Metro JTM 45 build Start up questions

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

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vh junkie
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Re: Metro JTM 45 build Start up questions

Post by vh junkie » Sat Jun 06, 2015 11:42 am

Triple check that the OT wires are what you think they are. Did ****** give you a diagram for the OT?
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danman
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Re: Metro JTM 45 build Start up questions

Post by danman » Sat Jun 06, 2015 12:32 pm

VH Junkie raises a good point...definitely check the OT wiring diagram again for confirmation before trying the 6L6's.

kadswan
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Re: Metro JTM 45 build Start up questions

Post by kadswan » Sat Jun 06, 2015 4:26 pm

Image
Here is the photo, of the power tranny wired up with the orange high voltage wires, and cleaned up. I got rid of the terminal strip.
These are my voltage readings after switching to transformer wires
V1 pin1 206v, pin3 1.8v, pin6 204v, pin8 1.7
V2 pin1 179v, pin3 1.1v, pin 6 317v, pin8 181v
V3 pin1 239v, pin3 43v, pin6 224v, pin8 43v
V4 pin3 435v, pin4 434v, pin5 -47v, pin6 434v
V5 same as V4
recto pin2 435v, pin4 326, pin6 326, pin8 435v
I'm gonna try some 6L6s just to see if it is the tubes. Any other suggestions of what to look for. Thanks again in advance

kadswan
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Re: Metro JTM 45 build Start up questions

Post by kadswan » Sat Jun 06, 2015 4:31 pm

He did send me an email with the wiring diagram. On the primary, brown is the center tap B+, black goes to V5 and red goes to V4. On the secondary, yellow was chassis ground, green 8ohms, blue 16ohms, and white was 100 volt line, which I cut and covered. There was no 4ohm tap.

kadswan
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Re: Metro JTM 45 build Start up questions

Post by kadswan » Sun Jun 07, 2015 10:30 am

I haven't tried the new tubes yet. I was reading some posts of similar problems with startup, and decided to try putting in one power tube at a time. I used one tube in both sockets, just to make sure I didn't have a bad tube socket as well. With one tube in, there was a very slight hum through the speaker load, but it did not blow the fuse. I checked my voltages and they all dropped very close into range. I figured with both tubes they would come into range right on. I did this with both tubes, and got the same result. I then put in both power tubes, hit standbye, and the loud hum and motor boating were back. I turned the amp off before it could blow the HT fuse. I'm at a lose. :bang:

vh junkie
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Re: Metro JTM 45 build Start up questions

Post by vh junkie » Sun Jun 07, 2015 10:41 am

Have any pics of your under-board wiring is the jumper between the pot side of the NFB resistor and the PI tail (10k) there?
Are you sure the orange and green wires are not reversed under the board?
Try it with one end of the NFB resistor lifted.
"With all due respect, sir, you're beginning to bore the hell out of me."
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kadswan
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Re: Metro JTM 45 build Start up questions

Post by kadswan » Sun Jun 07, 2015 3:15 pm

I will check all that tonight and post my findings. Again, thanks for all the help

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Re: Metro JTM 45 build Start up questions

Post by kadswan » Mon Jun 08, 2015 5:17 pm

I pulled the board just to make sure all of my jumpers were in place, and in the right spots. They all looked good. I had the board out so I just went ahead and rewired it just to make sure I didn't have any frayed wires or cold solder joints. While I had the board out I changed the grounding bus, to the Larry/Star grounding system. Wired it back in, and now I'm getting 328v on pin 1 of V1. That can't be right!!! I didn't bother putting in the power tubes of course. I don't know where to go from here. Should I remove the 10K resistor on the pot side, and check voltages again? Could a bad resistor be causing this? I'm ready to launch this thing in the lake and see if it floats.

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Re: Metro JTM 45 build Start up questions

Post by danman » Mon Jun 08, 2015 5:43 pm

So you are now seeing 328vdc at pin 1 v1? Is this with preamp tubes installed or without? Did you also check voltages on v2 and v3? If you lost your B+ feed to v2 or v3 that may explain why you are now seeing such high voltages at v1. You can check for B+ on the turret board where it first comes in at the 10k dropping resistor (located to the right of the nfb resistor). From there just follow your jumpers to each 10k decoupling resistor all the way down to V1. Check for DC voltage all the way down the line and at each tube socket. I know this can be frustrating in a new build but at least you will learn quite a bit about troubleshooting the circuit.

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Re: Metro JTM 45 build Start up questions

Post by kadswan » Mon Jun 08, 2015 6:56 pm

I did check V2 and V3, with the preamp tubes in. The voltages are slighty higher, but not significantly. I'm getting around 328v on the 10K resistor on the tube side 378v on the pot side, and 329v on the positive side of the 16uf cap.

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neikeel
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Re: Metro JTM 45 build Start up questions

Post by neikeel » Tue Jun 09, 2015 10:32 am

What are your heater voltages now? - they were 7vac which is still high even allowing for drop with tubes in

What is your wall voltage?

Check your choke and screens wiring as some of the board links are for using the turret nearest the output sockets as choke and sceens hook up and others that turret is PI coupler.

Did you take a pic of your underboard wiring?

Must confess I am getting lost follwing all the different revisions pictures :stars:
Neil

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Re: Metro JTM 45 build Start up questions

Post by kadswan » Tue Jun 09, 2015 11:54 am

Neikeel.
Thanks and I'm sorry for all the revisions. You're really gonna hate me cause I rewired the board, and used different color wire cause I ran out of green and yellow hook up wire. I am going to remove the board and take some very clear photos of the underside of the board, and the chassis without the board installed. I will not do anymore major overhauls, and just stick to trouble shooting with ya''lls help. I will get the pics up asap, and again thanks to danman, Neikeel, and VH Junkie for all of your kind help so far. :toast:

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Re: Metro JTM 45 build Start up questions

Post by kadswan » Tue Jun 09, 2015 1:21 pm

Here are the new pics of the board front and back. Chassis without the board installed. I ran out of wire, so the yellow wires are now gray, and the green wires are now orange. Let me know what you all think.
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neikeel
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Re: Metro JTM 45 build Start up questions

Post by neikeel » Tue Jun 09, 2015 2:30 pm

Ok, so the blue wire going off the board in the top pic (from the link wire that feeds the PI plates) goes to the PI filter cap and the 8k2 resistor on the board will have the yellow screens supply wire greatly shortened and hooked up to it on the terminal closest to the output valve sockets.

The rest should be fine. Be wary of reversed primary wires 9oscillation and banshee scream if the green/orange wires go to wrong socket!)

Post back when you have done. I am not familiar with the Classic Tone PTs but they do seem to give quite high voltages!
Neil

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Re: Metro JTM 45 build Start up questions

Post by kadswan » Tue Jun 09, 2015 2:56 pm

Here is a better pic of the underside of the board.
Image

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