JTM45 Build with issues

Get support and show off your MetroAmp JTM 45 kit builds.

Moderator: VelvetGeorge

Tone_Chaser
Senior Member
Posts: 202
Joined: Sat Nov 24, 2007 2:55 am

Re: JTM45 Build with issues

Post by Tone_Chaser » Sun Nov 16, 2014 3:39 pm

Thanks guys. Yes, the jumpers are underneath and I did that and did the jumpers that way because of the instructions. My '68 was done as you suggested and I did consider it but just decided to follow the instructions.

I will start with the dark room method and see if there is anything going on that way and then proceed checking components with the chopstick method and see if I can find anything that way.
Barry

http://www.flickr.com/photos/tonechaser/" onclick="window.open(this.href);return false;
http://swiftkik.com" onclick="window.open(this.href);return false;
http://lyin-eyes.com/" onclick="window.open(this.href);return false;

Tone_Chaser
Senior Member
Posts: 202
Joined: Sat Nov 24, 2007 2:55 am

Re: JTM45 Build with issues

Post by Tone_Chaser » Fri Nov 21, 2014 1:05 am

I had a little time today to work on the amp again today. I used the chop stick and found the spot that was causing the crackle noise and got it to stop. So I plugged in my guitar and..... no sound. So I kept going and found another bad spot. Now I have sound but it's very quiet. I dimed the amp and it's about as loud as it would be on 1.

So there are at least two bad solder joints that I will try to get to tomorrow. The turrets were full and I had good solder joints until I put the jumpers on the bottom of the board. Lesson learned! I will never do that again. My plan is to go back over the board and make sure all of the solder joints are good again and go from there. Wish me luck! :thumbsup:
Barry

http://www.flickr.com/photos/tonechaser/" onclick="window.open(this.href);return false;
http://swiftkik.com" onclick="window.open(this.href);return false;
http://lyin-eyes.com/" onclick="window.open(this.href);return false;

User avatar
neikeel
Senior Member
Posts: 7231
Joined: Tue Dec 06, 2005 8:31 am
Location: Suffolk, England

Re: JTM45 Build with issues

Post by neikeel » Fri Nov 21, 2014 11:13 am

Tone_Chaser wrote:I had a little time today to work on the amp again today. I used the chop stick and found the spot that was causing the crackle noise and got it to stop. So I plugged in my guitar and..... no sound. So I kept going and found another bad spot. Now I have sound but it's very quiet. I dimed the amp and it's about as loud as it would be on 1.

So there are at least two bad solder joints that I will try to get to tomorrow. The turrets were full and I had good solder joints until I put the jumpers on the bottom of the board. Lesson learned! I will never do that again. My plan is to go back over the board and make sure all of the solder joints are good again and go from there. Wish me luck! :thumbsup:
Good luck.

Suggest only put jumpers under the board if you make the stripped wire long and run it through so you hook it over the turret.

Now check the old 470R vs 470k in the pi (between the 1M resistors) :wink: )
Neil

Tone_Chaser
Senior Member
Posts: 202
Joined: Sat Nov 24, 2007 2:55 am

Re: JTM45 Build with issues

Post by Tone_Chaser » Sat Nov 22, 2014 12:57 am

Thanks Neil. I double checked the 470 ohm resistor and at least that's one mistake I didn't make! :)

Got all of the possible bad solders fixed and no popping at all but the volume issue is still there. I do have a probe that I made to trace the signal through the amp but it isn't here right now so it looks like I'm sidelined a bit until Monday.

Maybe I can get some work done on the cabinet tomorrow anyway. :thumbsup:
Barry

http://www.flickr.com/photos/tonechaser/" onclick="window.open(this.href);return false;
http://swiftkik.com" onclick="window.open(this.href);return false;
http://lyin-eyes.com/" onclick="window.open(this.href);return false;

Tone_Chaser
Senior Member
Posts: 202
Joined: Sat Nov 24, 2007 2:55 am

Re: JTM45 Build with issues

Post by Tone_Chaser » Wed Feb 04, 2015 4:40 pm

Well, life keeps getting in the way and I am just now able to get back to trouble shooting the amp. I started over with the testing part 1 to see where things go wrong.

My voltage coming into the amp is good and my heater voltages are 3.33VAC but it seems like my voltages usually run a little higher than the voltage chart shows, no big deal there.

Next I put in the rectifier and had about 366V on the standby switch and -48V or -49V on pin 5 of V4 & V5.

Now for the preamp tubes. This is where things are going way wrong. The instructions say that the voltages should run about 10% high without the power tubes. My voltages are as follows:
V1 - 1)144 3)1.14 6)146 8)1.14 - all are well below where they should be
V2 - 1)13 3) .56 6) 121 7)13 8)11 - again, all are very low
V3 - 1)236 3)40 6)224 8)40 - pins 1 and 6 look okay but the others a still pretty low and as I was checking voltages, sometimes 3 & 8 of V3 would be around 40V and sometimes around 400V .

All this to say that something is very wrong here!

Right now I believe that whatever is wrong is being caused by the component on top and wiring on the bottom layout I used. I'm going to move all of the wires that make external connections to the top side of the board and see if re-terminating them that way will fix the issue. If that does, it will really be a pretty easy fix. Do you think I should try and move the jumpers to the top as well or see if I can get away with leaving them underneath?

