[Boatanchors] Update on the National NC-140 that's on the bench

[Phil]

OK, today is the first chance I've had to fire up the NC-140 on the 
variac and run some preliminary tests (had a Kenwood Dual Bander on the 
bench til today).

The owner reported that it needs alignment, and possibly some audio work 
as the audio doesn't sound right.  Here's what I found so far.

1. Sensitivity seems way down, even on the AM BC band.  Tuning bandwidth 
seems extremely broad on BCB stations (didn't test SW yet).

2. Audio weak and heavily distorted.

3. Slipping main tuning dial cord.

Further testing showed that the audio problem is actually an AGC 
problem. Turned the RF gain control down and suddenly the audio was 
clear and had plenty of volume, and the "S" meter responded to tuning.  
I suspect the IF strip is clipping until the RF gain is turned down.

Ran out of time today.  Tomorrow I'll pull the chassis and run some 
tests.  Good possibility I'll find a leaky cap.

QUESTION:  I seem to recall that use of a rosin block (for a violin bow) 
is a common fix for slipping dial cords.  Never used one, always 
restrung as needed.  IF the dial cord is otherwise in good condition, 
should I try it, or just order the cord material (assuming the springs 
aren't stretched)?

If this tube radio work catches on again here, I may eventually have to 
get a tube tester (again) :(  Many years ago when the table I used as a 
bench collapsed under the weight of an R-390A, and nearly put the radio 
on my foot, wifey laid down the law concerning boat anchors!  I gave 
away the really nice Hickock, then later also gave away the smaller 
"service type" tester I bought from a local ham.

-- 
73 From "The Beaconeer's Lair"
Specializing in DXing NDBs (Longwave Beacons)
Phil, KO6BB,  http://www.qsl.net/ko6bb/
KO6BB/B beacon, ~20W on 28.290 MHz, Ringo Vertical

HF/LF RADIOS:
HOMEBREW:   7 Tube+Rect 1v3 Regen RX for LF (built 2015)
Icom:       IC-7200 Xceiver, DSP IF & filters (~2015).
Kenwood:    TS-450SAT Xceiver, cascaded 250/125Hz Inrad filters.
10M Beacon: 2 x Realistic HTX-100's on 28.290MHz
SDR:        Softrock Ensemble II LF (built from a kit 2017).

ACC:   HOMEBREW  LF-MF Pre-Amp, 8Hz Audio Filter.
        HOMEBREW  4 Port Antenna Multicoupler, Feeds 4 RX's.
        
ANTENNAS: 88 foot Long Ladder-line fed dipole, 35 feet AGL for MW/SW.
           Active Mini-Whip, 36 Feet AGL for LF/MW/SW.
           37 foot "Low Noise Vertical", 11 feet AGL for LF/MW/SW.
           Cushcraft AR-10 Ringo Vertical, 14 feet AGL for 10M beacon.
Merced, Central California, 37, 18, 37N   120, 30, 6W CM97rh


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