455Khz filter on Tube Theremin a Question

[kagliostro]

Some years ago I build a pair of SS Theremin, at that time I collected also some Theremin Tube projects, one was interesting because of the absence of coils to be wrapped

In the circuit is present a 455KHz filter that I had a bit of difficulty to find

At that time I was able to contact the author of the project and he indicated me to search for a Murata SFU455A

Now I'm newly interested to that old project but till now I was able only to get an SFU455B not A filter

On the datasheet the SFU455A and SFU455B are near identical as spec, only .... only the SFU455A is indicated to be connected to resistors and the SFU455B to be connected to IFT (Intermediate Frequency Transformer)

The question is, can I use the SFU455B on this circuit or I must go on searching for the SFU455A ?

THANKS

Franco

[shooter]

don't see a problem electrically, the frequency tolerance of +/-2Khz shouldn't be much of an issue sonically

[kagliostro]

Ciao Shooter, thanks

Someone told me that the A version is an High impedance device and the B is a low impedance device

But I confess I understand nothin on such a circuit so I don't know what to think ....

Franco

[shooter]

buy it n try it.
the notes indicate the A) is used in a resistive circuit, B) for connecting to IFT, which I read as IF transformer, an inductive circuit.


for your application I don't believe it matters much.

[kagliostro]

At the moment I'm doing other, recently I got the SFU455B and so I'm asking if I can consider to stop the search for the SFU455A or must go on for that

(I was searching, and, by mistake, ordered the one I've now thinking it was the right item, I immediately recognized the error but decided to maintain the order on)

Franco

[PRR]

It may not matter. In radios we have to preserve the weak signal so we control our impedances. Here the signal starts large (probably most of the 48V DC supply) and seems to be attenuated by a large resistor. You might have to change the 1Meg into the filter.

Overall: I think trying to build a beat-frequency Theremin is masochistic/masochismo.

[kagliostro]

Many Thanks PRR

Good council about the reduction of the 1M resistor value

Overall: I think trying to build a beat-frequency Theremin is masochistic/masochismo

I'm not so skilled to really understand what I'm trying to do building one of those 

Only hoping it will perform right as it was previously builded and played

Franco

[shooter]

trying to build a beat-frequency Theremin is masochistic/masochismo.

had to analyze a beat circuit in the Navy, most everyone would break it down to it's mathematical model, I wrote something to the effect;
Fo enters the circuit, immediately get's a beat-down from 455Kz, after filtering out the garbage, the good sheet exits 

[PRR]

> Fo enters the circuit, immediately get's a beat-down ..

Cute, but in my limited experience, Theremins are all about Murphy's Law.

The part that always frustrated me on any wide-range (not Navy radio) beater is the tendency to sync-up and make no output, then JUMP to hundreds of Hz, with nothing between. "All you need" is incredible isolation filtering and shielding between the two oscillators, but not that easy to do.

I like opto-resistors. You can wave your hands, you can set them under a sun-dappled tree.

[kagliostro]

I think I've one other Tube Theremin project that seems interesting, if I find it in the archive I'll submit to you

Thanks to all for the consideration and suggestions

Franco