Tim Schwartz wrote in message
...
On 1/4/2011 9:27 AM, N_Cook wrote:
Tim wrote in message
...
Hello and Happy New Year all,

I've got a Luxman R117 receiver here that breaks into a wild
oscillation when the amp is pushed. I believe that it occurs when the
amp switches from the low B+ rails to the high B+ rails. Turning up
the
treble control seems to make it worse, but that might be a red herring.

I've changed all of the electrolytic capacitors in the tone circuit,
I've tested and substituted the 4 main filter caps. I've check the
suppression network on the output.I this this is some sort of
decoupling
problem, but I've sent way too much time on this receiver. A friend
who
worked on these when they were under warranty has looked it over as
well, and we're both stumped.

Anyone in the group seen anything like this on a Luxman R117?

Many thanks,
Tim Schwartz
Bristol Electronics


Audio or ultrasonic osc?
What happens with reduced rails via variac?


Hello Nigel,

It's an ultrasonic oscillation, and a lower line voltage does not help.

Thanks for your time,
Tim
Bristol Electronics



I would try some extra/changed C over preamp low voltage supplies or try
some chokes in the prea rails