Thorn 8500 Chassis
Model: Ferguson 3713
Original List Price : £222.64 (exact price in 1971 unknown, this is the 1975 price )
Integrated Circuits: Yes
June 1971 saw the production of the first British colour chassis aimed at breaking through the £200 barrier – The Thorn 8000 series chassis. With a 17″ A44-271X shadowmask tube and all solid state circuit. Along with its sucssesors the 8000A, 8500 and 8800, proved to be very popular with the viewing public and more reliable than many engineers at first predicted.
Here we have the Ferguson 3713 with the 8500 chassis which was released in July 1972. It differs from the 8000 using a 19″ tube: the higher scan drive requirements led to a redesigned line output stage and focus circuit and the use of a choke instead of a dropper resistor in series with the live mains input line. This latter modification provides an HT rail of about 190V in place of the 170V used in the 8000 series. Line output is via a 1700V transistor the BDX32
Lots of work required on this one as it had been stored in a humid metal shed. The cabinet and stand are OK but the chassis and its components had suffered with rust. It needed many transistors replacing along with IC’s and pre-sets. The CRT is also low emission on the Red gun. I managed to repair it to a reasonable level but colour is poor. There’s enough life to give a good grey-scale. Thankfully a NOS A49 192X has been found so I will get around to replacing the CRT soon. For now some photos of its repair.