All talk and no data makes us a lousy liar! Let's look at some facts. These are plots generated by the famous HP8903B Audio Analyzer, using the GPIB software developed by Pete Millett (thanks Pete!) quote some time ago.
The plots are measured when the (Precision Series) output transformer is in ACTUAL WORKING circuit, instead of being under ideal environment driven by ideal function (frequency) generator. We are taking 2 output transformers as reference.
10K high voltage high impedance single ended output transformer
20Hz – 50KHz @ -2dB 60-80mA ACTUAL OPERATION
300B 3.5K single ended output transformer
22Hz – 50kHz @ -1.5dB 60mA ACTUAL OPERATION
211 use 10K Single Ended Output
Transformer, 20Hz @-0.5dB, 28kHz @-1dB|
300B use 3.5K output
transformer, 20Hz @ 0.5dB, 40KHz @ -1dB|