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Old 23rd Apr 2021, 5:45 pm   #1
Top Cap
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Default Roberts! - It's a bit late for an April Fool.

I just bought a Roberts R707 that was reported to be dead. Opening the back I found no battery clips and all supply wires were terminated onto a power input socket not shown on the circuit diagrams I have. So the radio needs an external supply but at what voltage? The circuit diagram shows 2 x 6V batteries in series to give 12 Volts. This seem very plausible because the voltages given are no higher than 12 Volts. But the descriptions I have read, call for 2 x PP9's to be installed! So I am in a bit of a fix here as I do not usually handle Roberts as I do not like their construction methods and their use of those 'orrible modules.
But I thought help was at hand because sitting in the middle on a steel base plate was a weird looking module. Perhaps this is a regulated power supply? Possibly rectifiers and smoothing to take an AC input?
The box looked very small for that but I decided to remove it for investigation, after all maybe this was why the radio was non working? Now this was not too easy as it is held in place by three metal 'twist' posts which were very difficult to untwist. When I eventually removed it and saw what was inside the mystery box, I very nearly fell off my workbench chair. It is just a piece of wire, presumably a fuse, with no indication of rating! But what an incredibly stupid idea to make an enclosure like this. A simple in-line fuse holder of the type fitted to car radios would surely have done the task or maybe it was the cost of the fuse that forced this crazy design. Talk about a late April Fool Joke!
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Old 23rd Apr 2021, 6:00 pm   #2
Restoration73
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Default Re: Roberts! - It's a bit late for an April Fool.

I think that even if you fit 2 x PJ996 batteries the tinned copper wire won't melt. even
if the radio went s/c. With the cost of batteries, it's hardly surprising they fitted a socket
for external DC.
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Old 23rd Apr 2021, 6:30 pm   #3
ronbryan
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Default Re: Roberts! - It's a bit late for an April Fool.

The box is the mechanism they use to interconnect the PJ996 Lantern Batteries - the ones with coil springs as contacts. The Lantern Batteries are quite cheap at Electrical Wholesalers and do last a long time in a R707.

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Old 23rd Apr 2021, 8:16 pm   #4
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Default Re: Roberts! - It's a bit late for an April Fool.

Actually I have just checked out the circuit and the piece of wire is completely out of circuit, it is connected to pads that are completely open circuit. You could not make this up, anyone else found this?
An external 12v supply brings the radio into full life so the problem of no operation and the reason for sale must have been a faulty power supply. I only paid 10 for the radio and expecting to open up the LP1164 at least, so not a bad deal I suppose even with the April Fool box.

Just seen your replies and it finally makes sense. I would never have thought that two lantern batteries would be required.
Perhaps Roberts realised they would last longer?
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Old 23rd Apr 2021, 8:25 pm   #5
paulsherwin
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Default Re: Roberts! - It's a bit late for an April Fool.

It was an odd design decision to use lantern batteries, but I don't think Roberts were the only manufacturer to do it.
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Old 23rd Apr 2021, 11:41 pm   #6
Paul_RK
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Default Re: Roberts! - It's a bit late for an April Fool.

The only other I can think of is Decca in their very early transistor models, the TP22 in a cloth-covered case with a handle on top and TT33 which was the same radio but veneered and presented as a table set.

As for the R707, it was in production for several years and was only fitted with a DC input jack in its final year or two.

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