Okay, so I'm no expert on amp building. Let's just have that out of the way to begin with. I've managed a couple of successful builds, but am very much on a learning curve every time I even look at an amp.

That having been said, I wanted to share some photos because they're the sort of thing I was looking for and couldn't find anywhere a few days ago. What they show is the before and after states of some wires where a change of lead dress fixed a problem with my amp.

I'm not suggesting that what they show is a magic fix for a specific problem or anything like that. All this is intended to do is describe a problem, describe the process of isolating it and describe what the solution turned out to be.

Again, let me emphasize that I'm a beginner with little experience, and don't fancy myself to be any sort of amp guru. And as such, though my process did involve looking at the layout and schematic for the amp to try to zero in on where the problem might lie, for the most part it was like trying to get better reception with your TV antenna, you know; move it a little this way or that way and see what happens.

Okay. So my 6A20 sounded pretty good. I thought I'd done a build that had zero problems. Yeah, a little hiss, a tiny bit of hum when it was cranked up on both channels, but nothing to speak of. Pretty darn proud of myself, I was....

Then about a month after I got it up and running I was fooling with it and found a problem. Maybe I just hadn't set the knobs right when I first tested it out, or maybe some components changed values after burning in for a while. I don't really know whether anything changed or whether I just missed it. It was an easy problem to miss - the amp had to be set in a way that I would probably pretty much never do.... Anyway, here's what was happening:

With reverb and vibrato turned on and everything on the vibe channel turned up to 10 but the bass turned to 0 the amp sounded like a helecopter. I guess this is called "motorboating". Turn the bass up a bit, it would go away. Turn the vibe down a bit, it would go away. Everything at 10, no prob. Turn the treble to 0, it's back. Everything at 10, no prob. Turn the vibe intensity down a bit, at about 7 it would come back a little.

I really didn't want this problem - I wanted to have done a perfect build and not have to troubleshoot because I had no idea how to even begin. I had no idea about how to diagnose it and I was afraid that in the process I'd make things worse instead of better. And, hey, how often am I going to run the amp with Treble or Bass at 0 and everything else at 10 (Verb, Vibe Speed and Vibe Instnsity included)? Geez, maybe I should just leave it be.

But there it was. Putt-putt-putt-putt-putt-putt-putt-putt.........

So I pulled the chassis out and found a chopstick and started poking and prodding around. I started with the leads going from the board to the pots: If you look at my lead dress in this photo you'll see that they were all just loose, not bundled or anything, and my best guess was that my problem was somewhere there. I set the amp up with the chassis open on a table, the speaker hooked up, the reverb tank hooked up, with the reverb and vibe pedal's switches connected and set to "on", powered the amp up with the knobs set to make it do the motorboat thing and started prodding the leads going from the board to the pots to see if I could make the motorboat sound change or go away.

I started having some success, but it was like "whack a mole". Every time I thought I had it solved a new set of settings on the front panel would bring it back. Like, if I pressed a lead from the reverb pot against the lead to the treble pot in one certain place it would go away, but then if I turned the treble to 0 and the bass to full it would be back. Or, I'd get it all gone, but then turning the normal channel to 10 would bring it back. Or, I'd get it gone and then turning the 'Verb to 6 would bring it back. Different tone each time, but same problem popping up at different settings.

Each time I thought I had it solved I would power down, discharge, and make wraps of wire around the leads where it made the problem go away, fire it back up, and find the problem at a new setting. I had wraps binding the Vibe channel tone pot leads to the reverb pot leads, holding the vibrato pot leads against each other in a particular way, and one wrap that pressed one lead from the vibe intensity pot against a B+ lead to the bias board in a particular place.

Each itteration of this process changed the motorboating sound, solved it for one set of settings but as said, each time I would find a new set of control settings that brought it back.

So....

I started poking around elsewhere. I poked at resistors and caps on the board to see if I got crackles. I poked at the wires coming off the RCA jacks on the back of the chassis. And then I started poking around the leads from the main board to the tube sockets. All of this was done with the amp set to make the motorboat sound, so I got to listen to it putt-putt-putting for a good hour or so.

Where I hit paydirt was poking around the leads to from the main board to V5. On my build, there's a B+ wire that comes up from the doghouse to supply power to the vibrato bug neon bulb, and the wires to the tube socket cross paths with it. Moving the B+ wire and the wires to pins 1,2 & 3 on V5 made the motorboating change. A little push here, a little bend there, lift the B+ wire a little higher, move that pin 1 wire away from that pin 2 lead a little, louder, softer, different tone, louder, then suddenly GONE.

Here are a couple photos:

Before... (click for bigger)

After the first fix (click for bigger)

So....

I poked around some more. I found that with all the knobs at 10 I could poke leads around and occasionally cause the amp to give a little more hum or a little less hum, so I went around poking at everything trying to find the "less" side of any hum I might be hearing change with any given poke. And I did the same with my leads to the pots.

And I did the same with every resistor and capacitor on the board. Not bending everything all out of whack, mind you, just a little push to see if anything changed, a little touch or tap with the stick to see if the stick's proximity caused any spurious noise. Most of the time, no effect - once in a while, a little something. Push those coupling caps apart a little and it gets a tiny bit quieter; move those tube leads close together - hum - push them away from each other - less - let's go with less...

All of this made my board look a little less neat and tidy, but the amp was a bit quieter, and hey, my motorboating problem was gone.

Feeling pretty proud of myself, I buttoned the amp back up and took it upstairs for a test drive. And indeed, it sounded fine, no motorboating at any settings and the "Normal" channel sounded ... hey, a LOT better.... But I wasn't sure about the "Vibe" channel's tone. It seemed a little mushy. And after all, I'd done some odd twistings of leads to make that motorboating go away before I found the problem at the tube leads and those twistings were still in place....

So....

The next day I opened it back up and undid the oddball twistings. Especially the one with the B+ wire to the bias board being pressed against the Vibe intensity pot lead. And I redressed these twistings in what seemed to be a more "conventional" manner, gathering the tone leads for the Vibe channel together, and the vibe and verb leads together.

This isn't the prettiest thing you'll ever see. (Wanna' see beautiful lead dress? Go here: B.Hill Amplification)

But, hey, I said I'm no expert. Anyway....

Powered it back up, and... Putt-putt-putt-putt-putt...........

Having zeroed in on the leads going to the right side of V5 and their relationship with the B+ wire to the verb bug, though, I messed with them some more, poking them and prodding them into different positions. And after about a minute the motorboat sound was gone again.

After the second fix (click for bigger)

Just like fiddling with a TV antenna.

This time when I buttoned it back up and played it both channels sounded good. As a matter of fact, I think they sound great. They sound a LOT better, in fact, than they did before I worked on this problem with the motorboating. Tighter, with a little KE-RANG when you really pop the strings. Nice reverb. Nice Vibe. ...Okay, when you turn the Vibe up all the way, and the treble up all the way there's a quite little hiss-hiss-hiss-hiss, but that seems to be expected and I can live with it. For today, we'll chalk it up as a win and get back to playing guitar.

Thing is, as much as I dreaded the process at first, dealing with my motorboating problem led to me learning how to make the amp sound a lot better. If it hadn't been for the amp having this fault I wouldn't have had to get up the nerve to go poking it with a stick, I wouldn't have learned how to do this, and my amp wouldn't sound as good as it does now. Heck, I'm gonna' crack my 5E3 open and do some poking around, who knows, maybe there's some room for improvment in there....