h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I've just bought rebuilt BBC Monoblocks. Aparently they date from the late 50's and used a Mullard circuit - the 5-20 - 5 valves, 20 watts, maybe made by Mullard for the BBC. They (now) have 2 Siemans EL34's, and EF86 and ECC83. The rectifier is Mullard GZ34. All silver wired and driven by ancient Ferranti pure iron transformers, the only original parts. A plaque on the end says "BBC AM8 -4A".

Does anyone know anything about them and their history. They may have had a triangular chassis and according to one website, and were used in studios for mastering purposes

John Chapman

Hi John, Sorry for the delay in answering, but I'm not on h2g2 much these days.

These sound like a worthwhile acquisition. I suppose they would be good for around 15-20 watts, but the frequency response might not be up to modern standards. Even now the Beeb builds their speakers to have a 40Hz - 15kHz bandwidth, and these amps are from the 50s, possibly before even FM radio, so they would be quite conservatively spec-ed. But frequency response isn't everything, and if they sound good today, that's what counts.

If the original chassis was triangular they were probably built for a peculiar speaker to today's eyes which was a corner-mounted baffle only with the single driver in the middle. I think they might have been used for engineering area monitoring, the studios having something a bit more rigorous. They would probably have been used singly as they pre-date stereo. You could call it "mastering" if you like, but the term hadn't been invented then, so that's probably dignifying them a bit!

Tell me how they sound in a modern set-up, and I'll see if I can get any further info on them.

Doug.