Thanks, gentlemen.
Edited, added : The genuine circuit is :

Unsure about the windings phasing. Cell is 1.3V.

Will build the circuit presented by Danko; which is somewhat similar and will report findings.

The resistances measured in the working transformer 0.5 ohm and 43.6 ohm corresponding to Xicon part number 42TU008. (Of course not available at Mouser)
Worth to try ordering for evaluation. Was $2; now $50+ in the robbery trend. [ Dimensionally, 42TL008 is nearest similar ]

 

Thanks, gentlemen.
Edited, added : The genuine circuit is :
View attachment 283990
Unsure about the windings phasing. Cell is 1.3V.

Will build the circuit presented by Danko; which is somewhat similar and will report findings.

The resistances measured in the working transformer 0.5 ohm and 43.6 ohm corresponding to Xicon part number 42TU008. (Of course not available at Mouser)
Worth to try ordering for evaluation. Was $2; now $50+ in the robbery trend. [ Dimensionally, 42TL008 is nearest similar ]

View attachment 283985
View attachment 283986

Find the closet match and I’m sure you can tweak other values to get it to work! Very nice!!

Paul
KI5VNH

 

Unsure about the windings phasing. Cell is 1.3V.

Using diode D1 is necessary.
Without diode, pulses 400 V are present on base Q1.
EDIT:
Circuit below is changed according to information in post #25:

 

I am still a bit unclear as to what the goal is. At first it appeared that the OP wanted to reproduce an audio oscillator from the 80s that used a transformer like this, but had no published information on...and then he linked to another post on this forum, which is what others have described as a Joule Thief / blocking oscillator...and now we come full circle to a pseudo-sorta sine wave generator with this transformer again.

Voltage it needs to run on is...?
How long should it last, if on battery?
What is the required frequency (range)?
What output level are we looking for either out of the circuit or into what appears to be the only constant in this post, an 8 ohm speaker?

Do we have any of these details? I did read the previous posts and it isn't clear to me...

Paul
KI5VNH

 

Thanks, Paul.
You are very correct, I skid off the exact subject because found a similar schematic while searching and was distracted if that would work. Please pardon me. The one in pencil was made by observing this brutally simple gadget original.
- Works on 1.2 to 1.5 V. AA cell. The second cell installed has lasted like 15 years so far, because is a continuity tester tool that
- oscillates at 1 KHz and
- increases frequency with just a few ohms or fraction! of an Ohm added in series to the speaker. Seems that 33 Ohm resistor sets the lowest frequency of about 1 KHz, loud enough to hear across a room. Adding just a few ohms to it increases the frequency like 100 Hz. Can tell by ear how good a connection is. Pushing the probes harder into the solder joint of a circuit is enough to change the tone.

It has been extraordinarily helpful to me to locate poor or corroded contacts, cold solder joints and poor conductance. Probes are in series to speaker. Consumes zero battery current unless probing. No on/off switch. It may appear irrelevant and vulgar circuit, but enjoyed and admired its performance for ~30 years, with nothing similar behaving better. Continuity testers in the market or built-into multimeters are no competitors. Not made any more and want to make a spare one, refusing to pay $100+ used! Tried with many transformers and do not work equal, cannot discern why.