DIY HiWatt problem

[Mr.Curwen]

A while back I built a HiWatt DR103 clone, with a 12AU7 power section (NOS Miniwatt). I was very happy with the sound, it really does the Pink Floyd thing good. Lot's of balls as everyone said.

Of course the sound isn't going to be as big as with EL34's, but to tell the truth I really don't have the money for bigger iron (or for big attenuators to get overdrive), and the 12AU7 option has worked for me very well on several projects, especially with the NOS tubes I was lucky to stumble on to.

Anyway, as a curiosity I recorded a small demo with Fuzz Face:

http://www.youtube.com/watch?v=K4UAuNrscF4

Few days ago, something went wrong with my HiWatt clone. The sound is first alright, just like before, but when I strike a note in the mid to high register, it sustains (it only does this with Fuzz Face, clean notes are ok) for a little while (maybe a second, second and a half) and then just abrubtly dies out. No fading, sudden death. The sound is fine if I play for example arpeggios or whatever where I strike the notes more quickly again - only the sustain is missing.

The Fuzz Face is ok, sustains infinitely on my Plexi clone, so must be the guitar and cables also. The tubes also perform normally on my Plexi. Reflowed all the solder joints.

I will make a recording of the phenomenon tomorrow (as it is 11 PM in Finland as I'm writing this).

Any thoughts?

[Bob-I]

Sounds like a problem I had with an amp a few years ago. Turned out to be a bad connection on the grid load resistor on one of the preamp tubes.

[selloutrr]

test the tubes or swap with a known good tube first

then check for a cold solder point, or failed part...
( only fails under stress ) chop stick it after it's been on
make it fail and try to chop stick it back to life.

[Structo]

Could be a filter cap taking a dump.
So it is running out of reserve before the note decays.

Wild ass guess is what that is, but I had an amp do that before.