Simple transistor electronic keyer for qrp help - UK Vintage Radio Repair and Restoration Discussion Forum

Malcolm T · 4th Feb 2024, 2:28 pm

Built it then re-built it , checked all components and connections , changed transistors but to no avail, the only things i do not have are the 3.3 uf caps so i,m using 10uf would this really make a difference , its just not working .
It seems like a good circuit adapted from an astable multivibrator .
Does anyone have any clues why this would not work?.
See the third circuit down from top of page.

https://www.abcelectronique.com/annu...r-astable.html

Radio Wrangler · 4th Feb 2024, 3:52 pm

The wrong capacitor values will reduce the keying speed by a factor of three.

If one or both of the capacitors is leaky, operation is going to be prevented.

The astable multivibrator like that has a bug. Depending on the gain of each transistor, there is a possibility of both transistors turning on at once.

Some voltage measurements are needed to get any chance of seeing what's going on. It's a good candidate for one of the newer digital storage scopes.

A good example of the very simple circuit if you count components, but which can be very difficult to get going.

David

Malcolm T · 4th Feb 2024, 6:35 pm

Thank you, i will see if smaller caps do the trick first, looks like a search in the junk box.

4th Feb 2024, 2:28 pm	#1
Malcolm T Hexode Join Date: Dec 2018 Location: Lugo, Spain Posts: 483	Simple transistor electronic keyer for qrp help Built it then re-built it , checked all components and connections , changed transistors but to no avail, the only things i do not have are the 3.3 uf caps so i,m using 10uf would this really make a difference , its just not working . It seems like a good circuit adapted from an astable multivibrator . Does anyone have any clues why this would not work?. See the third circuit down from top of page. https://www.abcelectronique.com/annu...r-astable.html

4th Feb 2024, 3:52 pm	#2
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,924	Re: Simple transistor electronic keyer for qrp help The wrong capacitor values will reduce the keying speed by a factor of three. If one or both of the capacitors is leaky, operation is going to be prevented. The astable multivibrator like that has a bug. Depending on the gain of each transistor, there is a possibility of both transistors turning on at once. Some voltage measurements are needed to get any chance of seeing what's going on. It's a good candidate for one of the newer digital storage scopes. A good example of the very simple circuit if you count components, but which can be very difficult to get going. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

4th Feb 2024, 6:35 pm	#3
Malcolm T Hexode Join Date: Dec 2018 Location: Lugo, Spain Posts: 483	Re: Simple transistor electronic keyer for qrp help Thank you, i will see if smaller caps do the trick first, looks like a search in the junk box.