I'm restoring a Tek422 oscilloscope, and it uses a multi-vibrator circuit to drive the HV transformer. So in LTspice I tried the inductor values of a few mH and it worked and oscillated, somewhere just under 1mH, it doesn't osc.

When working it wasn't that nice of sqr.wave outputs, so I measured the real inductor values w/ an LCR meter, and they are only 720u and 730uH @ 10kHz (the real thing runs around 24kHz). And that doesn't osc. at all in LTSpice. So I added in the Rs/Rp/Cp and that doesn't help, nor does coupling L1/L2. At 100kHz they only measure ~50uH, I tried before I checked the repair manual for the wave freq. near 24kHz

I haven't tried AC analysis on this type of circuit before, but why would LTSpice be failing, because they aren't loaded so far in my circuit ? IDK the transmission parameters, I better learn that today too

 

? sure about the polarity of the diodes ?

What is the task this circuit has to perform ← the frequency tuning of such circuit may require additional chains !!

 

Are you sure those are the right semiconductors to use to model that oscillator? 2N3055 has a low fT and low hFE. I agree with ci139's concern about the directions the diodes are facing.

What transistors does Tektronix say are in the circuit?

While at it, what does the load for the output of this circuit?

 

Aren't L1 and L2 windings on a transformer? Isn't that an essential part of the circuit model?

 

EDIT:
A. Transistors 2N3055 do not produce good square pulses because
of their low F_t = 2.5 MHz.
For 2N2222 F_t = 300 MHz.
B. To prevent load current flow through transition C-B of Q1 and Q2,
should be used diodes D3 and D4.

 

The BJT's are RCA-40250 which has a gain of 25-100, and is used for the -12/+12V rails, so I figured 3055 is pretty close at DC anyways.

My spice model with basic 100ms trans. does't look near as sqr.w like at the top as Danko's, w/2n2222, and still doesn't work at the measured values. I'll see if switching BJT works. Or maybe restart spice, sometimes it gets messed up.

 

Yup Danko I had the diodes backwards, I need to learn this type of circuit. The HV trans output has a winding for the CFT heater, and the coil driving a voltage tripiller type circuit.

 

sometimes it gets messed

it gets messed when you have chips "linked" from one directory and you swap them (the same Model name) to be linked from another library . . .
. . . or if you modify and re-run the same circuit many ... many times . . . it gets slow

had the diodes backwards

it depends on diodes and on the required mode of operation ... using double forward Si rectifiers for current limiting is faster than some other means
— is why i asked about the purpose of the circuit