TV horizontal oscillator coil

[roadster]

I am looking at a new small project based on a circuit in a 1955 QST, ARRL magazine.
One component required is a  100 mH, adjustable (TV horizontal oscillator coil, GE type RLC-091 or equivalent).
I know nothing about TVs, never actually having owned one, so would like some advice on a possible equivalent coil. The value is not critical, even a fixed approx. 100mH centre tapped coil would be ok. It is low power and AF.
Here is a link to the circuit: https://www.robkalmeijer.nl/techniek/ele...index.html
Thanks in advance for your help.
Rod

[BusyBee]

Someone here with TV experience may have good guidance. As noted it is a Harley oscillator with tuning to give variation in tone. At a push the tone could also be varied, if a fixed tapped coil is used, by a variation in the capacitance across the tuned circuit but you would need to juggle a few figures to get an idea of range. Varying the capacitance with those values would probably have to be switched rather than variable. Personally I have tended to use Colpitts oscillators at such low frequencies as they don't require a tapped coil but obviously it would mean a different circuit. Another thought I have is whether two 50mH coils would work Ok as the tuned circuit is still effectively 100mH (two 50mH in series) and the tap can be taken between the two. My theory gets a bit iffy as regards Q and suchlike at this point though. All in all a nice original design would maybe look best (thinking aloud here so worry not about the rambling and ignore if a distraction).

I will re-iterate though that there are a few people here who will have ideas on the coil.

Tracy

[roadster]

Thanks Tracy, I am am not sure about using two separate coils, in case the two halves of the winding acts as an auto transformer, these look as though they may be suitable but I am not sure if they are two 100mH windings or if the total is 100mH:      https://uk.rs-online.com/web/p/leaded-in...s/8711521/.
Once I have the tone I like, the frequency can be fixed, so trying various values of capacitor wouldn't be a problem. I liked this particular circuit for its simplicity.
Rod

[ppppenguin]

Why not try some odd mains and audio transformers from the junk box. I doubt you can do any harm. Don't worry about exact centre tap. 2 separate coils won't work. They must be coupled.

[jimmc101]

While I'd agree that coupled coils are normally used, I'm sure that coupled coils are not required, after all a Colpitts oscillator doesn't use coupled capacitors.

See   Analog.com for a practical example using non coupled coils.

[url=https://wiki.analog.com/university/courses/electronics/comms-lab-hartley-osc][/url]



Jim

[roadster]

Thanks for the replies, I have some small 1:1 audio transformers, I will try one of those for a start, wiring the pri. and sec. windings in series and hopefully in phase first time! If that works I will try using two of them just using one winding on each to see if coupling makes any appreciable difference. I will reoprt back.
Rod

[BusyBee]

I did think about the chokes you mentioned, when I glanced around for options, but was unsure. The transformer idea sounds a good one. With my oscillators I have used those small inductors that look like resistors, although at radio frequencies, but another option maybe, if limits are observed. With my circuits, although valve, I tend to work at somewhat lower voltages.

Tracy