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Old 1st Jul 2006, 11:22 pm   #1
PJL
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Default Whistling Roberts R200

My car boot bargain has shown it is always wise to look a gift horse in the mouth.

I have some reception but it is quite weak and I get a lot of whistling. This is the earlier OC44/45 model which I believe does whistle a bit but I expect a few capacitors are not doing their job. There are a mix of electrolytics and some moulded capacitors that look possible culprits. Any advice on which ones normally need to be replaced?

Then do I remove the existing capacitors and substitute new ones or try to leave them physically in place and solder new ones underneath?

I plan to re-align the set when I'm done - is it a 465KHz IF?

Last edited by Darren-UK; 23rd Jul 2007 at 9:47 pm. Reason: Keeping thread to specific topic.
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Old 2nd Jul 2006, 11:04 pm   #2
Tim
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Default Re: Whistling Roberts R200

Hi Pjl.

Any wax capacitors or Hunts Moldseals should be suspect. I have found those Plessey electrolytics to be faulty on a couple of occasions. Check the one across the battery. Also check the circuit diagram to make sure the driver transformer is correctly connected.

Re lack of sensitivity. Check the coils on the ferrite rod haven't moved, or see if moving them along the rod improves things.

Good luck,
Tim
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Last edited by Darren-UK; 23rd Jul 2007 at 9:43 pm. Reason: Keeping thread to specific topic.
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Old 3rd Jul 2006, 9:17 pm   #3
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Default Re: Whistling Roberts R200

It's a shame to destroy the look of the set with new capacitors but I am not going to the effort of hollowing out the old ones and I think in common with most on this site, I am more interested in getting it to work as well as it did when new.

Last edited by Darren-UK; 23rd Jul 2007 at 9:45 pm. Reason: Keeping thread to specific topic.
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Old 4th Jul 2006, 8:44 am   #4
Geoff G4ICD
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Default Re: Whistling Roberts R200

Quote........
It's a shame to destroy the look of the set with new capacitors but I am not going to the effort of hollowing out the old ones.....

It takes seconds to saw off the -Ve end of the Hunts cap, drill a hole in it for the new leads, pull out the old internal junk, drop the new cap in the body and with a little sealer job done, worth it as it still looks the same as it came out of the factory...........
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Old 9th Jul 2006, 11:05 am   #5
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Default Re: Whistling Roberts R200

I took a scope to the set and sure enough the OC44 osc./mixer emitter showed a ringing/modulated mess. Replacing the emitter bypass capacitor fixed it so I have replaced the other moulded caps as well. On my DVM they all measured around 4x the original value but I suspect this is missleading.

These caps are brown moulded D.C.C ones. The only option I can think of would be to fill & paint the new yellow ones?
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Old 9th Jul 2006, 11:32 pm   #6
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Default Re: Whistling Roberts R200

D.C.C =Dubilier capacitor co.
If these are the little grey ones with rounded ends, these often go faulty too.
I change these as a matter of course too. Some of the later Dubilers were found in 60's and 70's tellys, and weren't much better.
I Well done for finding the fault. Sometimes the old 'scope comes in handy!!
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Old 17th Jul 2006, 11:51 pm   #7
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Default Re: Whistling Roberts R200

Quote:
Originally Posted by Tim
D.C.C =Dubilier capacitor co.
If these are the little grey ones with rounded ends, these often go faulty too.
I change these as a matter of course too. Some of the later Dubilers were found in 60's and 70's tellys, and weren't much better.
I Well done for finding the fault. Sometimes the old 'scope comes in handy!!
My R200 had loads of dodgy-looking caps, but the real culprit was an innocent looking brownie connecting the aerial coils to TR1 base. With no voltage across it, the little pig was pretending to be a 150 ohm resistor and causing whistling and rubbish sensitivity . You never can tell. Steve.
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