28-07-2016, 09:00 AM
(20-07-2016, 01:55 PM)boater sam Wrote: We had a monster as an applications lab item at Ferranti in the late 60's. The output was too high to risk using speakers so it was run into electric fire elements - it boiled kettles.
The output transistors got hot too, we used to spit on them to see if they were up to temperature.
Can't remember too much about it but I know the power supply was off 3 phase mains @440v.
New member here.
Ferranti's Gem Mill had 3 or 4 valve amps in the cellar powering vibration tables for testing semiconductors. They were driven by audio oscillators varying in frequency. The tables had effectively speaker motors mounted underneath. The amps were not Ferranti's build they were called "Kilowatt Star" and were 6ft rack mounted . I managed to buy one of these amps from the scrap heap- it cost me 50p (the standard price for any item found there) and got it home in my Hillman Imp van, the amp weighed about 1/4 of a ton. Some details of the amp , I remember - the HT transformer was 3000v at 700mA, the rectifiers were mercury vapour and OP valve drivers were EL37. I never dared to power it up, it was too scary! Eventually, I sold it for a fiver, so a good profit margin. I should have kept the EL37s though.
Around 1970, Ferranti published a book " Transistor HI FI amplifiers " , designs were developed in Gem Mill application lab and used transistors in the ZT range, e.g. ZT3055. When I started at Gem, there was still some valve production on the ground floor- the equipment for this looked Victorian ( it wasn't!) what with gas jets and vacuum pumps , also there was a lot of Russian 807s tested for some contract, many of these were rejected , they were very poorly made.
While all this ancient valve stuff was going on , we upstairs were assembling huge quantities of very modern (then) TTL and later on , microprocessors,ULAs and ZN414 radio chips.
Bill
