Magnatone M10a blowing fuses after cap job

[davohilts]

Hello,
I'm working on a Magnatone M10a which was working but had a very very bad hum. The amp came from Ebay and so I opened her up and found it full of disintegrated foam from around reverb tank and inside the speaker cabinet. The M10A is a closed back design and the foam had turned to dust. I cleaned out the old foam and dust and ordered caps which consisted of a 25mf 50volt, 2-1mf 100v, 100mf 100v, and for the filter caps I replaced the old cap can with new axial caps (2-40mf 500v and 3-33mf 450v). I did this after trying unsuccessfully to reform the caps using a variac.
My problem is after I reassembled everything and plugged the amp into a current limiter I built using a 100watt light bulb, the bulb glows bright. I confirmed my fears by plugging into an outlet and throwing the switch and the fuse blows.
I've rechecked my work and don't see any issued with my cap job but I must have messed up somewhere. The amp has the amplifier section on the bottom and the preamp above with a bundle of wires connecting the two. I will attach a schematic and am wondering how I might go about trouble shooting my repair work.
Thanks for any help.

[Jazz P Bass]

Basic troubleshooting.
You have the schematic. That is good.
Unfortunately a schematic is NOT a board layout.
So, you have some homework to do.
Seeing that work was done & now it blows fuses.
With the amp OFF & caps dischargered & all tubes removed.
Get the schematic & verify with an ohm meter, that every point is true.
The polarity of electrolytic capacitors must be observed.
Use your meter & measure certain points to chassis ground.
It all should make sense compared to the schematic.
If you find something that does not make sense, there is the culprit.
Whether it is a crossed solderpath, incorrect orientation of a component or simply a failed component, the static meter test may show the problem.
If all is well, you can power up the amp less tubes.
Measure the B+ Vdc & the heater Vac.
Put in the preamp tubes first.
If the fuse holds & the voltages look good, put in the power tubes one at a time.
Fun, isn't it?

[davohilts]

thanks for the direction Jass! I will follow your lead and see how things come together. The amp is difficult to service because of the two compartments and separate chassis. I will go back over my work when I have a clear head and see if I can find my mistake as I am sure I mis-wired or reversed a electrolytic cap somewhere.

[riz]

If your bulb limiter was glowing, why'd you plug it into the wall anyway? Kind of defeats the whole purpose, eh? Jazz covered it, but yeah triple check polarity of the new caps. And do some searching on the forum for troubleshooting with a limiter, there's been some really good posts about technique, in more detail.

[davohilts]

I know plugging the amp in was classic! Like poking the aluminum dome of a JBL because it has a slight dent in it and making it even worse! I sat down this morning and started with the power transformer chassis because that was the one I did the most work on by changing from a 40 40 30 30 cap can to radial caps tied with zip ties. I checked my work and found no issues with the caps but then I noticed that i had not tied the positive end of the negative voltage cap (100mf 50 v) to ground but to the diode lug next to it. Switched it over one lug and now all is well. I'll check out the posts on troubleshooting with a limiter as I am sure I will run up against this sometime on an amp I haven't messed up on my own.
Thanks!

[1ampman]

If posible take a few pics before disassemble. Point to point wiring can get confusing. Some projects are straight forward others are not..... Glad your all set.

[jrfrond]

Fun to work on those, huh? Weird with the plastic cab and two-part assembly, but they are uber-cool when they work.

The last one of those I worked on had a partial short on the death cap on S1B. I converted it to 3-wire grounded and removed the death cap. I'm not saying that this is your issue, but it might be, and hopefully, your chassis isn't hot! :O

[riz]

+1 on keeping a digital camera on the bench!! One of my best tools!