Interesting valve multivibrator circuit.

[Geordie McBoyne]

The attachment shows the type of multivibrator employed in the sync pulse and pattern generator that appeared in the June 1958 Practical Television magazine.  I've no experience of this type of oscillator. According to the designer it has excellent stability. Might have a go a constructing this circuit.
The valve is an ECC81.

Geordie McBoyne.

[ppppenguin]

I can't see how that circuit works. Where's the time constant? Unless V1 draws grid current C1 is simply a decoupler. Is C2 both coupling the sync pulses and part of the time constant?

The emitter coupled astable (a rather better design than the classic cross coupled astable) is different again.

This may be worth a very quick look. But only a very quick one
https://www.youtube.com/watch?v=Ul4iYmxVsaM

[pwdrive]

Explanation, mag page 777 onwards:

http://www.americanradiohistory.com/Arch...955-12.pdf

Lawrence.

[Kalee20]

That's interesting! I'd have had the same question as Jeffrey. But it makes sense.

[peter scott]

Is the confusion not that this is actually a monostable multivibrator whereas we are more accustomed to free running multivibs?

Peter

[Kalee20]

No, from the explanation it is a free-running astable. Probably nearest equivalent is a Programmable Unijunction Transistor.

[ppppenguin]

It's not a circuit you could emulate with ordinary transistors. Possibly with FETs where the gate can be forward biased and conduct to the channel.

[Terry]

This is how I normally visualise a cathode couple multivibrator:

   

[Murphyv310]

I built one of these many moons ago. Requires sync to start it then it will free run.
Not a practical circuit as it will ruin an output stage easily.

[Terry]

Which circuit are you referring to, Trevor?

I hope it isn't mine because it is the horizontal oscillator from the Bush TV85 and it didn't need kick starting, nor did it ruin output stages!