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[burakkucat]

I'll point you to the plug-in regulator that is present in the Type 706 telephones. The regulator can either be in circuit or removed from circuit just by pulling its small PCB out, up-ending it and plugging it back in the "other way round".

See Note C in diagram N806.

I wonder if the regulator has been taken out of circuit? 

[sevenlayermuddle]

Thank you, I will take a closer look at the regulator.

With reference to the following page (should show a 706 'tear down'), the regulator PCB appears to be present, and the right way around.  That doesn't exclude the possibility that, for some reason, it's not working right.  Further analysis will have to wait for daylight, availability of time, and full sobriety. 

www.britishtelephones.com/t706dismantle.htm

I note the author of that article is credited as  Sam Hallis, consistent with the link you posted. 

[sevenlayermuddle]

I think I am going to conclude my sidetone is within normal limits.  The main components affecting it seem to be R1, R2, C1B, the regulator and the transformer.  Main suspects would be the resistors and capacitors, but the Rs are close to value, as the is cap, and the cap' has no obvious leakage path.

I have however fixed a minor defect... In reply 36 to this thread, I mentioned the nostalgia of 'hearing the dial pulses'.  Looking at the circuit diagram, they're not meant to audible - the receiver being shorted out by a pair of dial contacts when it's off rest.

A brief and gentle wipe at the affected dial contacts with abrasive paper and a coating of switch cleaner has rendered the pulses near-silent, as they should be.  Don't ask me why they are not totally silent, I guess the dial contacts are not quite achieving 0 ohms.  But I do seem to remember it was not unusual to hear very faint pulsing in the receiver when dialling, so I think I'm going to leave well alone.   

[burakkucat]

Thank you for the update on your examination and refurbishment.

I can well remember a two tone green Type 706 telephone (PCB version) from the early 1960s and needing to disassemble/reassemble it. But I can't remember the reason why . . .