T.
:It would be easier reply if you'd name the model number of the radio that the battery is used in.
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:T.
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You would be correct about the voltages if this were a 3-way portable. However, it is not. The tube filaments are actually run in parallel, so you should only feed them 1.5 volts. A D cell, or perhaps two in parallel, should suffice. I am guessing that at the IF grid and plate I'm seeing 86 volts, and at the output plate I see 82, if that is in fact an 8. Even though the IF screen is connected directly to B+, it only measures 86 volts to the chassis, because the chassis is actually held somewhat positive with respect to the battery's B-, because there is a 470 ohm resistor between the chassis and the battery's B- terminal. This allows for a negative bias on the output grid. That said, you should use a 90 volt battery for the B circuit. If there is a Batteries Plus in your area, they carry the small 45 volt batteries, but they're expensive. In the long run you might be better off with 10 NI-MH 9 volt rechargable batteries strung in series. That way you can re-use them.
T.