[Ron Ramirez]

Use Ohm's law to determine the amount of resistance needed to drop the resultant B+ from the Kolster transformer to a level acceptable for use in the 511. To do this, you'll have to hook up the Kolster transformer, turn the 511 on just long enough to measure the B+ on the plate of the 71A and then immediately turn the set off.

Philco Service Bulletin #5 calls for a 71A plate voltage of 148 volts @ 115 volts AC line. Taking into consideration today's higher line voltage and more accurate multimeters, what measured 148 volts in 1928 will measure around 160 or so today. Take the difference between actual measured voltage and 160, then use the following formula:

R = E / I

where R = the resistance in ohms you need, E = the difference in volts you wish to drop (actual B+ - 160), I = current in amps. Use 0.0345 (34.5 mA) for I.

Now, once you have the resistance, you will need to know the wattage.

P = I 2 R

where P = power in watts; I = current in amps; R = resistance in ohms.

I can't do a superscript 2 here, so know that I 2 is "I squared." Again, use 0.0345 (34.5 mA) for I.