bk wrote
found that sound is actually comming out of both sides. when i fire
the amp up it stats up as normal and the music starts to come up for
roughly 2 seconds (as the tubes warm) it than reaches a peak and
instantly dies. the whole process lasts about 2 seconds.
I had a replacement choke i decided to try to replace since the old
one
was leaking wax however that did nothing. havent swapped out the
tubes
however they were working fine before i started. Another thing to
note is that if i do turn the amp up full volume I can faintly hear
music however it sounds crunchy.
Ive checked values of alomost all the resistors and everything
checks
ok. - not fully completed but will be shortly. all wire
connections
seem fine and ive gone over the solder connections and removed any
excess blobs which may have occurred and resoldered most
connections.
I also put in a new rectifier tube and ive removed and installed all
brand new ceramic tube sockets. exact same problem as initally.
seems
anything i do produces origional results. once again this was a
fully
functional amp, everything worked until i put this new board in.
dont
have the original board anymore so cant test.
The high anode voltage means there is no or hardly any current to that
anode. Possibilities: the valve is at fault; the cathode resistor has
failed open or otherwise doesn't connect the cathode to ground; the
grid leak resistor likewise; the grid stopper resistor likewise.
A circuit for your amp (schematics index), and information on valve
pinouts (data sheet locator), can be found via
http://www.duncanamps.com/
The grid stopper is the one connected to the grid. The grid leak is
between the other end of the stopper and ground. No stoppers for the
input valves in the original, looking at the schemo, and the leaks
aren't obvious...the 470k Rs just after the input jack. A link to the
circuit for your driver board would be useful. The diagram I'm looking
at (
http://www.curcioaudio.com/st7_mnl.pdf) doesn't show a ground
connection at all, ahem. Should point "D 9" be grounded? Anybody?
Possibly your ground isn't, either. If by "both sides" you mean both
channels, rather than both PP phases, then prime suspect is the
connection between both cathode resistors and ground, for the valve
with the high anode voltage, and presumably its mate in the other
channel.
If it wasn't going to be OK, it would have got worse by now.
cheers, Ian