Re: Ekco CR280 valve/tube car radio, 1950s

> 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

formatting link
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

formatting link

Reply to
N_Cook
Loading thread data ...

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.