Strange rag-chewing HW-101 problem (long)

[Charles]

I discovered a bad solder joint on the lug where the ALC diodes
connect to the wiring harness... the wires moved when the harness was
pulled. In fact the solder had never been flowed far enough down the
lug to where the wires were attached. Eureka?  Nope :(
Diodes are good, too. Still no ALC voltage. So I fired up the scope...

There is about 40 volts p-p of RF at the grids of the 6146's at max
drive. The bias is about -60v (the resting cathode current is set at
the meter triangle mark which I think is 50 ma). So the grids are
nowhere near being driven positive. Consequently there is no grid
current, no grid rectification, and no ALC voltage!

When setting the mode switch to TUNE, the ALC line is forced by the
MIC/TUNE LEVEL pot anywhere from 0 to -40 volts depending on the
output level, so that works too.

Tell me if this makes sense... there is not enough drive to push the
finals into grid current,  so ALC is not being developed, so the 1st
IF (among others) is turned on too hard, and therefore overheating.
The flattopping at high mic gain is most likely coming from an early
(audio) stage in an attempt to get enough drive to push the ALC loop
into "regulation",, not because an RF stage is being overdriven!

It looks like I should be trying to find why there is NOT excessive
drive with the ALC line at zero.

-Charles
WB3JOK

-----------------------------------------------------------
Products bought, sold or traded here is the responsibility of the
parties involved.  This list and the City of Tempe are not responsible
for losses or misrepresentations of any kind.  Buyer beware!

-----------------------------------------------------------
This list is a public service of the City of Tempe, Arizona
-----------------------------------------------------------

Subscription control - http://www.tempe.gov/lists/control.asp?list=HEATH
To post - HEATH at LISTSERV.TEMPE.GOV
Archives - http://listserv.tempe.gov/archives/HEATH.html