The WEM copicat still causes amazement to all those who use, see or work on one. Physically moving parts clearly make a difference to the human ability to understand. Almost anyone that watches the little tape spin around the can see and imagine this marvellous device works with just a quick explanation and a bit of experimentation you gets it like that.
Being mechanical as well as electronic and old brings it’s own set of maintenance challenges. Worn motors, dirty or magnetised tape heads, distorted transport panel leading to misaligned heads. There are also some fragile components inside that form part of the bias oscillator that need to be carefully examined for any minor damage as any slight movement can lead to unpleasant distortion of the audio signal. The valve circuit itself is not particularly unusual and the usual suspects like cathode decoupling and interstate coupling capacitors as well as drifting carbon composition resistors are all worthy of checking and replacement.
Recently I was lucky enough to get some great help on a Mark II copicat from John Beer of Amp fix otherwise known as doctor copicat. John is concentrating on building some beautiful Dominator amps and so referred the case over to me since it was a Bristol musician. The unit had been damaged in transit and the motor completely jammed – it’s a good idea to always pack the motor with some bubble wrap or similar during shipping to prevent this kind of damage. Once it was moving again there were a few minor components to replace to get the unit back to reliable working order.