E.A.R. Battery Operated Record Player

[af024]

Well here I am again trying to get another battery-operated record player going.

This one is in a real mess.

Faults so far …
One winding on the transformer was o/c. I was lucky here and I managed to find the end of the fine wire and re-terminate it.
One of the OC81 output transistors was duff. Replaced ok with second hand one.
Someone’s fiddled about and added the fawn-coloured cap on the right (box shaped) – I’ve left this for the moment.
The motor was seized up and electrically o/c too (carbon brushes stuck in holders). I was unable to open motor (moulded together), but I managed to exercise it with small amounts of machine oil and loads of jiggling about. I also managed to remove terminals (which double up as carbon brush holders) and free off the brushes. Whilst I was there, I extended the small springs a bit to give more pressure onto the commutator.
The speaker rattles (nasty).
The rubber idler wheel gone hard and is also mis-shaped (probably due to it being parked hard up against the motor pulley for years). This is a bit of a problem methinks.
The battery terminals are corroded.
The paintwork is going rusty.

So all in all a bit of a mess.

Anyhow, I’ve managed to get both amp and the motor running ok and the cartridge seems ok (phew!).


The whole thing was nothing more than a kit of parts. I supposed I should have thought a bit longer as to why things rattled when I first picked it up! I simply couldn’t resist though.

Anyhow, before I go any further along the restoration path, I have a few mysteries that I’d love to hear your comments on …

See the underside picture -
Let’s assume that the amp is meant to be mounted on the small stand off pillars (which seem to align ok – no others do).

Let’s also assume that the on-off/volume control is also meant to be mounted through the hole bottom right (seems reasonable).

Well this is when things go wrong. The wires from the amp to the pot are simply not long enough (and interestingly, unlike most things, they don’t look tampered with).

Also, there is no dc blocking cap between the output of the amplifier and the speaker. As things stand, the speaker would be connected between +ve batt and the junction of the emitter/collector of the two output transistors (OC81s).

Could the orange Plessey capacitor be the cap in question, or is this just to strap across the motor?

Fundamentally, I wonder if this is the correct amp for the player?

Why is there a 180R resistor soldered across the L/S terminals?

Interesting eh.


Andy

[peter_sol]

Hi
Do you have the model number ?

[af024]

There lies the problem. Apart from the E.A.R. logo, there's nothing else that I can see I'm sorry to say.

Andy

[Darren-UK]

There's a picture of one of these at http://www.dansettes.co.uk/battery.htm where it's described simply as an 'E.A.R Portable'. Maybe contacting the owners of this website would reveal more information ?

[af024]

Thanks Darren, I've dropped them a line via their website and keeping my fingers crossed for some photos.

Regards,


Andy

[Nickthedentist]

Originally Posted by af024

Also, there is no dc blocking cap between the output of the amplifier and the speaker. As things stand, the speaker would be connected between +ve batt and the junction of the emitter/collector of the two output transistors (OC81s).

I wonder whether the correct battery arrangement would have been "centre-tapped" with one terminal of the LS being connected to the battery's mid-point?

[af024]

I don't know. Good point though. The remains of the battery compartment wiring would suggest that it uses 6 x size D cells all connected in series. But then someone has got at it, so that's nothing much to go by. I guess I should try and draw out the circuit.

Regards,


Andy

['LIVEWIRE?']

I used, many years ago, to have one of these EAR Players. Unfortunately I neither remember the model no., nor have a circuit diagram. I suspect the amplifier was the usual transformer coupled type, with OC71, OC 81D = 2 x OC81. 6 'D' Cells(or U2s as they used to be called then!)were used, and the centre tap may well have connected to the speaker

[af024]

Thanks Livewire.

I'm well on the way to sketching the circuit out now. It uses 2 x OC72s and 2 x OC81s. Back soon with the result.

Andy

[af024]

Well here's the circuit (as best I can make out) - I hope I haven't made any mistakes.

Regards,


Andy

[peter_sol]

Hi you need a cap in series with the speaker poss 100 uf at 16 or more volts otherwise the bottom transistor is effectively shorted out
or perhaps it is there and the speaker is connected to the wrong place.
Regards
Peter.

['LIVEWIRE?']

Looking at the diagram I suspect that there should be an electrolytic capacitor of, possibly 220 or 470uf between the O/P Transistors and the speaker, negative to transistors. I don't know why there is a resistor accross the Loudspeaker, either, unless its' to protect the transistors in the event of speaker failure.
(Peter, you just beat me to the same conclusion re the speaker coupling capacitor!)

[Herald1360]

Not sure about the output biassing arrangement.... I would think that the bottom connection of the winding connected to R11 should connect to the collector of TR4, not the emitter, and the top end of the winding connected to R10 should connect to the emitter of TR4, not the collector, if the bias resistors really do connect direct to the bases.

Normally this sort of amp has the four bias resistors in a string from + to - with the driver windings carrying the bias current from the taps on the bias string into the transistor bases.

Chris

['LIVEWIRE?']

I would agree with Chris about the biassing. Thought I had a circuit diagram for the amplifier used in the EAR 'Autobat' which used a similar amp., but I can't find it.

[Paul_RK]

Here's the Autobat circuit, but it doesn't look especially similar as four-transistor amplifiers go.

Paul

[af024]

Thanks for your comments guys. I will double-check my sketch just in case I made some mistakes. As for the speker connection, well I got the whole thing as a kit of parts and the speaker isn't connected to the amp. There are flying leads from the speaker, but they are simply not connected to the amp. Studying the amplifier further, I can confirm that there is definitely no other capacitor lurking on board - only the large orange Plessey on the tag strip. One of the connections looks like it should go to the point on the PCB marked O/P. As for the other connection, well I assumed the +ve batt connection.

Thanks for the Autobat circuit Paul - I'll download it and print it out.

Regards,

Andy

[af024]

Well Chris, you are absolutely correct. Upon closer inspection, the circuit is as you described. Thanks for that.

I've posted an amended drawing below.

Also, and this really is surprising, C5 appears to be inserted in reverse polarity. The +ve side really is connected to TR2 e - no, honestly! Surely that's so wrong?

I still can't resolve the mystery of the missing capacitor for the L/S. There's no space for one on the PCB. Ah well, I could just strap one somewhere - perhaps hang it off a L/S terminal?

One final thing, does it matter whether the speaker returns to +ve batt terminal or -ve? Probably not.

Regards,


Andy

['LIVEWIRE?']

The negative side of the Electrolytic on the tagstrip should be connected to 'O/P' point on PCB, and the positive side to the Speaker -ve, with speaker +ve to chassis

[af024]

OK, that's how it will be then thanks.

Just got to find a suitable L/S and idler wheel replacement now (and re-wire to make everything reach to where it's got to go). I wonder what sort of impedance?

Oh, AND reverse C5!

Cheers,


Andy

[peter_sol]

To help identify the unit
What is the cartridge type?
Regards

Peter.