This is an old thread and these days there are so many misconceptions floating around the web that the truth is hard to come by. Long story made short: go to the RDH4 and look up the rule of thumb for output transformers. Then compare that with the offerings made and you quickly discover that most is the proverbial brown matter - a far too low inductance to even get near the stated frequency range at the stated output. Even some quite well known brands are suffering from this. I recently wrote to one well known firm and asked for the inductance of a particular output transformer - "we do not hold this information", yeah right how can they then state that it is capable of whatever performance?
Stated simply: the small cores cannot hold the amount of wire required for the required inductance at the required current for the required output. Just a matter of physical constraints.
Sadly many of the younger generation did not grew up when tubes were the only thing in town and saw the sizes of the transformers in use.
- inductance requirements
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