Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Tapsnap on February 21, 2019, 05:31:43 pm
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Now, that I have my single ended amp working well, (thanks everyone for your help) my attention has turned to the other amp I have been working on. It’s a simple 6V6 push-pull amp with a 12AX7 preamp tube and a 12AX7 paraphase inverter with a volume and a gain.
Building this thing was a frustrating pain from the start, mainly because I built it in a chassis that was way too small. The chassis was way too small because I was trying to fit it into a cabinet that was also way too small. Despite the never ending problems of one thing getting in the way of another, and neither my fingers nor my soldering iron being able to reach the things that I needed to get to, I finally got it finished. It worked well …….except for this annoying little hiss and hum when I turned up the gain.
So I started trouble shooting the easy stuff, to get rid of the noise. No success. So then I was faced with the reality that I would have to take this thing apart again. Ahhhhhggg!!!
After several days of ruminating about it, I thought, to hell with this I’m just going to start again in a bigger chassis and then make a bigger cabinet.
So, I thought I would show you the progress of my new amp.
I started with a piece of steel I got from my neighbor. It's rather thick measuring 1/8" but I'm not too bothered about the extra weight. Bending it, of course, takes a few extra steps. I don't have a 50 ton press so I will need to grind the fold lines.
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This is a shot of what will be the inside of the chassis. As you can see I have cut a "V" groove at all the fold lines. The groove depth is about half the thickness of the steel plate. In effect, I will be bending 1/16" not 1/8" metal. I like this thickness in part, because tapped screw threads will be more secure and will less likely strip.
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I've drilled most of the holes before bending. There are a few that will be drilled after. By the way, the chassis will end up being 17"x 5"x 3" The piece of steel I started with was 24" x 12"
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I like watching stuff like this.
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How did you cut the V groove?
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Willabe, I cut the grooves with an angle grinder. First with a cut-off wheel, to get the depth quickly, and then with a regular worn grinding wheel. I take off the handle and use the holes for the handle to bolt a piece of angle iron to it. I can then run that along a fence that I clamp to the sheet of metal. I came up with this a number of years ago when I used to make sculpture.
Here are pictures of the bends. I have to work on the fitting of the edges a little before I weld the thing up tomorrow.
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After some grinding and some filing, I was able to get the edges to miter together properly, so I welded it together, making sure all was square. I then sanded the control panel surface on the belt sander.
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I haven’t posted to this thread for some time, nevertheless I’ve continued to work on this amp slowly. So here’s an update.
I’ve made the pine cabinet and I’m getting ready to stuff the chassis with the circuit board and make final connections.
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Looks awesome! Can’t wait to see more.
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+1 awesome !!!
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GREAT STUFF!
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Love your perseverance! Bravo!
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So here’s the chassis all together. I plugged it in and I’m getting the same hiss and hum when I turn up the gain pot. It’s the pot mounted on the underside of the chassis. The wires going to it probably need to be shielded, so I’ll be changing those next. If that doesn’t work I’ll probably get rid of it and put in a fixed resistor.