CHASSIS BASHING

Having decided to carry on with my WS 18 project after the evaluation I now need a suitable power supply, I now know what's required and I will need a chassis to build it on, I will be using quite a big transformer and choke so it will have to be fairly sturdy, the transformer is a bit big for the job but they are VERY expensive to buy and this one has come from my junk box :) Now a word about Chassis Bashing, anyone that enjoys playing with vintage valve / tube technology will sooner or later  have to become acquainted with this gentle art, most valve projects will need a chassis, you can buy one of course but they are usually the wrong size or shape for what you need, better to make one if you can and it is real fun. The one I am about to make is a general purpose Power Supply type, you can see below I have drawn on the Aluminium the basic shape, and have cut it out roughly with a pair of tin snips,

Next below I have put some angle irons in the jaws of my workmate with the rough edge slightly above the flat edges of the irons and tighten up, this also straightens any bends that have occurred during the snipping.

Next I file all the edges with a course file this makes a nice neat straight edges, below

And now comes the "Bashing" part, the folding lines are placed between the angle irons and the whole edge is bent over, to get a nice clean square edge a piece of wood is placed over the bend and you give it a good bash, see below

If the bench is to big for the following bends you can set the next folding lines by using the angle irons placed in the jaws of a pair of welders grips as below, it is more difficult to "Bash"  after you make the bend as you have to hold the grips, but you can use a rubber hammer, it works quite well don't use a metal hammer as it will mark the soft Aluminium.

The ends of the chassis can be bent by just using the Welders grips on their own without any angle irons, below you can see how much I paid for the grips, they are quite cheap :)))

And here is the chassis completed, it is really tough as it is, it won't bend under the weight of the transformer and won't need any riveting or support even though it is only 18swg the standard gauge for a valve chassis.

It is now time to assemble the parts on the chassis and mark where all the sockets and fixing holes will need to be drilled

And here below is the Chassis Bashers dream, a set of hole cutters, anyone like me that has grown up making radio chassis of one sort or another really appreciate the time and effort these cutters can save you, the only alternative is a lot of drilling filing and cursing, I will need to fit an octal socket and the panel fuse neon light and mains switch, all of which can be cut in seconds with these cutters, and here sad to say I feel rather guilty as these cutters are not mine, they belong to a very dear friend of mine, Nigel G4JYU who has very kindly loaned them to me, and so far has been to much of a gentleman to demand their return, but return them I must in the very near future.

And here below is the completed chassis ready drilled to take all the component parts

Here is the end view where the mains lead, mains indicator, panel fuse and on/off switch are mounted

And above the Power supply now ready to be dusted and wired up

And above is the PSU basic wiring complete except for the various supply lines to the octal socket, basically it is three separate circuits, an HT circuit, this now has about 140v AC into a full wave bridge rectifier, with a heavy smoothing choke and substantial smoothing caps on either side this is also loaded with a large wattage resister of about 5k in value, this loads the power supply and tends to stabilise it at about 160v, so there is little change in voltage as the transmitter is keyed and goes from transmit to receive, I could separate the HT supply to the Transmitter MO and further stabilise it which would almost certainly cure most of the chirps on keying, but I'm trying to keep everything as simple as possible for the moment. the other two LT circuits 12v negative bias and 3v heaters use modern low voltage regulators to do the job I suppose I should mention here that I'm using MAINS 240AC to power this PSU and it has 160v DC HT both of which can give a nasty shock or can be lethal. I have grown up with these voltages and so I'm very used to working with them, but if someone reading this decides to have a go and isn't used to working with high voltages then do be VERY careful, or better still just don't do it. Anyway I can now power both the transmitter and receiver units from the one power source, next thing to be done is to make the replacement BFO for the receiver, and start cleaning up the wiring. So BFO and Wiring

G3YUH