> I first tried to find some info on the vibrator to confirm it does have
some
> sort of rectifier inside.
> > The vibrator has some large slightly loose lump in there and a small
loose
> something if turned end over end it rattles to the other end, but I
won't
> try going inside.
> >
> > I warmed up the mastic/putty on the vibrator enough to scrape off with
> > mark-one scrapers to reveal.
> >
> > Wright & Weaire , London
> > Synchronous (self rectifying) Type QFA/12 12 volts vibrator
>
> Vibrators. Self rectifying. A "special" case of vibrator.
> (I noticed in the picture, it had 6 pins.)
>
> Normal vibrator: a vibrating contact that turns the DC to
> the transformer on and off rapidly (about 180 Hz) to make
> the transformer think it's being fed AC and allow it to
> transform it up from 12 volts up to 200 or so. These will
> have a rectifier, like a 0Z4 (gas filled diode, no filament)
> that converts the AC back to a DC voltage.
>
> Self Rectifying: Also known as synchronous. Extra contacts
> on the vibrator switch the polarity on the input of the
> transformer back and forth rather than just on and off. In
> addition, a second set of contacts switch the secondary of
> the transformer back and forth, so that it appears to be
> DC to the filter capacitors. No rectifier needed.
>
> So, in your case there is no rectifier to locate and remove.
> it's "magic" and part of the vibrator operation.
>
> That being said, the basic advice is the same. Remove the
> vibrator and power the radio from an external B+ (HT) supply.
>
> That makes the radio a LOT easier to troubleshoot and get
> working again. (Although, I would automatically replace ALL
> of the wax paper capacitors and the electrolytic filters
> before working on the radio.)
>
> Once the radio is working, then you can concentrate on the
> power supply (vibrator) issue. And I would suggest buying a
> solid state replacement for the vibrator.
>
> Jeff
Rectifier-less circuit magic presumably by this circuit
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feeding back output pulses
from a Quarrington book , 7 pin minimum agress with what I have here, 7 pins, and wiring back to the transformer agrees. So just coil of 28 ohms DC and 2 pairs of contacts in the case. It hums quite happily so I will assume it is OK for the moment and crack on feeding some decent, known good, DC into the radio
s.e.d added if anyone there may be interested
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
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