Help Please -- very strange oscillator problem

On Friday, September 15, 2017 at 2:12:54 PM UTC+10, snipped-for-privacy@gmail.com wrote :

You may need a faster oscilloscope. Many weird oscillator problems turn out to be an oscillation at a higher frequency than you can see.

And note that not all 2N3055s were created equal. The RCA originals had con tained a lot of silicon and were slow and hard to blow up. Other manufactur ers worked out how to fit the data sheet with less silicon, and their parts were faster and easier to blow up.

George H.

A schematic would be helpful. ...Jim Thompson

Schematic?

The 2N3055 is a power transistor, typically takes milliamps of base current and can deliver amps of emitter current, but at frequencies where air core coils work best, it's low in gain. It could be as simple as transistor high-frequency gain variation.

You should be able to check most components without unsoldering. At least I suspect that is true. Without a schematic , it is really a guess.

My guess is one of the transistors is not working. So how much trouble is it to swap the transistors and see if the problem follows the transistor?

Dan

please show schematic here in ascii art or some website.

It's probably a variation on this circuit:

which in my experience is a PITA to get to work correctly at the best of times. It's bad don't use it

I would be happy to supply a schematic, but then would need an email address. This Google group does not allow attachments.

Don't the coils need protection diodes across them?

Go to my website, click on the envelope icon. Do NOT attach anything, just send an E-mail. I will reply with an E-mail address you can use to send the schematic. ...Jim Thompson

We use something like Dropbox, or a photo posting site. Or make an LT Spice schematic and include the .ASC text in a post here.

Sounds like a blocking oscillator. this circuit?

this might be worth a look

Thanks, yes I have did have in mind a Royer oscillator in mind in the past, but shelved it after I could not find a straightforward way to implement the transformer with the feedback coils.

My existing problem is that one implementation of my oscillator workd fine, but the identical copy does not.

No, my circuit is is a loosely related to the last one at :

I did all that, but when trying to send the email with the schematic as attachment, I got an error message that the mail server was not responding.

Please take a look at a fairly close relative of my oscillator, the last one at :

I never got you initial E-mail (without any attachment) ??

That would be _your_ E-mail server.

Check to see if you have the diodes reversed. ...Jim Thompson

The circuit shown does have a stable state: both transistors saturated and nothing going on.

But it's impossible to analyze a circuit defined as loosely related to some other circuit.

There is an interesting, recurring psychological effect in our business: people describe the way a circuit can work, and ignore the many ways that it might not work.

Indeed! I have a client right now arguing with me about such a "state machine". ...Jim Thompson

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