First JTM45 build

BashCoder · Post by **BashCoder** » Fri Jan 20, 2006 11:17 am

Day Two -- I took my time on the heater wiring, so it was about two and a half hours for this building session. I installed the bias resistors and the yellow wires, but since I don't have the OT yet, I skipped those connections and the choke.

Here are a few things I've noted so my next build goes smoother. Some of these may sound really dumb and obvious, but here goes:

- I could find no way to fit the two choke wires through a 1/4" hole and grommet, at least not with a Mercury Magnetics choke. I had some larger grommets around, so I drilled that out a bit bigger for an easy fit. This was the very first thing I did as I started to build, and it became my first comical obstacle: 15 minutes installing a grommet, whoohoo!

- Bend the grounding lugs 45 degrees before you install them. Especially when you get to the dual can cap, where it's flush to the chassis, it's a pain to pry up once installed.

- Your screwdriver is going to slip once or twice and you're going to scratch up the top of your chassis. Get over it -- this is a rock and roll amp, not a Corvette. Next time I'm going to put a ceremonial scratch on the top before I start building.

- Don't just follow the instructions, follow the schematic too.

NY Chief · Post by **NY Chief** » Fri Jan 20, 2006 3:52 pm

Funny, I have very similar notes from my (first) JTM45 build!

Billy Batz · Post by **Billy Batz** » Fri Jan 20, 2006 4:15 pm

BashCoder wrote:- I could find no way to fit the two choke wires through a 1/4" hole and grommet, at least not with a Mercury Magnetics choke. I had some larger grommets around, so I drilled that out a bit bigger for an easy fit. This was the very first thing I did as I started to build, and it became my first comical obstacle: 15 minutes installing a grommet, whoohoo!.

Thats funny. Next to heaters mounting the parts on the chassis is annoying. All tge slotted machine screws. Its a pain. I fit all the PT secondaries through one hole before. That was a trip.

- Bend the grounding lugs 45 degrees before you install them. Especially when you get to the dual can cap, where it's flush to the chassis, it's a pain to pry up once installed.

See I prefer to do it the other way. When their bentthey wont stay put. They fall away and off the screw. I just use a tiny screw driver to pry them up then a larger screw driver to push against the point where you bend it so its a nice even bend.

- Your screwdriver is going to slip once or twice and you're going to scratch up the top of your chassis. Get over it -- this is a rock and roll amp, not a Corvette. Next time I'm going to put a ceremonial scratch on the top before I start building.

Those polymer screwdrivers come in handy for some things.

Flames1950 · Post by **Flames1950** » Fri Jan 20, 2006 5:26 pm

Billy Batz wrote:Youd normally twist a long length first then cut smaller lengths and unravel the ends to go to and from the tube sockets.

But even then some wires don't untwist right, they want to stay twisted no matter what....I wish I'd thought of sticking some extra wire ties on there instead of simply swearing and throwing the occasional screwdriver that is unfortunate enough to be nearby when I get ticked........

BashCoder wrote:Your screwdriver is going to slip once or twice and you're going to scratch up the top of your chassis. Get over it -- this is a rock and roll amp, not a Corvette. Next time I'm going to put a ceremonial scratch on the top before I start building.

You think scratching the chassis is bad -- wait until you get to the plexi panels!!! There is no way under God that the strain relief will go in without at least one big scratch across the back.

BashCoder wrote:I could find no way to fit the two choke wires through a 1/4" hole and grommet, at least not with a Mercury Magnetics choke.

Believe it or not, it can be done, I've done it with both Heyboer and MM chokes. The real bitch is that the grommet keeps trying to come out, so you gotta hold it in place while you carefully pull the wires with your other hand. But if you've got the bigger grommet anyway, what the hell......

Billy Batz · Post by **Billy Batz** » Fri Jan 20, 2006 6:28 pm

Flames1950 wrote:But even then some wires don't untwist right, they want to stay twisted no matter what....I wish I'd thought of sticking some extra wire ties on there instead of simply swearing and throwing the occasional screwdriver that is unfortunate enough to be nearby when I get ticked........

C'mon! Just twist each one back the opposite way. You old guys have trouble getting things to be strait.

