[Boatanchors] Autek QF1 Filter pots (long saga)

[hwhall at compuserve.com]

If one half of the dual pot is still working, you can determine if it's linear or log by disconnecting & checking with an ohmmeter. Rotate the shaft to halfway between the stops & then see if from the wiper lug to either of the other lugs is 1/2 the total resistance. I suspect that since the pots aren't volume controls, they are linear.
WayneWB4OGM

-----Original Message-----
From: Philip Atchley via Boatanchors <boatanchors at mailman.qth.net>
To: Boatanchors at mailman <boatanchors at mailman.qth.net>
Sent: Fri, Aug 12, 2022 9:42 pm
Subject: [Boatanchors] Autek QF1 Filter pots (long saga)

Hi All,

It's been many years since I've posted here, think Duane F (and his 
frogs) may still have been alive then.

Well, this may seem odd to all of you, but here goes, not exactly 
Boatanchors, but it is OLD.  I do a LOT of NDB (longwave beacons) DXing, 
been at it over 25 years and Selectivity (IF & Audio) is 'everything' in 
digging out the weakest ones buried next to stronger ones, carriers 
etc.  Now, my two primary (Yaesu) receivers both have excellent IF DSP 
(down to 50Hz) as well as audio peak filters for CW, very effective.   I 
also use a homebrewed audio filter centered on 440Hz with a 6.5 Hz 
bandwidth, yes, 6.5 Hz!  Really effective at the slow CW rates used by 
most NDBs. . .

HOWEVER, I've long been a fan of the Autek audio filter, had a couple 
QF1A's back in the day.  While they ring a bit at extremely narrow 
bandwidths,  they are still quite effective, and I always regretted 
parting with my last one.   The QF1A with it's extra notch filter is 
especially good, better than the plain-jane QF1.

Well, I hadn't seen one for sale in a long time (didn't look especially 
hard though).  Awhile back I found what I thought was a used QF1A for 
sale at HRO at the fair price of 49.95, (thought it was the 'A' model 
because their catalog number was QF1-ANA :-( It was described as 
"Scratched, one foot missing, working, switch needing cleaning".  Shoot, 
that's all easy stuff, so I ordered it with a big smile on my face.

Well, that's only half the story, it was NOT the "A" model, but the 
basic QF1.  Oh well, you win a few, lose a few.  Today after spray 
cleaning the filter switch and pots I tried it out.  At first it seemed 
dead, then I realized that it partially works, but ONLY if the 
selectivity pot is turned clockwise.  In checking I found that the front 
section of the dual pot is open. . .

Both pots (selectivity & frequency) are 500 K dual section and I figured 
I'd replace both while I'm at it.  The "broken" pot had obviously been 
replaced before as the solder job is sloppy. It also has a much longer 
flatted shaft than the frequency pot which has a round shaft. What I'm 
not sure of is the taper of the pots.  Any QF1 experts out here?  
Antique Electronics has pots that seem like they'd be suitable, I only 
saw audio taper, no linear (maybe if I dig deeper).  All at Mouser 
seemed to have knurled shafts.

AS A SIDE NOTE.  Autek has to have used what is the stiffest hookup wire 
ever made in this filter.  I mean, it's really stiff!   I've been at 
this electronics thing since around 1953 and I anticipate some possible 
problems safely connecting the wires to the new pots when I get them 
(some of the terminals have multiple wires).

-- 
<>< 73 From "The Beaconeer's Lair" ><>
Specializing in DXing NDBs (Longwave Beacons)
Phil, KO6BB,  http://www.qsl.net/ko6bb/

RADIOS:
YAESU:    FTDX-101MP Xceiver, Dual SDR Receivers (~2020)
YAESU:    FTDX-3000 Xceiver, DSP IF, 300Hz Roofing filter (~2019).
Icom:      IC-718 Xceiver, DSP.
Portables: Eton Elite 750 (2), AKA Grundig Satelite 750 (2020)
            Sangean ATS-909X2 (2021), Tecsun PL-990 (2021)
SDRs:      Perseus SDR,  SDRplay RSPdx
ACC:      MFJ-993B Auto Antenna Matcher.
            HOMEBREW 4 Port Antenna Multicoupler, Feeds 4 RX's.
            HOMEBREW Tunable LF-MF Pre-Amp.
            Ratzlaff 440Hz 6.5Hz BW CW Audio Filter.
ANTENNAS:  88 foot Long Ladder-line fed dipole, ~35 feet AGL for MW/HF.
            Top Loaded Tee (Dipole fed as single element) ~35 Feet AGL.
            Butternut HF-6V 6 Band Vertical, ~12 Feet AGL for 75-10M
            Ratzlaff Active whip, 5 Foot Long, ~22 Feet AGL For LF/MW/HF.
            Wellbrook ALA1530LN Loop For LF/MW/HF at ~17 Feet AGL
            Diamond Discone ~35 feet AGL for Scanner.
QTH:      Merced, California, 37, 18, 37N  120, 30, 6W CM97rh

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