I have owned a Selmer amp for many years now and finally found the time to give it a full service and overhaul. I saved this amp from going in the skip, as no one knew what it was and assumed it was rubbish. To start the project I printed a schematic and traced the circuit from some resources on the web. http://www.vintagehofner.co.uk/ is a great resource for old British Amplifiers.
The next step was to photograph the chassis and make a note of the connections and colour coding used. Although I deviated from this in places of the restoration, the wire I used to replace the amp was far superior.
I set about removing all the existing wiring and restoring it to new safety standards for practical use in the studio and for live gigs. One area of major safety concern was the HT resistors which were just attached directly to the mains transformer and handing about 420V which read up on the Fluke multimeter and AVO.
I had the option of keeping the Original components and using NOS components to keep it in its original state,however decided to make it a reliable and serviceable amp rather than a vintage collectors piece. No metal-work modifications were made however, so the amp can be fully restored back to original or period components if necessary.
And After - Sleeved Around the HT and Mains fuses and HT rectifier diods attached to a tag board which is mounted to the bolt for one of the HT Filter electrolytic capacitors.
Also the wiring is grouped using sleeves for extra safety and noise free operation.
Chassis looked like this after removal. Not sure what the 60 indicates. Number 60, Made in 1960 ? could be a chassis manufacturer code. Either way it is left on, despite pencil graphite being conductive. Luckily it is well under the main circuit board.
Unsolder the circuit board after hand selecting the correct values resistors. A very hot and powerful solder gun does this quickly and efficiently with minimal stress to the components. Instagram photo, because I am a hipster.
Heater wire in white for the valves. Twisted by hand in places but also wound using a hand drill for speed. Everything is nice and sleeved and kept at minimum length to prevent losses in the signal. Resistors also replaced with the correct values of high-voltage type in appropriate places.
And here is how it sounds. All controls were half way on the normal channel using the Low input. Very clean and noise free indeed.
This will now get used at band practice, gigs and in the studio.
The original British made Mullard and Pinnacle valves were tested on a AVO and came up good. They glow well and are very noise free with low microphony.
My next project is to build a Audio power attenuator to allow the amp to be driven hard at a manageable volume that wont cause complaints in residential areas!