Flames1950 · Post by **Flames1950** » Fri Jan 20, 2006 8:24 pm

It just depends on the wire. George's standard stuff works OK bending it back. The thinner gauge I got from him for my JTM45/100 was real bitchy about straightening back out.

BashCoder · Post by **BashCoder** » Fri Jan 20, 2006 8:45 pm

Billy Batz wrote:Those polymer screwdrivers come in handy for some things.

No doubt -- I need some badly!

NY Chief wrote:Funny, I have very similar notes from my (first) JTM45 build!

Good to know, Chief -- I don't feel so dumb now

Flames1950 wrote:Believe it or not, it can be done, I've done it with both Heyboer and MM chokes. The real bitch is that the grommet keeps trying to come out, so you gotta hold it in place while you carefully pull the wires with your other hand. But if you've got the bigger grommet anyway, what the hell......

Yeah, that's what kept happening to me too -- grommet kept popping out!

I took the day off today and built all day. Started at 8:30 AM and next thing I knew it was getting dark outside. After 11 hours of huffing solder smoke, I'm a bit wiped out! I must be having fun, because it felt like about 4 hours...

Billy Batz · Post by **Billy Batz** » Fri Jan 20, 2006 9:31 pm

For every push into the hole, you have to come back out a little bit so the elasticity of the lip can set back up along the edge of the hole.

.... Dont even biother with this one Andy. Its too easy....

Flames1950 · Post by **Flames1950** » Fri Jan 20, 2006 10:25 pm

Billy Batz wrote:For every push into the hole, you have to come back out a little bit so the elasticity of the lip can set back up along the edge of the hole.

.... Dont even biother with this one Andy. Its too easy....

Damn, what a setup though........

Flames1950 · Post by **Flames1950** » Fri Jan 20, 2006 10:26 pm

I took the day off today and built all day. Started at 8:30 AM and next thing I knew it was getting dark outside. After 11 hours of huffing solder smoke, I'm a bit wiped out! I must be having fun, because it felt like about 4 hours...

Sucks you right in doesn't it? How many times did I tell myself, just one more wire?

BashCoder · Post by **BashCoder** » Sat Jan 21, 2006 1:09 am

Flames1950 wrote:Sucks you right in doesn't it? How many times did I tell myself, just one more wire?

Sure does! I was saying the same thing to myself tonight. I'll post some more pics in the morning.

Man, building amps is hard work! There's so much tedious handwork that is very time-consuming. It's very fun and totally worth it, but it doesn't come easy. And I'm not having to do any metal fabrication at all.

All that is to say that I now realize what a great value Metro's pre-built amps are. They aren't cheap, but dang -- there are a ton of man-hours invested in each amp and hardly any room for automation or economies of scale.

Much respect to you, George!

Billy Batz · Post by **Billy Batz** » Sat Jan 21, 2006 1:58 am

Abotu a year ago I had two friends at once ask me to do amps for them. I did one for my old sound guy for a mild $400 profit then promptly convinced my buddy that upgrading a RI was the way to go. For me amps have to be a labor of love. If not it can be very frustrating building them. I know a lot of hobby amp builders, especially new guys whove only done one or two, think theyd like to do it for a living but I can see the novelty wearing off real quick. Thats me anyway.

Lets see some pics after 18 hours of progress

BashCoder · Post by **BashCoder** » Sat Jan 21, 2006 12:05 pm

Day Three -- 11 hours-o-fun

Mmmmmm... Maaaaarshally....

Yesterday I mounted and wired all the pots, switches, jacks, fuse, lamp and some of the socket-mounted components. I was also able to get the board wired and half-installed.

WARNING:
These photos contain lead, which the State of California says is dangerous.
The State of California makes an excellent point.
But it also says pot is medicine, so...

I made my first real mistakes today, though not bad ones.

- V2 gets a 100k resistor across two (well, really three) pins. I had the pincount off by one because I had just worked on an octal and for some reason temporarily thought the preamp socket had 8 pins. I had already clipped the leads, and now it doesn't reach. I used another one in the kit and can pick up a replacement at a local shop.

- When I soldered all the wires to the board, I used purple wires instead of five blue ones. I was working off a printout and the color difference wasn't apparent. Not a big deal, but I have seen how pictures posted to this forum has helped folks find and fix problems, so I wanted to make sure it was standard so I fixed them.

