Roberts R707 batteries
 

I have been given a faulty R707 to look at by a friend but unfortunately someone has been at it and removed the battery connectors, directly wiring a PSU in their place. I was just wondering what the original battery arrangements were and what the supply voltage should be. The owner says it worked for a short while before going off, after the PSU was fitted by a technical person in a shop. It has Mullard modules inside so I suspect it will have the usual faults associated with those. Any advice welcome. Roberts radios aren't really my strong point.
Alan.

Re: Roberts R707 batteries
 

According to the service sheet, this set uses two 6V batteries in series with no centre tap.

Re: Roberts R707 batteries
 

They are lantern batteries, the springs on the battery connect with copper plates in the battery compartment.
Frank

Re: Roberts R707 batteries
 

Does this help?

Re: Roberts R707 batteries
 

Ah right, that would explain the gadget in the middle. That must connect with the batteries. For some reason I just assumed it would be some kind of PP3 arrangement. It looks like there was a DC connector on the side for powering the set up. This has been removed for some reason and is now hanging loose on the inside. I will check my CDs and see if I can find the service info. I have just got the set and hadn't got further than a quick look inside to check the damage. Thanks for the help. The original PSU was set for 6 volts so if the set requires 12 volts that wouldn't help with the performance. (PS Just seen the photo.) That's a great help. I see now how it all goes together.
Alan.

Re: Roberts R707 batteries
 

Hi.

Mark just beat me to it but attached are a few pics. Note the wood slat that spans across the two lantern batteries. This is not an original but one made from some available plywood, it needs to be stained black as per the original.
The R707 is a great radio when working but must be one of the worst sets to work on as it's very labour intensive dismantling everything to gain access to the IF module. Well worth the effort to repair though.

Regards
Symon.

Re: Roberts R707 batteries
 

I've retro-fitted my R707 with a couple of 1.2 Amp Hour lead-acid gel-cells wired in parallel; these will happily power it for 3 weeks or so of daily use before needing recharging [i like to turn the volume up to '11'].

Gel-cells make sense in this sort of application - the output-stage design and low-speaker-impedance of the likes of the 707 mean the power-supply needs to be able to deliver high current-peaks without suffering from voltage-sag.

Re: Roberts R707 batteries
 

Will you take them to the radio/cycle shop for recharging?

Re: Roberts R707 batteries
 

While the idea is appealing, I have one of these: http://www.sunpower-uk.com/products/...es/default.htm that does the whole condition-and-recharge-thing in four hours.

Re: Roberts R707 batteries
 

Did you fit a fuse in the supply to the radio?

Lead acid cells can supply high currents, enough to vaporise PCB tracks.