Issue with squealing "Q" switch on 1976 Alembic Series 1

[Roy Vogt]

Hello Alembic Club Hive Mind,
I have a 1976 Alembic Series I (serial number A065).  I believe it's one of the LD Heater distributed basses.  I bought it a Guitars Unlimited Sales Warehouse in Ft. Worth Texas in Fall 1976.  I'm having a howl of feedback when I sweep the Sweep of the Tone Control with the "Q" switch set to it's sharpest notch.  I'm including a Youtube link as it better demonstrates what's going on:

I have a competent shop here that can so soldering (either Classic Ax or Low End).  I just need to know whether this is a tone control knob issue or one of the capacitors in the Q switch.  At this point I can't afford the $1200 electronics rehab (which may be more now), but just wish to fix this problem.
Any help you can offer would be most welcome.
Thanks,
Roy Vogt

[adriaan]

If you do a search here for "squeal", one of the first hits is this thread, where the issue gets resolved - https://club.alembic.com/index.php?topic=26769.msg272203#msg272203

[rv_bass]

Hi Roy,
I have had similar issues, but not quite the same, with older 70s Series Alembics.  I have resolved the issue by “excising the pots”.  To do this, turn the bridge filter back and forth its full sweep about 100 times.  The pots and switches  are self cleaning, so doing this can clean out any corrosion/oxidation that has built up over time, especially if you haven’t used the bass and switches in a while.  Do this procedure for the bridge Q switch too and all of the other control knobs and switches as well and see if it helps.  I’ve had to exercise each switch and knob 200+ times for difficult instances. I would try this first. Hope it helps!
Rob

[edwardofhuncote]

Just as a matter of habit, I rotate each Volume and Filter pot, and move each Q-switch 5 times, every time I plug in my older Series I. I don't move these dials very often when playing, so it's about the only exercise that they get.

[gtrguy]

Noisy all right! Just for starters I would swap the bridge and neck pickup leads around on the mother board and just see what happens. It could be a cap or something in the signal path in the Q switch circuit.

[KR]

My '77 presented the exact same issue. I got rid of the squealing by fully rotating the filter pot a couple of 100 times while setting the pickup selector on standby. I also exercised the filter Q switch many times.

[StephenR]

Had a similar squeal when using the pickup selector on my 78 Series bass after not playing it much for a number of years. "Exercising" the pots and switches always seems to help with any errant noises.