Based on my limited knowledge, output trannies are very important in the standard direct coupled SET mode. Output trannies for parallel feed amps (like doc bottlehead's) are much less important. Output trannies for PP are also less important, though for UL they may make soem difference. POwer trannies i think make much less difference, assuming they are a hammond or above.Bottom line, i think output trannies matter only in the direct coupled mode SET config...the good ones sell for about $600 a pair!
Even the James trannies in my custom SET 45 sell for about $200-$250 a pair.
The output trannies in a parafeed config like the bottleheads would sell for much less (they are much less critical and their mfg requirements are much less)..my guess would be $20-$50 a pair.
thanx
akhilesh