mike m said:

I checked the feed back circuit and all values are correct.
What am I not seeing?
Any suggestions?


I remember an article in some old issue of "Audio Engineering", called
"the sad tale of a half-watt resistor".
In which the author describes how a simple resistor in the feedback
loop path caused one channel to sound weak and distorted.
When measured with a Dc ohmmeter, there were no problems, but under
dynamic conditions, the resistor failed.

IIRC, this was also about a Dyna Mk. III.

Just replace them with ones known to be good and try.


I've also read in one of Menno's books about saturation of an output
transformer core in one direction. This usually happens when a large
current has flowed in one direction, e.g. when a tube shorts.
this results in weak bass reproduction and again, distortion.
The solution is to pull all the tubes from the unit, disconnect it
from everything and apply a variable AC voltage to the secundary
winding of the OT, from 0 up to ca. 20V and back.
That way, all Weiss-particles will return to a random state and the
transformer is able to transform again.

Dunno of this applies to your case, but if you decide to do this, be
very careful. If possible, connect the variac via a mains isolation
transformer for your safety.


If none of this helps, get the signal generator and the scope out.

--

"Audio as a serious hobby is going down the tubes."
- Howard Ferstler, 25/4/2005