HOW CAN I MEASURE THE IMPEDANCE OF A VALVE OUTPUT TRANSFORMER?
To measure the reflected load, Ra-a, you need to make a voltage ratio measurement. Apply a low ac voltage (6.3v from a heater transformer is ok) to the secondary and measure the voltage on the primary (anode to anode). You can use a scope or voltmeter. The voltage ratio is the primary voltage divided by the secondary voltage you used. The primary impedance will be the ratio squared x the secondary impedance. For example, if the secondary is 16 ohms and the ratio 20 the primary is 20 x 20 x 16 = 6400 ohms.
