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W/Repairs: Difference between revisions
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2. 12AT7 | 2. 12AT7 | ||
A) Add 1200 ohm 2W in parallel with V124-V214-V114. This | A) Add 1200 ohm 2W in parallel with V124-V214-V114. This | ||
bypasses 30mA around the tubes, reducing the heater current | bypasses 30mA around the tubes, reducing the heater current | ||
from 180mA to 150mA. | from 180mA to 150mA. | ||
B) Tek used XV214 pin 9 as a tie point. It must float when | |||
B) Tek used XV214 pin 9 as a tie point. It must float when | 12AT7 is used, because it's heater center-tap. | ||
12AT7 is used, because it's heater center-tap. | C) V114B and V214B grids must be biased 3V positive for | ||
successful operation of the Q154-12AT7 cascode. | |||
C) V114B and V214B grids must be biased 3V positive for | Details below. | ||
successful operation of the Q154-12AT7 cascode. | |||
Details below. | |||
3. OTHER TYPES - NOT TESTED | 3. OTHER TYPES - NOT TESTED | ||
12AZ7 requires supplement and grid bias. Curves == 12AT7. Meets Vhk. | 12AZ7 requires supplement and grid bias. Curves == 12AT7. Meets Vhk. | ||
12BZ7 requires supplement and grid bias. Meets Vhk. | 12BZ7 requires supplement and grid bias. Meets Vhk. | ||
12DT8 requires shunt R and grid bias. Curves == 12AT7. | 12DT8 requires shunt R and grid bias. Curves == 12AT7. | ||
6BQ7/6BZ7/6BS8/8BQ7A require series R + supplement + grid bias. | 6BQ7/6BZ7/6BS8/8BQ7A require series R + supplement + grid bias. | ||
HEATER-CATHODE BREAKDOWN | HEATER-CATHODE BREAKDOWN | ||