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[conradelektro]

Theory concerning 4 transistors in parallel versus just 1 transistor:

The base of a transistor is also a small parasitic capacitor. Having 4 transistors (4 bases) in parallel will multiply this parasitic capacitor by 4. A charge will accumulate in this capacitor and it will flow into the one transitor that triggers by chance as the first one (the other 3 will not trigger and at each cycle an other transistor of the four transistors could trigger but my guess is that always the same triggers due to very fine diferences in the production process).

The charge is sufficient to trigger one transistor if it is accumulated in 4 bases but is not sufficient if it can only accumulate in one base.

Putting a 1nF capacitor in parallel to the 1-8K base resistor should do the same. May be a smaller capacitor of e.g. 500 pF will be better.

Greetings, Conrad

[gyulasun]

Hi Conrad,

If I may chime in here,  no need for thinking that the 4 transistors in parallel may behave esotheric. The 4 in parallel has 2 useful benefits: the resultant drain-source channel ON resistance becomes 1/4 of that of a single transistor so that the power loss (I*I*R) due to the smaller channel resistance is also 1/4 only.
The second benefit is that the resultant forward transconductance (or forward transfer admittance) (dVgs/dId) becomes 4 times as high than that of a single transistor. 
So the reason for paralleling them is to improve manufacturing "deficiences" on certain important parameters for an oscillator. Of course unwanted parameters also occur when paralleling: input and (output) capacitances get also 4 times as much, this would not be needed at all...  should a device in a circuit need higher input capacitance, you could always add some to see any benefit.

Here is a data sheet for the 2sk170:  http://www.audiodesignguide.com/DACend2/2sk170.pdf  and you can order cheaply from futurlec.com for instance.

Greetings,
Gyula

[conradelektro]

Hi Conrad,

Here is a data sheet for the 2sk170:  http://www.audiodesignguide.com/DACend2/2sk170.pdf  and you can order cheaply from futurlec.com for instance.

Greetings,
Gyula

@Gyula: thank you for your input. Looking at the data sheet I see a "reverse transfer capacitance CRSS" of 6 pF. So, a 22 pF capacitor parallel to the 1-8 K base resistor should do the same. But there might be the other considerations you mentioned. It has to be tested, theory is just words.

Greetings, Conrad

[scratchrobot]

Be sure to try all combinations of coil connections before you change other stuff. Say you have coil A with connections 1 and 2, and Coil B ditto.
So you have 4 possible ways to hook up the coils; two should work and two won't, and of the two that do, one might be a little better.

Thanks but i tried every possible way but nothing was working for me. I will try again tomorrow and also hook up a scope to see if i get oscilations. Not easy testing this with one finger on the peltier, Magpwr where are you  ;-)

[TinselKoala]

Thanks but i tried every possible way but nothing was working for me. I will try again tomorrow and also hook up a scope to see if i get oscilations. Not easy testing this with one finger on the peltier, Magpwr where are you  ;-)

Test with a stable voltage source like a regulated power supply or a battery. When the circuit works, then sub in the Peltier.