Tickler (Armstrong) audio oscillator CPO

Not having any luck with the Knight CPO circuit:

https://wb9kzy.blogspot.com/2025/03/still-fiddling-with-knight-cpo-circuit.html 

 (probably the wrong transformer, I wasn't able to figure out the spec'd impedances) I found a similar circuit in the Raytheon Transistor Applications booklet, page 35, by Lou Garner:

source: https://tubes.mit.edu/6S917/_static/2024/resources/raytheon_transistor_applications.pdf

Also found data for the UTC SSO-3 transformer 10k ohms to 200 ohms (it also says 25k ohms to 500 ohms):

source: http://www.bunkerofdoom.com/xfm/UTC_1960_WEB/030.jpg
 

Since I don't have the CK722 I used a modern 2n2907 instead.  I looked through my parts on hand for similar audio transformers, finally found this Xicon TL006:

If the output center tap is used the result is a 20k ohm to 500 ohm transformer which is fairly close to the UTC transformer.  I tried it and it does work:

used a microswitch (on the left) as a key

However the tone isn't that great, volume is OK for phones.  With the 1k ohm Trimm dynamic headphone the circuit used 0.012 mA at 9 volts with this waveform:

 

With a piezo the circuit used 0.017 mA at 9 volts:

Neither is ever going to be mistaken for a sine wave - the circuit works down to 1.5 volts but doesn't sound as good as at 9 volts.
 

The circuit was worth a try but won't be using it in the future.

Best Regards,
Chuck, WB9KZY
http://wb9kzy.com/ham.htm