Part 10: Adding the 3 way power switch

I finally got round to fitting the rotary switch mod given in this article on Ampmakers site:

3 way switch mod

The only place really for the switch is on the front panel. I would have preferred to have it rear mounted, but there isnt really a place for it. The diagrams make it obvious.

The front panel seen from the inside - plenty of room and a hole already in place!

Looking at the rear panel on the inside - no space for the rotary switch. Only other option would be further along beside the valve sockets, but that would have meant extending high AC voltage past the valves. Something tells me that would not be good for noise. Besides, its best, IMO if all the mains and hi voltage AC stuff is in the one place.

I wired the switch up and tested it all with a meter before drilling the plexi panel to install it. Note - the chassis has got holes in the right place for this, so it is just the plexi that needs to be drilled. However, and be really careful with this, despite my best efforts, I managed to split the plexi. So I will need to order up another one from Ampmaker. It is almost certainly best to try to make the hole when the panel is OUT of the amp, probably on a flat surface.

Anyway, despite that the rotary switch installed Ok and after the connections were all soldered I tested it, firstly on the bench without the valves, just to make sure the voltages were OK. After that the whole lot got put back together and tested properly.

Rotary switch in position with wires to diodes (brown and white) and wires from power trasnformer (white, yellow and blue)

Note - this is one seriously loud amplifier. Even at 2 watts it is loud. I normally run it through my attenuator to tame it a bit, although I believe that there is a bit of sound quality loss when using this approach. The alternative is to have the neighbours howling at my door....

The chickenhead knob on the rotary switch at the front left side. Note split in plexi (flash from camera makes it less obvious :-) Left position is 2 Watts. Middle position is 9 Watts. Right position is 18 Watts.

Could do with some way of indicating this on the plexi - in a more primitive age , the Dymo tape would have been applied. Maybe just keep it anonymous....

\m/ \m/ Bye for now!

Pics here: