Hi Richard, sorry to dig up this old issue, I assume the amp is long gone now. I use a UK voltage 800RB and sometimes a US model 400RB (same era) with a 2KW step down, I love both amps; they've caused me to fall off the valve amp bandwagon after 2 decades, a long, long story!
I'd just like to know how this saga resolved...the aforementioned repair emporium gave me some advice about an early '70s SVT I used to have and it was, er, a little wide of the mark, and also OTT. My usual repair bloke fixed it very easily, can't praise him highly enough. I'm not saying that to discredit them, to be fair it was over the phone.
My 400RB likewise only has the 2 tabs and is earthed to the chassis. I'd be grateful for any help on this, up to now I'd been blissfully ignorant but resenting lugging a heavy stepdown around! Cheers, Martin.