Yes, great resources, in fact the guy that runs tapeheads worked for Pacific Stereo, is way knowledgeable, and a hella great guy as well.Welcome to the AK Crew, m'8.
Great to see your status-change
from "lurker" to "member".
No background on that "5.5",
but here's some look-see
for you.
AK- March 24/2013
AK- March8/2017
hifiene.com
tapeheads.net- June 30/2022
Also, make use of the
"Search" option (upper rt corner)
to garner more possible leads
for your dad's h/m/d receiver.
Q
hifiengine may have a service manual, or should at least have an owners manual.
Happy Listening,
Celadon