local edition of the Rapidograph pens (not Rotring or Staedtler but the lower quality locally produced equivalents) worked beautifully, just had to clean them fast.- Nail varnish with acetone as a solvent. For this you did need a dip pen (or even just a sharpened wood stick) because the acetone would screw up anything plastic.And two alternatives for the etchant:- ferric chloride - it was hard to get, you needed to know someone in a electronics lab or something (like most things communist you had to "know someone somewhere")- diluted hydrochloric acid - surprisingly this was easier to get (there were folks working in the nearby chemical plants)Looking at the fine lines I must have used a Rapidograph with asphalt varnish and probably hydrochloric acid.QuoteYup, I haven't seen the thing more than 25 years now, but believe it or not memories started coming back. The design came from a Russian book (or a magazine?). I think I only bought the electrolytics and the pots. The transistors were given to me by a friend of my dad. The transformer is what we called a "bell transformer", every house had one for the door bell (220V->9V). The PCB socket came from an old East German mini computer which we had to salvage at school. But the whole project got really inspired because I found the best aluminum box in the world (again, you couldn't buy things then, had to "find" them)...

author: Balaur
author_rank: Unknown
timestamp: August 30, 2014, 05:24:19 pm
content: Quote from: ivaylo on August 30, 2014, 04:17:37 pmsmola! (forum doesn't let me use Cyrillic characters)This is exactly how I did it myself as well. For the dip pens, I was using some kind of dip ink pen included with the Chinese compass sets.Dovizdanie!

author: wraper
author_rank: Unknown
timestamp: August 30, 2014, 05:24:41 pm
content: that brown cap is bothering me, isn't there K73-9 written on the opposite side?

author: ivaylo
author_rank: Frequent Contributor
timestamp: August 30, 2014, 06:29:11 pm
content: QuoteWhere are you really from?I know what smola is and I guess this is exactly what this was, but it was thinned down and they sold it (this was one thing you could actually buy) in 1L glass bottles. If you do read Cyrillic this guy still sells it (in bulk though) -http://vulkov.com/asfalt.html. And thanks for reminding me for the Chinese compass sets, we did use those for PCBs as well!QuoteNo, they are only marked with their values (1uF/250V in the case of the large ones). Only the one facing on the picture is stamped with MPT-96 (cyrillic 'P') on top. All salvaged parts, the brown ones are either Bulgarian or Russian, not sure.

author: Vgkid
author_rank: Super Contributor
timestamp: August 30, 2014, 08:33:04 pm
content: That is really well made, congrats. I wish I picked up building electronics earlier in life.

author: eneuro
author_rank: Super Contributor
timestamp: August 30, 2014, 09:33:52 pm
content: You must have redundant tracks or PCBs there, while those yellow marked and on other photos too looks like there is no copper layerHow electric current flows without wires in those circuits?

author: mzzj
author_rank: Super Contributor
timestamp: August 30, 2014, 09:43:15 pm
content: Quote from: eneuro on August 30, 2014, 09:33:52 pmIn soviet union you don't control electric current, the current controls you

author: IO390
author_rank: Regular Contributor
timestamp: August 30, 2014, 11:20:43 pm
content: Quote from: mzzj on August 30, 2014, 09:43:15 pmYou can see the trace, it's just a bit corroded.Edit: Forgot to mention, awesome job!

author: ivaylo
author_rank: Frequent Contributor
timestamp: August 31, 2014, 04:55:15 am
content: QuoteYeah, things are coming back to me. I was thought at the time after etching and cleaning/sanding the board to actually paint it with rosin flux dissolved in IPA. I believe we are seeing the effect of that after almost 30 years (not sure who came up with that idea). Luckily the tracks are wide and I am not measuring any difference in resistance between those and the good ones.QuoteI did pick it up early but then abandoned it for software. Now am trying to get back to it but looks like things have changed a little

author: calmtron
author_rank: Regular Contributor
timestamp: August 31, 2014, 11:18:37 am
content: Beautiful build, love the wiring harnesses and the socketed board

author: eneuro
author_rank: Super Contributor
timestamp: August 31, 2014, 12:35:27 pm
content: Quote from: mzzj on August 30, 2014, 09:43:15 pmIn soviet union air control was the most important thing, but their propaganda had to work hard to hide its crimes...It looks like history repeats those days and as well as it was not possible to investigate air crash of Polish flight in Russian Smolensk 2010, it is very difficult to do everything with MH117 shot down not far away from Russia border this year...http://en.wikipedia.org/wiki/Malaysia_Airlines_Flight_17"The Boeing 777-200ER airliner lost contact about 50 km (31 mi) from the Ukraine–Russia border and crashed near Torez in Donetsk Oblast, Ukraine, 40 km (25 mi) from the border."

author: ivaylo
author_rank: Frequent Contributor
timestamp: August 31, 2014, 03:47:34 pm
content: QuoteErr.., sorry to hear that a toy I built as a kid evokes stories of mass murder; jeesh...