- When I wired the board to the preamp sockets, I didn't leave enough slack to easily pull the board out and tilt it up. This is important because when my OT arrives, I want to be able to easily install it. I had the yellow wires to V2 and V3 pretty tight, so I replaced them and a couple others.

The obstacle du jour was on the back plexi faceplate, and was minor. The hole for the impedance selector swtich was too small (the hole in the chassis was fine) I nibbled out some of it with diagonal cutters and finished it off with a Dremel. Then I placed the selector and drilled the two mounting holes through the plexi. Not a big deal, just added some time to the build (and this is why we call it a build and not merely an assembly, after all). Below is a shot of the panel, pre-Dremel:

Lessons learned:

- Buss wire makes bad solder. I mean... not that I accidentally picked some up and tried to solder with it... No.... that would be stupid... I mean, in theory it should make a bad solder because of it's high melting temperature and lack of a rosin core....

- After each build stage, wipe down the inside of the chassis and around parts to clean up rosin residue and bits of solder. It was also helpful to use my 100psi air compressor to clean out small pieces of wire, solder and insulation bits that fall in.

- Also clean up the work area after each build stage. Now that the plexi panels are in place, I don't want to scratch it up because of scraps on the bench.

- Think ahead, read ahead in the directions.

Billy Batz · Post by **Billy Batz** » Sat Jan 21, 2006 1:41 pm

BashCoder wrote: - When I soldered all the wires to the board, I used purple wires instead of five blue ones. I was working off a printout and the color difference wasn't apparent. Not a big deal, but I have seen how pictures posted to this forum has helped folks find and fix problems, so I wanted to make sure it was standard so I fixed them.

I dont know if everyone does this but when I do an amp I usually populate and complete the entire board before it goes in. I put at least 2 more inches to each of the wire lengths then I think Ill need. Thats why I usually get 2 full amp wire kits for one amp. Otherwise it would be cutting it close with 6' of each. If you do the board before going in the chassis theres only a few turrets you have to leave unsoldered for tranny connections. But for connections to pots, jacks, switches and cans/fuse holders I put all the wires on and do the board before it goes in. I just always felt its easier that way. If you put the board in and connect the wire before the components and you intend to put the wires into the turrets from under the board instead of wraping them around the turret, then you have to watch you dont push them out as you try and shove all the other leads in there.

What I do is strip off enough of the wire to be able to bring the bare wire in enough so that I can turn it 90degrees over the top of the turret and hook it on. Then I solder just enough to make it stick to the turret in an out of the way spot. Also when you clip the lead legs of the components make sure you clip them short rnough that they wont go through the bottum of the turret and hit the insulation of the stripped wire. That can be a pain.

The obstacle du jour was on the back plexi faceplate, and was minor. The hole for the impedance selector swtich was too small (the hole in the chassis was fine) I nibbled out some of it with diagonal cutters and finished it off with a Dremel. Then I placed the selector and drilled the two mounting holes through the plexi. Not a big deal, just added some time to the build (and this is why we call it a build and not merely an assembly, after all). Below is a shot of the panel, pre-Dremel:

Hell Ive drilled em with drill bits and step bits. I think those panles are weak to certain kinds of stress but I dont think people need to be paranoid about drilling them. If your holes arent lined up perfectly with the chassis for instance, Id take a drill bit about the same size as the hole and drill it. The metal is hadrer to drill then the plastic by a huge degree so it pushes the drill to ream out the panels overlap.

- Buss wire makes bad solder. I mean... not that I accidentally picked some up and tried to solder with it... No.... that would be stupid... I mean, in theory it should make a bad solder because of it's high melting temperature and lack of a rosin core....

- After each build stage, wipe down the inside of the chassis and around parts to clean up rosin residue and bits of solder. It was also helpful to use my 100psi air compressor to clean out small pieces of wire, solder and insulation bits that fall in.

Thatll do it. I have to use caned air.

- Also clean up the work area after each build stage. Now that the plexi panels are in place, I don't want to scratch it up because of scraps on the bench.

2 minutes of tweaking and somehow my workbench is a shithouse of tools and metal pieces and wire.

BashCoder · Post by **BashCoder** » Sat Jan 21, 2006 2:10 pm

Great stuff, Dan -- thanks.