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Haven't done any electronic projects since the 6G6 Bassman build. It's that time of year where I sit around and vegetate so I decide to do a conversion on a little Champion 600 I bought when they first came out a few years ago. It has always hummed about as loud as the maximum volume on the guitar so it never got used. I didn't want to spend a lot of money on magnetics and wanted to use what I already had on hand. Problem was, all conversion I've seen are done by changing out the magnetics and using a tube rectifier. No schematics or layout diagrams for what I wanted so I set about to design my own diode rectifier layout by searching the internet. Here's where I am at at this point of the project. My problem now is, I have found two different sources on wiring the AC power to switch and fuse. The old Fender layouts show AC going directly to the switch and then to the fuse, others show it going to the fuse first then to the switch. Hopefully someone here can provide the correct answer for safety. These drawings are done by me as an example.







Fabricating the circuit board out of left over Bakelite material fron another project. Will be drilling and installing eyelets

Looks like it will be a cool project. Can't wait to see how it turns out.

As for your questions, the ac primary wiring that you have drawn up is correct. The hot (black wire) from the ac cord goes to the fuse, then to the power switch and then to the power transformer. The neutral (white wire) goes directly to the other end of the transformer primary winding. Officially, the ground (green wire) should be longer than than either the hot or neutral wire and should be attached to ground at it's own chassis point, that is marked with a ground symbol.

I reviewed the rectifier plan, but I'm not sure that it will work as shown. Does the power transformer high voltage secondary have a center tap that is grounded? If it does, then the series diode string will work, if not then you will have to use a rectifier bridge with it's negative side grounded.

With modern day diodes, you really don't need to have 2 or 3 in series. Fender did that back when the diodes were rated for much lower voltages and putting them in series increased the overall voltage ratings.

Thank you Mr. Bill, I was hoping I could count on you.

The transformer does not have a center tap. It is rated at 275V. Regarding the bridge rectifier would the following wiring diagram be what you are referring to or is there more to it than something this simple? According to Fender 5F1 schematics it shows 340V at the first high voltage capacitor. I guessing there is more to it.

That's what you need, the negative end is grounded and the positive side is your main B+. The red ac lines from the transformer go to the two sine marked inputs.

Based on the basic rule of thumb, 275 X 1.4 = 385. You should get about 385 vdc as the main B+.

I flipped the above diagram on my pattern drawing maintaining the proper orientation of the diodes to make a cleaner looking circuit board. I will run the ground wire to the board mounting screw designated as the bullseye circle. If this look right I'll go ahead and drill my circuit board for eyelets. BTW, do I need to add a resistor to drop the voltage from 385 down to the 340 as shown on the schematics or is 385v alright?

The diodes are IN4007

That layout for the rectifiers is perfect. The 600 used the same basic system and it worked fine at 366 vdc, so i'd say go for it.

I just looked at the layout for the filaments, you will either need to add two 100 ohm resistors to create a ground reference or ground one side of the filaments and have the other side at 6 vac. If you don't the amp will hum like crazy.

Mr. Bill wrote:
I just looked at the layout for the filaments, you will either need to add two 100 ohm resistors to create a ground reference or ground one side of the filaments and have the other side at 6 vac. If you don't the amp will hum like crazy.

Will do. I remember you advising me to do that on my 6G6 build as there was no center tap on the transformer. I'm expecting some parts in tomorrow or the next day so I it should go pretty fast once they all arrive.

Well, as luck would have it, I didn't get one of the filter caps in today's shipment so that will set me back a few days. I went ahead and installed all the AC components. Those are some tight quarters near the fuse and pilot light. I soldered the 100 ohm resisters to screw terminal before installation making it a lot easier. The heater wires are not soldered in place but look like it in the photo. At this point could it cause any problems firing it up to check the red leads voltage coming off the transformer?

Man, I'm sorry I have no answers for you, but I just wanna say that I'm impressed and a bit jealous of you guys that can build an amp. It's so cool. Best of luck to you with it.

Thanks Greg! I know just enough to get in over my head into then have to ask Mr. Bill to bail me out. But, it is fun!