In article , Phil
Allison scribeth thus

** Hi,


this week a old customer donated his long out of use Luxman SQ65 integrated,
valve amp to me saying maybe I could fix it, sell it and make some money.

What an optimist, the amp is over 50 years old and still has most of the
original valves fitted - plus 3 missing. Some of the valves are oddball, like
6DT8s phase splitters and 7868 noval outputs - neither type available in
Australia.

The SQ65 is sort of famous for having both " motional feedback " controls and
using cathode feedback in the output stage (a la Quad II ) so I persisted.


Put it on the bench for basic tests, gradually winding it up with a Variac and
immediately found the main electros had depolarised.
[*]

Next I found the bridge
rectifier was only working half wave and even then with a huge voltage drop.

So I fitted a new bridge across the old one and after half an hour reached full
AC supply without smoke so I let it soak for an hour or so.

My ESR meter informed that the main (dual can) filter electro was worn out -
various others seemed still functional.

Then I checked the two output transformers with an ohmmeter and got strange
readings from the first but the expected ones from the other. The first tranny
proved to have an open primary winding - damn.

So fixing the thing for profit was completely out of the question.

I extracted the good output tranny and bench tested it using 240VAC across half
the primary and a 16ohm dummy load on the secondary. Ran it for several hours
until it got warm and saw no problems. At a pinch it might do as a replacement
in my a Quad II workshop amp one day.

Based on Googling, I discovered that if fixed and working well an SQ65 has
little value and there is simply no demand.

It will be going out on the next council clean up day.




.... Phil



* Any gear older then say 10 - 15 years electros are very big contenders
for changing especially in output couplers and power supply rails like
the old Quad 303, are there any UN-upgraded ones left now;?.

Recapped a HP 339A distortion test set here. Was a bit "quieter" on
residuals after that, same with an elderly Marconi 2035 mod meter and
some other now getting on but otherwise OK equipment.

Pity that you can't get the knobs for the 339A anymore, real pain making
up replacements they are..

--
Tony Sayer