[Boatanchors] Was a "mix" of 6V & 12 Volt tubes common in National radios?

[Phil]

I've been checking out this NC-140 a bit more, as well as studying the 
manual.  One thing that I noticed is it uses a mix of 12 Volt & 6 Volt 
tube filaments.  Three are 6V, four are 12 Volt, like the 12BE6, 12BA6, 
12AV6 and so forth.  The transformer has a 12 Volt filament winding with 
a tap at 6V for the 6V tubes and pilot lamps.  Seems like an odd way to 
do things to me. The rectifier is a 5Y3.

Also, the transformer seems a bit "small" for the tube complement and 
runs quite hot, even with the Variac set on 110VAC (looks like the 
filter can was replaced in 2010).

-- 
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

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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.
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           37 foot "Low Noise Vertical", 11 feet AGL for LF/MW/SW.
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Merced, Central California, 37, 18, 37N   120, 30, 6W CM97rh


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