New to solid state...will this circuit work - Page 1
Forum section: electronics / beginners

author: Planobilly
author_rank: Regular Contributor
timestamp: May 25, 2021, 05:36:58 pm
content: Hi,This should be super simple but I am having trouble getting it to work. Can one of you just confirm that you thing the circuit is valid.One of the issues is junk crap from ebay. I will never buy another component that did not come from Mouser or DigiKey.I have a small tester that says that pin one is the emitter. The transistor in question is marked 2N2222A-331. The Motorola datasheet says pin one is the emitter. On Semiconductor says pin one is the collector.I recently got some JFETs from Amazon that were marked as JFETs but were actually NPN transistors. My little amp project worked after I ordered JFETs from Mouser.Thanks,Billy

author: Zero999
author_rank: Super Contributor
timestamp: May 25, 2021, 05:52:30 pm
content: Yes, that circuit should work. Are you sure the polarity of the LEDs and capacitors is correct?

author: Grandchuck
author_rank: Super Contributor
timestamp: May 25, 2021, 06:16:28 pm
content: It is possible to run across transistors like the P2N2222A where the E and C leads are reversed from what most consider normal. Unfortunately, some transistors (such as ebay "bargains") have the wrong part numbers on them. You can identify the leads with an ohmmeter, by the way.

author: Planobilly
author_rank: Regular Contributor
timestamp: May 25, 2021, 06:23:15 pm
content: At 73 anything is possible...lolI am building the circuit for the second time and checking the value of every component.I am placing the transistors in a removeable fitting so I can change things without re-soldering.Yes, I understand where the anode and cathode are on a diode and what is positive and negative on a electrolytic cap.I will report back when I get the new circuit built with photos. I have both digital and optical microscopes so reading the fine print is not an issue.ThanksBilly

author: james_s
author_rank: Super Contributor
timestamp: May 25, 2021, 06:26:03 pm
content: I remember building multivibrators like that on a breadboard when I was a kid. It should be easy to get it working and component requirements are not critical at all, any old random junk parts you find ought to work. If the parts on each side are not matched then the flashing will be lopsided but it will still work.

author: BrokenYugo
author_rank: Super Contributor
timestamp: May 25, 2021, 07:02:27 pm
content: Trust the little tester for pinout, nearly any NPN will work for this.

author: Planobilly
author_rank: Regular Contributor
timestamp: May 27, 2021, 01:48:48 am
content: No one should have to work this hard to get a couple of LEDs to flash. After the second try...https://youtu.be/shfqsSa_fUAThis is built on a eyelet board the same way 1950's guitar amps were made...lol old school to the maxThanks for all the helpBilly

author: james_s
author_rank: Super Contributor
timestamp: May 27, 2021, 02:10:24 am
content: There you go, that reminds me of the ones I built as a kid, I used larger capacitors so they flashed slower though. The same circuit can be used with much smaller capacitors to generate audio tones. What ended up being the problem? Wrong pinout on the transistors?

author: Planobilly
author_rank: Regular Contributor
timestamp: May 27, 2021, 03:14:39 am
content: I am not 100% sure. I used 2N3904 Transistors this time. I may go trouble shoot the old circuit tomorrow to see if I can find the fault.I have built and repaired dozens of tube guitar amps so a jump into solid state should not be that difficult. I think the biggest issue is knowing for sure what the pin out of something is.Having parts by known mfg with datasheets will go a long way to making this a less troublesome learning curve.ThanksBilly

author: james_s
author_rank: Super Contributor
timestamp: May 27, 2021, 04:59:33 am
content: If you have one of those component testers you can get the pinout of any transistor, you just have to trust what it tells you. A multivibrator like this ought to be very forgiving, it will work with the cheapest crappiest Chinesium transistors you can find as long as they behave vaguely like a transistor.Solid state is easy, at least low voltage stuff like this, it's a lot less exciting if you hook something up wrong.