Matched Output Tubes, are Mandatory for good results in serious Tube Power Amplifiers. Individual Bias adjustment for each tube is also mandatory to allow the cathode current of each tube to be the same value. This prevents magnetisation of the output transformer. Magnetisation of the output transformer lowers your available Low Frequency Power Output, as the transformer will start to saturate earlier thai if it was not magnetised. The actual Bias Voltage applied to each tube should also be nearly the same. If this differs significantly between tubes, you have a problem with one or more of the tubes, (probably worn out). Despite tube matching by the supplier, tubes still differ somewhat in gain, so some form of AC Drive balance control is of immense benefit. Be aware that tubes wear out, and change their characteristics drastically as they wear. I would discard, or re-match tubes showing as little as 20% difference, 50% are throwaways.
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- 6 posts total
- 6 posts total