This listing is for a ONE(1) TUBE with Matched PLATES
1953 WESTINGHOUSE (Sylvania-Hytron) 12BH7 TUBE (not 12BH7A)
Tubes Physical Characteristics:
- Etched in glass "12BH7" "-------" "E3E" as date code of manufacture May 1953
(note that this etching style appears to be that of Sylvania-Hytron but tube is inked with "W" Westinghouse logo)
- Long BLACK Centered PLATES
- Large Horseshoe 'D' Getter
- Heavy top-side Silver Flashing
- Thick copper & metal support rods.
- Two thick spiked Mica Wafer-Spacers
- Two black thoriated heat Cathode vents atop plates and 2nd Mica spacer/wafer
- Yellow lettering "W" Westinghouse logo, vertical ink '312' '322' (312=EIA code for Sylvania-Hytron)TESTING: TV7D/U Minimum Good (60-65% Tube Life) is a meter reading of 30/30 = 1,500/1,500 uMhos Gm.
Average Industry NOS 'Bogey' Operating in CLASS A1 Amplifier when tested at 250VDC Plate Supply
Voltage is a TV7 meter reading of reading 62/62 = 3,100 / 3,100 Gm at 11.5/11.5 mA plate current emissions.
(See last pics for Tung-Sol/RCA Data Sheet dated 1950 & 1955 to verify these 'Bogey' #'s for Gm & mA)
Test Results: -
Calibrated (07/24/2023) TV7D/U TESTED at 150VDC Plate Supply Voltage
NO Shorts, No Leakage, No Gas, No Apparent Micro-Phonics detected
TUBE IS WITH NICELY Matched Plates with a 2.8% Gm match
Tube 1:
Side 1: 63.6 = 3,280 uMhos Transconductance (Gm) at 14.9 mA (Ia =Anode Plate Current)
Side 2: 61.8 = 3,190 uMhos Transconductance (Gm) at 15.0 mA (Ia =Anode Plate Current)
Our test set: Dan Nelson restored, upgraded and calibrated (07/24/2023) TV7D/U with Digital Meter reading
Transconductance in uMhos (Gm) and mA (Anode Plate Current).
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