Dr Ronald Stiffler SEC technology

[Lidmotor]

Nick and All----Here is the basic SEC-15 build diagram that I used to build my first SEC many years ago.   The L3 is the same as on a SEC-18.  The author of this diagram called the coils L1, LB, L2 but they were really named 1,2,and 3 by Dr. Stiffler.

---Lidmotor

[erfandl]

Yes, it can help you.  And you can always add fix capacitors in parallel with it if the 120 pF is not high enough.  (Of course the setting range suffers.)    You may have access to old AM pocket radio in which a plastic cased variable capacitor can be found, normally such has 2 x 260 or 2 x 300 pF variables.    Or you collect a range of fix capacitors like 22, 47, 100,  200 pF and place them in parallel in gradual combinations.

thanks. its helped by parallel 22pF with 30pF trimmer and circuit is now working, but the inductors gets very very very hot !

[gyulasun]

Hi Erfandl,

Very good your oscillator is now working.

Is the transistor you use is hot too?  Is the base resistor 100 kOhm or 1 MOhm now?

Please use a DC Ampermeter to learn about the input current your oscillator takes from your voltage source
(the 3.7V battery?). If this current is less than say 30-40 mA, than the hot choke coils can be explained as follows:
the ferrite material these chokes use is not powdered iron but hard ferrite and their performance above a certain
frequency becomes gradually lossy and more lossy, this loss manifests in heat. Very likely the oscillator frequency
went up to the several 10 kHz range where the chokes ferrite material becomes extensively lossy.
If you happen to have a digital multimeter which can measure frequency, hook it between the collector of the transistor
and the negative supply rail to learn about it.
IF this core loss is the problem (i.e. the current consumption is not in the hundreds of mA range), then you need to
obtain 1000 uH  (1 milliHenry) chokes that has no ferrite material.
Gyula

[erfandl]

Hi Erfandl,

Very good your oscillator is now working.

Is the transistor you use is hot too?  Is the base resistor 100 kOhm or 1 MOhm now?

Please use a DC Ampermeter to learn about the input current your oscillator takes from your voltage source
(the 3.7V battery?). If this current is less than say 30-40 mA, than the hot choke coils can be explained as follows:
the ferrite material these chokes use is not powdered iron but hard ferrite and their performance above a certain
frequency becomes gradually lossy and more lossy, this loss manifests in heat. Very likely the oscillator frequency
went up to the several 10 kHz range where the chokes ferrite material becomes extensively lossy.
If you happen to have a digital multimeter which can measure frequency, hook it between the collector of the transistor
and the negative supply rail to learn about it.
IF this core loss is the problem (i.e. the current consumption is not in the hundreds of mA range), then you need to
obtain 1000 uH  (1 milliHenry) chokes that has no ferrite material.
Gyula

no transistor isn't hot only inductors hot. the current is 720 mA  frequency is 85 kHz. resistor is 1M ohm.

[gyulasun]

Well, then the 720 mA is the problem: it can happen when the isolation between the plates of the trimmer capacitor
is damaged and there is a short circuit somewhere between the plates.  Remove the battery i.e. switch off the oscillator
and with your Ohm meter check resistance between the two pins of the trimmer capacitor.  IF the trimmer capacitor or
the 22 pF itself is conducting as quasi a piece of wire, then chokes L1 and L3 can get hot (but the L2 choke in base
is not hot, right?).   Maybe the circuit board itself has become conductive somewhere?
It is interesting the oscillator is able to work.  Do you use the 3.7V battery?