Finally Building JTM45: Stupid Questions As They Arise

[Phil_S]

Can't see for sure, but I'd make sure any wire doesn't have contact with those sandblocks. They get very hot.

[The New Steve H]

Man, I'm glad you pointed that out.

[The New Steve H]

Man, jamming those capacitors in there isn't much fun. The clamps do not fit the chassis. Next time someone brings me a Mojo kit, I'll tell him to build it himself.

[The New Steve H]

I'm finishing up the wiring on the JTM45. I've noticed that some people recommend 20 gauge or bigger on the power amp, but Mojo sends 22 gauge wire with the kit.

I have been replacing the cloth 22 gauge with Teflon 22 gauge from Apex Jr. Do I need to take out the 22 gauge in the areas where there will be relatively high current? Seems to me that Mojo wouldn't send 22 gauge if it wouldn't do the job.

I did put heavier stuff on the ground wires from the power supply capacitors.

[ToneMerc]

I'm finishing up the wiring on the JTM45. I've noticed that some people recommend 20 gauge or bigger on the power amp, but Mojo sends 22 gauge wire with the kit.

I have been replacing the cloth 22 gauge with Teflon 22 gauge from Apex Jr. Do I need to take out the 22 gauge in the areas where there will be relatively high current? Seems to me that Mojo wouldn't send 22 gauge if it wouldn't do the job.

I did put heavier stuff on the ground wires from the power supply capacitors.

22AWG is fine.

TM

[The New Steve H]

Thanks.

Today I realized why other people's amps look neater than mine. They only use one or two colors of wire. I like to mix it up so I can tell things apart.

[Structo]

Well there used to be sort of a standard for leads to the sockets.

Like red plates, blue grids, yellow cathodes.

That may be all wrong but you know what I'm saying.

[Jana]

blue is plates, green is grids.

[ToneMerc]

Here's reference for you yung fellas

http://www.regiscoyne.com/tech/trannyCC/

TM

[Structo]

Thanks, I know it's not followed that closely anymore but it would be nice if everybody used the same code.

It's funny that even Leo Fender didn't really follow the codes in his amps.
Frequently using green for heaters and yellow for just about everything else.

[The New Steve H]

A code would be smart, but if no one follows it, it's not much of a code.

Even using random colors makes the amp easier to fix.

I want to get this thing finished so I can try my low-watt Bassman idea.

[The New Steve H]

I got the amp wired up. I put it on the current limiter and gave it a whirl. It turned out a few connections had been overlooked. The heaters worked, but the "on" light went out after I turned the standby switch off, and the heaters dimmed. The light on the current limiter brightened, leading me to wonder if there was a short.

I fixed everything I could find. Now the "on" light flickers, and I hear a rattly sort of sound in sync with the flickering. This only happens when I come off standby. I haven't heard a thing through the speaker yet.

I haven't biased the amp yet. I assume that is not the problem; correct me if I'm wrong. I thought it would be okay to get it running before fine-tuning it.

I used the Mojo layout, which I don't like a whole lot. There is a wire from pin 8 of the rectifier, straight to the standby switch. On the other side of the switch, there is another wire from one of the big caps, plus a wire from the choke and the center tap from the OT.

On the Ceriatone layout, it looks like the choke and OT go right to the cap.

This amp has Classictone transformers, as noted above. The wire colors are different, but I have checked and rechecked everything, and I can't find anything I've done wrong.

I'm not too happy with the Mojo experience. Tonight I turned my homemade Bassman over to use it as a guide. I had remembered it as a big mess, but I was wrong. It's actually WAY neater than the Mojo kit.

I think I'm going to move the wires to the cap. I see no reason to clog up the standby switch and run long wires across the chassis.

[The New Steve H]

Well, I figured it out. I may have an IQ of 57, but on my home world, I am considered a genius.

1. The Mojo layout appears to suggest grounding out the speaker jacks. I guess I don't understand their symbols. Anyway, undoing that bit of magic helped a lot.

2. I had the wires from the OT reversed. I knew there was a pretty good chance they were screwed up, but I planned on fixing it later. I didn't know it would totally disable the amp. It laid a big square wave over everything past V2, and it sucked the life out of the PT.

I just tried the amp out with my amazing Chinese Epiphone Riviera with Lollar P90s. It sounds very good, but frankly, I would not put it up against my 5F6A. If it was my amp, I'd stick Svetlana 6L6s in it with a 12AY7. But then I'd have two amps that sound exactly the same. I'm sure it will please the friend I built it for.

Of course, I have no idea what it sounds like when properly biased, so I could be totally wrong.

[The New Steve H]

I know no one will get overly excited about completing a kit amp, but I'm putting up a picture anyway because I'm so relieved.

I really cannot recommend the Mojo chassis. I guess other people have said this already, but I am repeating it. It's tight, and some of the holes are a little off, and it DOES NOT LIKE KT66s. If I hadn't had my own milling machine, this would have been a horror to fix.

[Reeltarded]

No way! Good job! That amp threw a bunch of curves at you and you bent it straight!

Some assembly required, I'd say.