IF Transformer Inductance Sanity Check

I see a lot of talk using 455khz IF transformers when an actual Theremax uses a 796 kHz I believe. Also the sine wave frequency in the graphic above seems closer to the 796 kHz. I have never modeled any circuits so I may be missing something. I use the plug & play method of parts with the minimal necessary  math. Then sniff for smoke!

The 42IF201 to ~203 have an internal 180pF capacitor in parallel to the primary winding which sets the resonant frequency around 455kHz.

But the 42IF1xx series as used in the Theremax have no internal capacitor, so that the circuit designer is free to choose the resonant frequency by adding an external capacitor. In the theremax pitch oscillators 100pF are used, and 68pF for the volume oscillators, if I remember well.

"If its a Hantek, you wont be dissapointed (not saying you should be dissapointed if its not, LOL!)"

I bought an OWON SDS7102V.  It is supposed to have a better A/D than other Chinese scopes but the SW is lacking - I'm banking on SW updates.

"I bought a cheap Hantek DSO1060 a couple of years ago (2ch 60MHz) and used it for a couple of months before I got sick - It was (is) great!"

Fred, sorry to hear about your health issues.  I hope your situation improves and you will be able to continue your work and to help us newbies.

Thanks,

Greg

"But the 42IF1xx series as used in the Theremax have no internal capacitor, so that the circuit designer is free to choose the resonant frequency by adding an external capacitor. In the theremax pitch oscillators 100pF are used, and 68pF for the volume oscillators, if I remember well."

Thierry,

You have a good memory!

"Fred, sorry to hear about your health issues.  I hope your situation improves and you will be able to continue your work and to help us newbies."

Thanks Gnsmith.

I will be here when I can - about another week, then I go to hospital for biopsies and possibly surgery - I hope to be back some time after that!

My main aim in returning was to dump a load of my ideas here so that, if worst came to worst, it would not all be wasted - but it is taking me a lot longer to sort out my piles of schematics etc into some form others could make use of, than I had expected - and there are a lot of other things I should really be doing as higher priority.

Fred.

My reply to RS Theremin (Christopher) has been moved to Here.

I posted about the Hantek DSO1060 'scope, and how good I thought it was..

Well, it died -  out of warranty.. Its only had low usage, I estimate each hour probably cost me about £6 if I cannot repair it.

Hantek are a complete waste of time when it comes to support - On the forums (Oh, I should have checked forums before buying the damn thing!) there are loads of people with the same or similar problems - no answers or help from Hantek.

I think I have possibly located the problem (dodgy crystal) .. but cannot be sure yet - I have a full set of test gear - other 'scopes, logic analysers etc, and its taken me a day so far to get to this point of a possible suspect. Most people who buy a 'scope like this dont have access to the kit I have.

Based on my expierience I now strongly advise people not to buy this scope - Or, quite frankly, any other Hantek product.

Fred.

>> Update:

I fixed my 'scope .. Dry joint on one of the crystal cans.. One of these damn RoHS problems where removing lead from solder means that large items like crystal cans dont wet properly, so after time oxidisation causes the contact to deteriorate. Big relief -

But my advice re Hantek still stands - They really dont seem to give a damn about their customers.