PRRI no power no light

menamestom

Amp died yesterday, just cut out mid song and then no power.  Assume it was tube related and has taken out a fuse.  So just need to fault find.
I’m thinking the checking / likelihood order is:-

fuses
rectifier
power valves
PT

The rectifier has been in there since I got the amp in around 2010 so that’s my first assumption,  does that sound like the likely culprit?

On a side note switched over to my HX stomp an plugged into the PA and that worked well.  Justified my purchase as well. 

RiftAmps

If it's not a valve that's popped the fuse, the usual suspect on these is the primary side of the PT.

menamestom

RiftAmps said:

If it's not a valve that's popped the fuse, the usual suspect on these is the primary side of the PT.

Fuse is okay, but I still suspect the PT.
It was very hot.  Assume still most likely needs a mew PT?

RiftAmps

menamestom said:

RiftAmps said:

If it's not a valve that's popped the fuse, the usual suspect on these is the primary side of the PT.

Fuse is okay, but I still suspect the PT.
It was very hot.  Assume still most likely needs a mew PT?

So the fuse didn't blow? That points to something upstream of it, mainly the power cable itself.

If the PT is at fault, it'd need replacing.

menamestom

RiftAmps said:

menamestom said:

RiftAmps said:

If it's not a valve that's popped the fuse, the usual suspect on these is the primary side of the PT.

Fuse is okay, but I still suspect the PT.
It was very hot.  Assume still most likely needs a mew PT?

So the fuse didn't blow? That points to something upstream of it, mainly the power cable itself.

If the PT is at fault, it'd need replacing.

I tried a different kettle lead but that made no difference.   I’ll give it another check.

PT wise, if it does need replacing, is there a preferable replacement other than Fender?
It’s not done bad, hundreds of gigs over 10 years but if there’s a more reliable, direct replacement may as well go for that?

DJH83004

If it turns out to be the power transformer, then my suggestion would be to fit a Hammond replacement (Canadian) or TAD, both offer direct replacements. You really need to get the chassis out and start checking the wiring and also the DC resistance of the primary winding.  

RiftAmps

Just had a quick look at the schematic and forgot that these have two internal fuses (F2 and F3, both 7A), check those and report back

menamestom

RiftAmps said:

Just had a quick look at the schematic and forgot that these have two internal fuses (F2 and F3, both 7A), check those and report back

Thanks, will do.  Didn’t see any fuses when I had a quick look at the chassis, but being a bank holiday, kids and family around so have suspended checks for now, will have a good look tomorrow.  Cheers

menamestom

menamestom said:

RiftAmps said:

Just had a quick look at the schematic and forgot that these have two internal fuses (F2 and F3, both 7A), check those and report back

Thanks, will do.  Didn’t see any fuses when I had a quick look at the chassis, but being a bank holiday, kids and family around so have suspended checks for now, will have a good look tomorrow.  Cheers

Ah, I wasn’t looking for soldered in component type fuses.  Both look okay, and measure 0 ohms when measured in the circuit.  Have taken the valves out but am wondering whether i’d need to fake the board out and lift one leg?

DJH83004

RiftAmps said:

Just had a quick look at the schematic and forgot that these have two internal fuses (F2 and F3, both 7A), check those and report back

That's a good point as the indicator lamp is fed off the heater supply via fuse F2. There is also a Thermistor after the mains on/off switch and main fuse feeding the primary winding which could also be suspect.