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Suggestions for parafeed OPT - Any guidance out there?
Suggestions for parafeed OPT - Any guidance out there?
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Old 15th February 2020, 01:28 PM   #21
mondogenerator is offline mondogenerator  England
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Accepted. Indeed I misused the LCr meter.

My apologies.

Thanks again.
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Old 17th February 2020, 06:59 PM   #22
mondogenerator is offline mondogenerator  England
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Now I have measured the impedance of the transformer I have been using I can confirm some facts...

Rather than quote an impedance ratio of 15k:300R, which isnt the full picture at all

Thanks to PRR for pointing out the obvious (test method that I cant believe I didn't think of myself), pointing out my obvious mistakes/assumptions.

Safe to say, yes I am foolish and spoke without thought.

The transformer in question has an impedance maximum of about 12k centred about 1kHz.

It's of fairly high Q, if that is the proper term to use. Impedance drops to less than 1k at each end of the BW.

I'd recently bought some small PC mount toroid to try with a similar advertised voltage ratio, but a 1.6VA in comparison to the 30VA I have been using.

Interestingly, these have a totally different impedance curve, and give a similar impedance maximum, and load well down 10Hz, with a turnover at somewhere between 500Hz and 1kHz..ending up about 1kOhm at 60kHz.

I'm not sure what I can glean from this...other than a transformer that has given me a reflected load of 12kOhm at 1kHz has worked well, at 1kHz

And the LNFB has done it's best to keep distortion in check, below and up until 1kHz at least.

Perhaps then I should aim for a better OPT around 12k:300, 25k:600, or the like?

Then hope the interwinding capacitance is low enough to keep impedance high, or move the peak higher in frequency?
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Old 23rd February 2020, 05:14 PM   #23
mondogenerator is offline mondogenerator  England
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Default And it goes something like this

Quite an interesting comparison between the original toroid, and the half of the smallest toroid I can find...

I wonder what use a second isolated primary winding would be?

A source for feedback?
A node to load with R or C perhaps, to tune the other windings?
Perhaps a source for Distributed Load connections- if I were using pentodes as pentodes.. ?

An answer (of sorts) always seems to generate more questions!
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