JTM45 Reissue Board kit instalation

[passerby3141]

Hello all, doing my first real amp work with a Metro Amp JTM45 board replacement in my 45 RI, and have hit a bit of a snag.

There are some things I am finding a bit confusing with my installation of this board. First, how to hook up the big can dual caps. The wiring diagram that came with the kit doesn't seem to explain how to hook up both positive leads, there only seems to be one lead labeled coming of the board for each cap on either side of the large 10k resistor just before the biasing section of the board.

Also, I do know a little tiny bit about electronic wiring from redoing the wiring in my strat. It seems a lot of the initial differences between stock and the wiring diagram that came with the kit have to do with the ground leads. Rather than redoing all of that I am seriously considering using my before mod photos to base my work off of. Comparing the original board wiring with the PTP kit, shows only one difference, the buss lead from the 10k resistor to the 27k resistor at the bottom of the board is not duplicated on the PCB circuit board.

Can I just wire up the new board exactly like the old board? I actually de-soldered every lead, so I have all the original cables to work with. Or are the dual caps wired differently in the circuit because of the different values?

Any comments would be appreciated, and in spite of the bit of frustration, I am actually having lots of fun with this project!

-Adam

[passerby3141]

Ok, I haven't completely figured it out yet, but I think I have guessed part of what is confusing me.

This amp has obviously been modded at some point, I bought it used. It had Philips orange caps in it, that is one sign. I think someone replaced the dual filter caps at some point then, put the originals back in, but backwards. The lead colors may have been reversed off of one positive terminal.

I understand that I am not using any of the proper terminology when describing what I am seeing in the amp, so I should really bone up on that to communicate better.

Also I have found that I was wrong about the PCB board, it has the exact same layout electronically as the replacement board. Need to take my time!

[thousandshirts]

Hi Adam

Have you got a digital camera? Even with a cell phone camera, you can take a bit of a picture of what you're looking at, and kind of point out in writing what is giving you pause. Post the pic and a little explanation if you ever get stuck, especially with the parts on the PTP board versus the PCB.

Did you find the board component names graphic?

It isn't the same for each amp - some have slightly different component values - but
by in large if you get familiar with it, you will really know your way around much better.
The PCB won't look exactly the same, but the PCB does the same function, so it will be
similar. Hopefully this will be a bit of help:

[passerby3141]

That's brilliant. I think I am slowly getting my head around it. The thing that was really throwing me for a loop was connecting the dual filter caps. I think when whoever put the amp back together before I got to it, they didn't seem to care which dual cap was doing what, as they are the same value in the stock reissue. So, some if the wiring was a little bit hairy. I have been going through the Metro JTM45 instructions to follow the wiring there as well as the other material. I will get back here again if I hit a wall.

[thousandshirts]

Good stuff. That's what we're here for. If nobody writes back in the first day, just be patient or give your thread a little bump. Someone will be with you shortly.

[passerby3141]

Ok, I have a question! Thanks for the interest by the way thousandshirts.

In the JTM45 wiring guide that came on my cd-rom, the choke and 32uf cap are attached to a 10K resistor just before the bias section of the board, on the tube side. On the other end of this 10K resistor is one side of the dual 16uf cap. At the same point where the 32uf cap and choke are soldered, the board buss wire runs across the board, eventually ending at another 10K resistor, on the pots side of the board.

On the tube side of this same resistor is the other side of the dual 16uf cap.

doesn't this connection put two 10K resistors between the two positive ends of the dual 16uf cap? The schematics that came with the kit clearly show only one 10K resistor between them.

Or am I missing something?

I noticed that in this write-up of the Metro JTM45 board kit, that the author had wired things according to the Metro wiring diagram,
http://www.legendarytones.com/metroamp.html" onclick="window.open(this.href);return false;
This of course makes me doubt myself, but in my photo of my pre-my-moded version of my amp, all the connections on the 10K resistor near the bias section are clearly reverse the wiring diagram that came with the kit. In a word......

confused?

Also, on the wiring diagram, there is no actual mention of where the other half of the dual 16uf is supposed to be attached or that the sixth pin of the power amp sockets are also attached at the point where the 32uf and choke are attached.

So, if anyone could tell me if I'm missing something I would appreciate it.

[passerby3141]

After careful study of the schematic and forum searches. I think I have every thing connected. It seems some of the wiring diagrams are wrong and or incomplete and it is well documented.

But damn does this thing sound great! Far and away the best amp I have ever owned or possibly even played!

After sorting out the dual cap connections, I found some other differences among the diagrams. In the JTM45 RI replacement board, a 220uf cap is used as the cathode cap, but in the Metro 45 instructions a 330uf is used. I tried both but settled on the 220uf. Also, I noticed that in the BB circuit a 100uf cap is used on the volume 1 pot, so I switched to that since I will be playing through a 2x12 for now. All seems well, quiet operation, and the amp seems much louder now.

Very, very pleased!

Now to read about iron, but some speakers should really be my next move.

[thousandshirts]

All right! Glad to hear that the amp is sounding good and running proper.