Specifications

I took some time to trace and re-designate the proper part numbers on the schematic, this
should help me allot, later.
Over-drive
There is an LED indicator on the front panel that displays when the grid current is being
driven into over-drive. The level of "trip" on the display is set at the factory for 120mA of grid
current. This level is "hard-wired" into the bar-graph display of the grid current, it can't be
changed without moving the sense line from one point on the driver IC to another point. I
would not recommend doing that.
Fig.4
At this point, I want to tell you about the bar-graph displays, and associated driver IC's. I
found the displays to be highly accurate and ultra-fast, even faster than my RF applications
VFD outboard meter. As long as the displays are calibrated properly, they can be counted
on for accuracy and speed. For an older design, it certainly is good, even by today's
standards. Fig.4 shows all the LEDs of the front panel, some lit, some not.
Step-start trouble
Even before I was able to power up the amp, I noticed that there was a sign of a problem in
the "step-start" system. There are a pair of fuses that are rated 1.5A @ 250Vac. These
fuses had been changed to 3 & 4A. rating, this told me that this circuit had been drawing far
to much current for some reason.