Having owned several Berning amps I have found that NOS tubes do make a difference(tho not a large one). I also have settled on RCA as being the best fit for both the 270 and Siegfried amps. My understanding is that 5692 shouldn't be a problem to substitute for 6SN7's. The easiest and most accurate policy in these cases is to call the maufacturer. David has always been very responsive and helpful(via email).
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