Roberts R300 being restored...

[Nick]

Hi

I've just received an immaculate Roberts R300 complete with original paperwork & receipts etc. from 1965. It's missing the central tuning knob - cream with a brass inset...

Anyone got a spare? Pretty please?

Also, has anyone restored one of these? What to look for, apart from the usual caps etc. The AFnnn transistors I know can get tin whiskers, so how to deal with those (if they are there)?

Thanks

[boater sam]

I think Roberts may have knobs. I make my own brass inserts.
AFxxx and most Mullard canned transistors have tin whiskers. They can be blown away on the ones with a screen with a charged capacitor once removed from the set. I believe that there are some of other makes that do not have the problem.
Simply cutting the screen can effect a temporary cure.
Just giving them a hard rap often does the same, for a while. Buying new ones is pointless as any old stock will have the same problems.
It is possible to replace them with modern silicon transistors, often without changing the bias resistors.

[Mike Watterson]

Replace AF117s etc if faulty. Not all go bad. Probably excess tin plating, I've used AF12x and also Russian Germanium. Sometimes even PNP silicon without re-biasing on IF stages with emitter resistors. It may have been even one production plant.