Dyanco problem
bk wrote:
Thanks for all the assistance so far. Ill give an update as to what
has been done so far.
I rechecked all the bias on the power tubes and all check out fine.
.40 volts which is what they should be(this is a VTA board, its fair to
say its a rebuild of the stock circuit). I checked the voltage on pin
1 of the first PreAmp tube and it was around 450 volts which is about
300 volts HIGHER than its supposed to be. I got a bit scared and
turned the amp off. heres a few other things ive done:
did the chopstick test on anything i could find but nothing
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.
thanks fora the assistance.
What is the URL for the schematic you have used for this amp?
Have you followed it carefully?
One must be able to service anything one does diy, and asking
why you have no music at this NG here is not always going to be helpful
although you will get at least several overlapping sources of advice.
But without the EXACT schematic you have in front of us
how do we know what could be wrong?
We need to be able to talk about the circuit in front of you.
The 450V at the anode of V1 won't cause any damage BTW, and there was
nothing to fear.
What was the 0V rail voltage with respect to the chassis?
But you didn't then measure the dc current in the anode supply
resistors,
or cathode resistors and probably you have not grounded something
as you should have so no Ia flows in the RL or the tube, so the anode
voltage is
up at the supply voltage.
It would seem you are fairly untrained in the basics; I was there once,
but
you should be asking 101 questions about voltages and currents in ALL
the R components around the circuit
as you prod places with the voltmeter knowing exactly where you are on
the schematic.
be careful measuring around the circuit because a shock from 450V can be
a real bother.
As you prod and calculate current using ohm's law with your calculator
you should record the
voltages on a copy of the schematic, printed up nice and big, or
carefully
written out in front of you, which BTW teaches you to concentrate where
every part is
and familiarize yourself with the parts.
Never assume anything you've done is correct until you've proven it to
be correct, so assume
until the proof is in that you have probably made at least a few
mistakes.
The man who makes no mistakes makes nothing, usually; we all make them,
so don't be afraid.
Patrick Turner.
|