Quote:
Originally posted by DBerning
.....In fact, this Admiral is an interesting set .... Another interesting feature that lowers power consumption is the way power is supplied to the IF and tuner. The main B+ is perhaps 300 volts, but the voltage used by the IF is reduced to 150 V not by a power resistor, but with the audio output tube. Thus, the audio output tube is used sort of like a series pass voltage-regulator tube, but at the same time doing the work of the audio output.
Dave
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Hi Dave,
Welcome to the Vintage TV Forum! Your knowldgeable contributions will be appreciated. The clever DC B+ divider scheme using a 6AS5 miniature pentode in the audio output stage was not only employed in the 19A11 Admiral chassis but in some of their larger magnetic deflection chassis as well in 1949 for sure. I had a 12" set with a badly gassy 6AS5 with incandescent screen grid and not having an exact replacement found that more common similar tubes like 6AQ5 whch I did have in stock unfortunately had different pinouts. Determined to enjoy the set I raised a couple of resistor values in the audio output circuit to decrease the current through the tube allowing it to function until I could get a replacement. Before the mod it would suddenly avalanch completely into cutoff with no sound from a mild audio excursion. After replacing the tube I never bothered changing my resistor values back to stock. It worked fine.
That Tesla coil type HV supply in the 19A11 using a 6V6 is a real powerhouse compared to the T-54 series Hallicrafters 7" electrostatic sets. Halli does the same thing using one tiny 6C4!
BTW, I am very impressed with your very unconventional OTL amp design and sure would love to have the opportunity to hear one of these some day!
Rob