HQ-180 for $450?
 

I have observed prices on Ebay and elsewhere,
and they have been steadily rising for excellent
condition 180s -- the 180C goes for slightly less,
which is interesting, because I started on a
180 and thought it might have better sensitivity.

But I say again -- excellent 180As and especially
180AX version with no major marks on the cabinet
or front will continue to rise...

HQ-180 for $450?
 

The self contained circuits containing resistors and capacitors were often
used in the audio chain of receivers. Many schematics show the contents of
the integrated circuit at the side of the schematic - but if not, it is easy
to go to any tube design handbook and reverse engineer the components. As I
recall, all of the RCA tube handbooks contain the elementary design data
needed to determine how the chip should have been constructed.

Certainly not rocket science.

Colin K7FM