Magnatone M15 - Ground Wiring

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Re: Magnatone M15 - Ground Wiring

Postby vez on Wed Dec 10, 2014 2:58 am

LongerDelay,
Looking at the schem atic I realized I gave you a bum steer.
The electrolytic caps in the -17 volts line will have the "+" side going to ground because ground is more positive than -17.
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Re: Magnatone M15 - Ground Wiring

Postby jaywalker on Fri Dec 12, 2014 3:52 pm

It's ok (and a good idea) to exceed the voltage rating on those 450v caps. See if you can find them with a 500v rating. Wall voltages have gone up over the years since this amp was built.
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Re: Magnatone M15 - Ground Wiring

Postby dragonworks on Sun Jun 14, 2015 4:21 pm

I bought one of these, non working, have found this thread very informative. I rebuilt the power supply and put a three prong plug in but it seems I will have to read this all through again and get it right. Just starting out at this. I put all new tubes in. The amp is now working at I would think regular volume, but still a lot of noise. The reverb section doesn't work and I bought a new tank for it, still doesn't work, han another tank kicking around, that one doesn't work, so I am guessing the problem is somewhere else. The trem works fine. I haven't had much time with it and it is still "apart". Will get back to it one of these days, to may hours at my "real" job.
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Re: Magnatone M15 - Ground Wiring

Postby jaywalker on Sun Jun 14, 2015 5:58 pm

LongerDelay wrote:PROBLEM: I performed continuity tests from the chassis of the power supply to each of the pins in the harness. Pin #2 made connection as expected (it is wired to the chassis of the power supply from the factory), but also Pin 6 and Pin 10 made connection which I was NOT expecting. When examining the schematic, pins 6 and 10 appear to carry 6.3 volts of AC to power tube heaters in the head. But in the power suppy chassis, they are 2 solid green wires that come out of the transformer and have continuity with each other when testing.[/img]


I'm wondering how the OP made out with this amp. I see no problem with the filament wiring which is unrelated to rewiring the power cord and removing the death cap(s), as far as I can see. There would be continuity between pin 6 and pin 10 (and pin 2 for that matter)....if you look at the heater taps in the PT those are the two ends of the heater coil (solid green wires) and there is also the center tap to ground (also pin 2 tying the two chassis' together ground wise regarding the heaters).

The top chassis has to be tied somehow to the bottom to complete the grounding for your new third prong on the power cord. IIRC , I've had to add a wire connecting top chassis to bottom on an old Gretsch amp.
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Re: Magnatone M15 - Ground Wiring

Postby jaywalker on Sun Jun 14, 2015 6:14 pm

Hi dragonworks. Replacing all electrolyic caps and cleaning connections, pots (sparingly) and preamp tube sockets with Deoxit spray is a good place to start.
Bone up on safety procedures first and foremost.
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Re: Magnatone M15 - Ground Wiring

Postby PeterS on Sun Jun 14, 2015 9:01 pm

still a lot of noise


Hum, hiss, frying, crackling or motorboat? :D

For the reverb, plug everything in as normal, turn up the reverb and bang on the tank. If it makes noise the problem is on the driver side.
No noise, it's the recovery side.
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Re: Magnatone M15 - Ground Wiring

Postby dragonworks on Sun Jun 14, 2015 11:01 pm

It has been quite awhile since I last fooled with it. I cleaned all the pots but not the tube sockets. It wasn't motorboating, hiss and crackle. Before I did the power supply all you got was a loud hum.
After recapping etc she played okay but noisy and no reverb. The original reverb unit had a broken connection where the spring connects to the transducer? I thought I had fixed that by taking a paper clip, bending it just right and soldering it in there and rehooking up the spring, but of course, that was hoping for too much. As I stated, I am just a beginner at this, I have had some success, fixed and old masco amp, mostly by trial and error but learning along the way, fixed a couple of stereo receivers, a peavy classic 30, this power supply, recapped my super reverb power supply. Read a lot, still hard to relate what is on the schematic to what is in the amp but I am getting there. Understand a lot of the theory but none of the practicality. I will be retiring soon from forty years as a machinist and my playing skills are slowly eroding, would be nice to learn this to stay in the business after the hands finally give out.
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Re: Magnatone M15 - Ground Wiring

Postby PeterS on Mon Jun 15, 2015 12:44 am

Do you have ohmmeter? First thing to do with the reverb is check the continuity of the 2 coils (input and output) in the tank.
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Re: Magnatone M15 - Ground Wiring

Postby dragonworks on Mon Jun 15, 2015 4:16 pm

I have an ohm meter but one of the tanks I bought brand new as a replacement tank, and it works in other amps, the other tank I tried also works in other amps.
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