well the bridge rectifier checks out ok.  It might take a few days to get a current limiter rigged up.  I'm in a dorm room so i need to scrounge some tools and materials. anything else i can try in the meantime?

1) Red to TIP142 tab=1081
2) Black to TIP142 tab=655
3) Red to TIP147 tab=723
4) Black to TIP147 tab=kept counting until it read infinite
and now
5) Red to TIP142 tab, black to TIP147 tab=kept counting to infinity
6) Red to TIP147 tab, black to TIP142 tab=1223

7)well the rectifier diodes are not individual diodes, it is a rectifier chip.  i checked the zeners just after the filter caps in case that would tell us anything.
one read close to 800 with black to strip, and infinity the other way, the other diode read 640 and 840 respectively on the same measurements.

i looked up the data sheet for the rectifier.  Its rated for 6 amps.  that sounds a little low to be running at full power for a few hours.  Is there a way to test this rectifier as if it were individual diodes?

oh, and what exactly was i measuring there?  I like to know what i'm actually doing.

Even with the screws removed and the transistors pulled up so that they are not touching the heatsink, i still read continuity from the tabs to the sink.  Could they be shorted through something else nearby? 

I didn't remove them, i tested for shorts while they were in the circuit.  I guess that probable wasn't an accurate test.  However, i did a continuity check from the metal tab to the heat sink.  Both had continuity, despite still having the spacer under them.  Could this have been from over heating when they failed?

On that note, was overheating probably what caused them to fail?  There's a pretty weak heat sink on the transistors, so i want to try and make sure this amp is gig ready and won't just fry itself again.

I'd love to post the schematic but i had to get it directly from crate.  I had to sign a waiver agreeing not to post it anywhere before they would give it to me.  I can't find one online anywhere.

Now i'm a little confused.  The schematic shows the two red leads from the transformer secondary going to the rectifier, but these are at 56 volts.  The schematic is a combined drawing for the 65 and 120 watt versions of this amp.  The third green wire is a center tap.  Should i be using one red lead and the center tap going to the rectifier?  Thats the only way i see to get the voltages low enough to have 40 volt rails and not 80.  then should the third wire, the unused red one, be grounded where the center tap used to be?

My friend brought me this amp in a few pieces.  He had tried to diagnose the problem himself, and he didn't pay attention to where the leads were originally.

i checked the voltages on the output transistors.  I measured from the mounting tab, which should be at ground, to each leg.  For the tip142 the voltage for every leg were between 78 and 83 volts, and on the 147, the two outer legs were both around 80 and the center leg was at 0.  What does this tell me?

I also used the audible continuity test on my DMM.  With one lead attached to the grounded mounting tab, there was continuity between all three legs of both transistors.   As far as i can tell, they're both blown. 

You mean test the Voltages on the transistors with no speaker attached?  I want to make sure i understand correctly.  And how exactly do i test the transistors?  Remove them from the circuit and use plug it into the sockets on the multimeter?  I'm used to dealing with tubes, so i don't know how to test most of this stuff.

Hey guys. A buddy of mine asked me for help trying to repair or at least diagnose the cause of his xt65 dying.  Its not actually dead, per se, as it still makes some noise.  But the noise it makes is only a loud buzz, and the guitar signal cannot be heard. 

This all started hen he played a gig and had the thing at max volume for an hour or two.  He said smoke started coming out of it and its been worthless ever since.  I hooked it up to a test speaker to measure the transformer voltages under load to see if the transformer itself was the problem.  as soon as i turned it on, the cone on the speaker moved forward as far as it could, and began to smell like it was burning after only a few seconds. Obviously something is placing a high DC potential on the speaker. 

So i have two questions

1. What could cause DC on the speaker like that?
2. Is it safe to test a transformer with just the primaries connected, and measure the voltages at the secondary side?