Hammond M3 to 5E3 conversion

[Pdavis68]

I've got the parts for the Bandmaster/Concert on order. They'll be in this week.

So yesterday I had nothing to do and decided to start cleaning out the M3 chassis. Removed components from the chassis and the two board. Washed the board down in acetone and then rubbing alcohol. I removed solder from the sockets I'm going to reuse (2 octals, 2 novals. I left the rectifier and heater wiring in place, 'cause... "Done!").

So then I decide I'll go ahead and start populating one of the boards for the 5E3, with whatever components I had on hand. I had completely forgotten about a bunch of .1uf polyester caps I had on hand. So next thing you know, the board was done...

I need to put rip out one of the strips of terminal connectors on the front (already removed 2 others) and then I need to put a metal plate along the front and rivet it into place, to cover the holes left by the terminal strips. When I'll drill out the holes for everything.

Turns out the only components I didn't have on hand to complete the build are filter caps, a power switch (not doing a standby switch) and a power indicator lamp...

So this thing is going to be done in no time...

You'll notice I didn't leave room on the board for the filter caps. There are some terminal strips on the inside of the chassis that are well placed for them, so I'm going to put them there instead.

[Pdavis68]

I got all the parts for my Bandmaster build and I detoured on that for a few days, but I'm going to go ahead and finish the 5E3 build first. My reasoning being that I care more about the Bandmaster and I'm still at the stage where every amp is significantly better than the one before it. So I should practice more on the 5E3, then do the Bandmaster...

So without further ado... I cut out some sheets of metal and riveted them to the front of the chassis to cover where the terminal boards were. It created a lot of headaches for drilling holes (not a problem with the next build as it's a pre-drilled chassis!!!!)

After doing that, I got the holes drilled out. I tore up one of my little metal sheets in front drilling holes, so I had to drill out the rivets, cut a new sheet, drill it, blah blah blah... Accidentally broke the plastic fitting that held one of the big caps, so I had to yank that out, cut a sheet to cover the whole it left, drill and then rivet it in... Used a wire brush drill bit to scrape off some rust spots. Tedium... Not the part I like doing...

Got everything drilled out for input jacks, speaker jack, power switch, pots, fuse. So I'm all set to go... I'll have to drill a hole to screw in a terminal strip, but I'm not 100% sure where I want that yet. I'll drill it when I figure that out.

So I should move forward quickly on this, now that the slow, boring stuff is done... I've decided I'm going to add Rob Robinette's Fixed Bias/Cathode Bias switch mod. I want to play with fixed bias and I have to drop 60V off the PT anyway, so I'm going to use a string of 5x 12V 5W zeners to create a -60V tap off the CT of the PT secondary and then I'll add a voltage divider with a pot for it. Now the fun stuff. I'm excited...