Also, since my band is off for about a month and a half due to one of the guys having surgery, I can get my 100W Plexi out of the trailer in necessary to use as a guide for voltages on the board. If you think that might be a help, let me know. I don't think the voltages would be much different for the most part, would they?
Barry

http://www.flickr.com/photos/tonechaser/" onclick="window.open(this.href);return false;
http://swiftkik.com" onclick="window.open(this.href);return false;
http://lyin-eyes.com/" onclick="window.open(this.href);return false;

User avatar
neikeel
Senior Member
Posts: 7231
Joined: Tue Dec 06, 2005 8:31 am
Location: Suffolk, England

Re: JTM45 Build with issues

Post by neikeel » Wed Feb 04, 2015 5:19 pm

S something is puling down voltages after the PI, or a poor connection in the B+ line after the PI.

What are the voltages along the B+ line from rectifier, screens, either side of the 8k2 dropper and the mid board 10k dropper and on the 16uF board filter cap?

Pics next :wink:
Neil

Tone_Chaser
Senior Member
Posts: 202
Joined: Sat Nov 24, 2007 2:55 am

Re: JTM45 Build with issues

Post by Tone_Chaser » Wed Feb 04, 2015 11:14 pm

Thanks Neil. I've read a lot of threads here and you are always trying to help others and are really great about sharing your knowledge. I really appreciate it as I'm sure all of the others you have helped do as well.

I was doing some testing at lunch today and left my load there so I won't be able to get those voltages until tomorrow.

Is there anything specific that you would like to see, picture wise? I have posted pics on page 1 of the thread but if you want to see anything a little closer or from another angle, let me know and I'll shoot those and post them as well.

Thanks again!
Barry

http://www.flickr.com/photos/tonechaser/" onclick="window.open(this.href);return false;
http://swiftkik.com" onclick="window.open(this.href);return false;
http://lyin-eyes.com/" onclick="window.open(this.href);return false;

User avatar
neikeel
Senior Member
Posts: 7231
Joined: Tue Dec 06, 2005 8:31 am
Location: Suffolk, England

Re: JTM45 Build with issues

Post by neikeel » Thu Feb 05, 2015 4:23 am

Tone_Chaser wrote:Thanks Neil. I've read a lot of threads here and you are always trying to help others
I try, but I am an amateur.
Tone_Chaser wrote: Is there anything specific that you would like to see, picture wise? I have posted pics on page 1 of the thread but if you want to see anything a little closer or from another angle, let me know and I'll shoot those and post them as well.
The pics you posted were during?
A lot of the turrets seem empty of solder and a bit like another thread I cannot see the ground wire to the board filter cap
I have seen the underboard jumpers goint to the wrong connection when the 10k dropper and the cap are transposed.
Neil

Tone_Chaser
Senior Member
Posts: 202
Joined: Sat Nov 24, 2007 2:55 am

Re: JTM45 Build with issues

Post by Tone_Chaser » Thu Feb 05, 2015 4:18 pm

Okay. I had a little time at lunch so I have the voltages.

"What are the voltages along the B+ line from rectifier" – 490V
Screens – 486V
Either side of the 8k2 dropper – 490V to 352V
Mid board 10k dropper – 352V to 211V
16uF board filter cap – 211V

The pics I posted before were from November. I haven't done anything major since then except I did add solder to the turrets since it looks like I lost some when adding the wires to the bottom of the turrets. They're all good now but who knows, that could have caused a bad connection underneath. I still think I will re-run the wires. I think it will just be better for long term stability.

I will shoot the other, more current, pics tonight and get them posted.

Thank you!
Barry

http://www.flickr.com/photos/tonechaser/" onclick="window.open(this.href);return false;
http://swiftkik.com" onclick="window.open(this.href);return false;
http://lyin-eyes.com/" onclick="window.open(this.href);return false;

Tone_Chaser
Senior Member
Posts: 202
Joined: Sat Nov 24, 2007 2:55 am

Re: JTM45 Build with issues

Post by Tone_Chaser » Thu Feb 05, 2015 5:42 pm

I decided to go ahead and remove the wires and start locating them on the top side. I got the borad out and decided I would leave the bus wires on the bottom. I tested the connections and had good continuity on all but one. The jumper that goes between the two lugs on either side of the bias resistors had a bad connection. Everything is good now on the bus jumpers.

This evening I will complete wiring the board back to the chassis components and see where that gets me.
Barry

http://www.flickr.com/photos/tonechaser/" onclick="window.open(this.href);return false;
http://swiftkik.com" onclick="window.open(this.href);return false;
http://lyin-eyes.com/" onclick="window.open(this.href);return false;

Tone_Chaser
Senior Member
Posts: 202
Joined: Sat Nov 24, 2007 2:55 am

Re: JTM45 Build with issues

Post by Tone_Chaser » Sat Mar 07, 2015 11:39 pm

Been a while since I've been back - I moved the wires to the top and the screaming came back. Neil had it right from the beginning. With the primaries swapped, it went away.

I still can't get anything out of it with the KT66 tubes but it works great with the 6L6 tubes. One of the KT66 tubes has a couple of small pieces of glass loose inside it. They also don't quite fit right because they're too close to the OT so I need to move it a little.

Thank you guys for all the help.
Barry

http://www.flickr.com/photos/tonechaser/" onclick="window.open(this.href);return false;
http://swiftkik.com" onclick="window.open(this.href);return false;
http://lyin-eyes.com/" onclick="window.open(this.href);return false;

Post Reply