Single Transistor Amplifier Circuit Help

No surprise. It's not the cleverest experiment I've ever seen.

Graham

I take it you are talking about the second circuit, with an output transformer.

Are you using a transformer that has worked before, or did you purchase one new, for this experiment?

Are you sure you have the leads on the transistor correctly sorted out?

Have you checked that you don't have the two resistors switched?

Same question but about the capacitors.

Have you seen the note about what the dots mean where two lines cross?

Thanks for your suggestions...I bought new transformers.

I actually have a question about the transformer. There are three leads going in and three going out...but on the circuit diagram, there are only two output gates. Is this normal...if so, which outputs should i use...I've been using the top and the bottom one, disregarding the middle one. Should I tie that to the ground....or am i doing something wrong.

I'll recheck the capicators and resistors....

but does this circuit look like it should work?

thanks,

Trevor

This worries me. Since the transformer should have been designed for a speaker on the output side, I'm wondering if this transformer is the right one. I gather from the schematic that they want a 1k primary and an 8 ohm secondary for audio frequencies:

:

I looked at the picture there and, looking closely, it appears to only have 5 wires. The red and white should be your audio 8 ohm side and the green, black, and blue should be your audio 1k ohm side. Further, the second link above shows:

Frequency response: 300Hz to 10kHz 1,000-ohm center-tapped primary 8-ohm secondary

Note that they don't mention the phrase "center-tapped" in the case of the secondary.

I think you got the wrong part. The page you mentioned lists the Radio Shack part #273-1380. Are you sure you got that one?

Jon

Transformers can be made in almost infinite variety, with the windings turn count the main variation. The circuit you are building needs a transformer with at least one center tapped winding, that is made to connect to a 1k source, in order to make the positive feedback work in the audio range. The second winding has to have many fewer turns, to drive a speaker without loading the transformer so much that the oscillation stalls out. If your transformer has 3 leads at both ends, I am doubtful that it has one end designed to drive a speaker. Do you have any specs on the transformers you have, so far?

It is very similar to the very first transistor circuit I built about

It is a fairly forgiving circuit, if you have a transformer that even comes close to what is specified. Back in the days when 5 transistor radios were in everyone's shirt pocket, it was easy to pull the output transformer out of one and build this circuit. The center tapped primary (for a 2 transistor push pull stage) to speaker output transformers are harder to find, today. Where are you getting yours?

I got mine at RSR electronics...thanks for the suggestions--I'm going to go and buy that transformer and try it in the circuit.

Check the website at

He has some fantastic simple amplifier circuits that are tested and will work great. Also,

has some fun stuff for you to build (and also all circuits tested and work fine)