Ekco CR280 valve/tube car radio, 1950s

Hook a high voltage ps in place of the rect tube and get the radio playing before working on the vib circuit. Ken

contacts

so on

hint of

making

?

load to

heaters

loss

Yest that sounds a sensible plan of campaign

Unfortunately both bell-mechanism and rectifier would seem to be in the vibrator module, and transformer is external, shown in lowest view of the pic.

a recently uncovered Ekco "bill hoarding" from the 50s Cobden Bridge/ Bitterne Triangle, Southampton, England

Unplug the rect. tube. Connect B+ to the B+ of the radio, usually the rect cathode. Remove the vib and connect the proper dc to the battery lead of the radio. Turn the set on and check for the proper B+. Do you have a regulated supply, and have you replaced the electrolytics in the power supply? Ken

CT160.

next

the

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

Vibrator searchword in Google veered off in other directions but other than this, nothing found

Wright & Weaire Ltd.

Owned by Joseph Wright & Thomas Weaire is famous for it's tape deck mechanism that formed the nucleus of the Ferrograph, Vortexion, and Clarke & Smith range of tape recorders. Wright & Weaire Ltd or WW as they became known, started manufacturing radio components from a factory in Tottenham, London in 1922. Long before the concept of the tape recorder was invented.

........

Other items manufactured by the company were electrical devices for field radios. Most notable of these was the "VIBRATOR" powered from a DC battery, it chopped the current derived and fed it into a transformer to step it up into an AC voltage, for use by portable field radio equipment. This produced a high voltage AC, from a low voltage source.

By the end of the war Joseph Wright & Thomas Weaire announced their decision to retire and offered the company to Richard Merrick, Ernest Niblett and Walter Berridge (the company secretary) on advantageous terms and they accepted this offer without hesitation.

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

some

loose

won't

Rectifier-less circuit magic presumably by this circuit

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 
http://home.graffiti.net/diverse:graffiti.net/

Made up an umbilical and a variable raw HT1 supply. So 12V dc from normal bench supply feeding heaters and with vibrator removed some HT feeding DC to HT1. Strange dealing with radios marked in metres, I expect the Home Service rather than the Boomtown Rats coming through. Needs alignment, as very good response 1900 to 1500 metres but poor down the

1000m end. Works, sort of, with HT1 of as little as 50V. Took valve base dc readings on HT1 = 160V, as a bit of a lash-up. Works perfectly ok at 260V ,on the end of band that is, but will try sorting out the vibrator first before taking any full HT readings.

With a 100mA fuse protecting my HT transformer plus variac I have to start low and build up or the fuse blows but otherwise current of 27mA at HT1 of

50V, 27mA at 160V and 44mA at 260V which is as expected

I only have alignment plus schema for similar Ekco car radios of the period, not this particular one. Anyone know if the data from these people

usually contains alignment details ?

--
Diverse Devices, Southampton, England 
electronic hints and repair briefs , schematics/manuals list on 
http://home.graffiti.net/diverse:graffiti.net/

removed

the

dc

sorting

period,

The mechanism of the HT vibrator is mostly covered with soot? but not the sponge liner shown in the third image, how come ?.

The small rattling piece is a contact that has come detached from position to the left of the purple \ and shown in isolation as the black dot on the second image. The adjustable frame contact is just above the purple \, coil to the left. The vibrating strip is central terminated with the iron bob next to the coil pole piece.

How to clean up and how to re-attach the contact pad ? presumably epoxy will not survive the temperature. Can opened easy enough and room inside for a pouch of activated silica gel before closing and epoxy coat sealing.

--
Diverse Devices, Southampton, England 
electronic hints and repair briefs , schematics/manuals list on 
http://home.graffiti.net/diverse:graffiti.net/

Yup, that's a synchronous (self rectifying) vibrator all right. You can get a solid state replacement from these people:

Jeff

A factoid about synchronous vibrators - a radio using one is polarity- sensitive. That is, if the radio is negative ground, you cannot run it positive-ground. If you do, the power supply will generate "B- negative" instead of B-plus, putting reverse polarity on the filters (smoothers). But a radio using a tube rectifier will run OK on either ground polarity. Most will even run on AC, but with some wierd 'beat' effects with the mains frequency.

Now a synchronous vibrator *can* be used with opposite ground by simply reversing the two transformer secondary leads that would normally go to the plates of a tube rectifier.

Useful to know that polarity reversal point for a future occassion. This is a positive earth only radio, no user switch, going back into (another + ground) such old vehicle.

The contact is 4.4mm across and I have successfully robbed a contact from a

20 amp relay which is about the same size. Hopefully will be able to swage it (with a ball bearing and vice) into this mechanism after grinding out the copper back pad of the original. The spot weld ? had failed between the platinum? pad and copper back pad.

If this all fails then solid state it will have to be.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

you might wish to silver solder the contact - use the low temp solder from a jewelry store and a propane or acetolyne torch

** Posted from **

If I get this thing going again , anyone know how to adjust? Obviously must get the right sort of HT under load but beyond that ? Minimised 12V current consumption? balanced switching waveform ? minimum noise ?, minimum sparking? relative immunity to less than 12V supply?

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

I wouldn't like to do that job too often. Found out why there was ohmic path on one of the contacts. Insulating plastic sleeve around one of the bolts had burnt and charred, shows how hot the contact arms got. Some of the high temp sleeving for 1/4 inch spade connectors just about fitted there. Had to replace the mating contact as that had a great crater in it as well as the broken one. Had to remove one standard rivet and replace for to be able to get to the covered contact, to replace it.

Then reassembly is a pig as dozens of bits of mica etc . Will try powering tomorrow.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

Sounds like the buffer capacitor died. Something in the range of

0.001 uF or so but with a 1 KV rating. When those die, bad things happen to the contacts.

Jeff

hot

I'll change that before powering up.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

One thing you'll need to do is try to get close to 50/50 duty cycle, to prevent stairstepping the transformer that follows into saturation.

-

----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA

-----------------------------------------------

I replaced the 4nF, 800V on the HV secondary with 4.5nF 4KV. Testing the old one, it did not like 500V of a megger up it , it went short.

Radio is now working all on 12V , but not sweetly, as no can around the vibrator and no casing around radio and no screen at the final EL42 output valve. Sparking on any of the contacts is barely noticeable even in a darkened room, I expected quite a show. Adding 500 uF to the HT made no difference to the hash , so hopefully due to lack of screens. Vibrator on 12V , current unlimited, it produces HT of 300V cold ,dropping to 210V in use. Upping from 12V to 13V then HT goes up to 250V or so in use. Will have to wrap it up in all its casing just to check the output is like the audio with a proper mains HT before adding an FM IC and secret switches, which was the original idea.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

rt.

t

to

g

se.

e

es,

Kudos, great job! 'Specially on having the points running with little visible fireworks. The hash should quiet down with shields in place.

Bill(oc)