Metro JTM 45 build Start up questions
Moderator: VelvetGeorge
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Re: Metro JTM 45 build Start up questions
OK. I think I'm getting somewhere. My voltages are back to where they were with the power tubes not installed. All seem to be just about 10% over. I fired it up again with the power tubes, and got a fairly loud hum, but then a intermittent thump, not the motor boating I was getting before. I know I have the green and orange wires from the board going to V4 and V5 pin 5 they way the instructions have it, but could these be reversed and be what is causing my problem? I was also thinking of reversing the output primaries going to the power tubes, but isn't that usually a loud squeal that happens when those are not in the correct order? Any thoughts. I think I'm making some progress.
- neikeel
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Re: Metro JTM 45 build Start up questions
Good.
The way to check if you have reversed primaries is to simply unsolder one leg of the NFB resistor from the turret leave it mid air and retest.
If that is the case you need to swap the primaries, put the NFB R back and retest.
BTW regarding the pop, do you have 5k6 swamp resistors between the orange/green grid wires and the sockets and if you can find one a 1000v rated 0.05uF cap (600v will do) between the B+ out from the rectifier and ground helps (solder to the socket with insulation on that lead and the other end to ground).
The way to check if you have reversed primaries is to simply unsolder one leg of the NFB resistor from the turret leave it mid air and retest.
If that is the case you need to swap the primaries, put the NFB R back and retest.
BTW regarding the pop, do you have 5k6 swamp resistors between the orange/green grid wires and the sockets and if you can find one a 1000v rated 0.05uF cap (600v will do) between the B+ out from the rectifier and ground helps (solder to the socket with insulation on that lead and the other end to ground).
Neil
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Re: Metro JTM 45 build Start up questions
Niekeel, I owe you a beer!!!! The first thing I tried before switching anymore wires around was the 5K6 swamp resistors, and voila, no hum no motor boating, no thump and the amp works great!!! I biased the tubes around 45ma and plugged in and played. I want to thank everyone for the kind help getting this beast going. I have learned a lot so I think this was a great experience in troubleshooting. Now I want to start tweeking. Just can't put the soldering iron away. Thanks again to Danman, VH Junkie and Niekeel. You all rock!!!!!
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Re: Metro JTM 45 build Start up questions
Happy to hear that you got it sorted out! Good call Neikeel!
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Re: Metro JTM 45 build Start up questions
Hi, u can get tubular 0.005uf/1000V caps at www.justradios.com. They do have a minimum order of $20 tho, but have a lot of items u may be interested in (including NOS I believe). They also have resistors that are properly voltage rated for tube applications. Hope this helps. Cheers
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Re: Metro JTM 45 build Start up questions
Thanks Ivan. good to know
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Re: Metro JTM 45 build Start up questions
Actually, I just checked their site, it appears they don't have NOS, sorry, but they do have a wide variety of quality components. Cheers
- neikeel
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Re: Metro JTM 45 build Start up questions
That is good because I like a beer now and againkadswan wrote:Neikeel, I owe you a beer!!!!
Neil