I would guess any tube whose structural elements are rigid enough to
maintain spacing and does not readily "short" when subject to
shock/vibration. This can be easily determined by energizing the amp with a
100 Watt clear light bulb in series with the line, and with all the tubes
installed, tapping on the tubes with a rubber handled screwdriver - while
observing the series line light for changes in luminance. Changes in the
light would indicate structurally unstable tube elements - meaning it is
likely the amp/tubes will short during service. Otherwise, I doubt you would
be able to discern any quality difference. The SVT is also tough to
balance - from what I recall, and can be very touchy.

Jim



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JAMES RUGGIERI
"roger" wrote in message
om...
Hi all,

I'm intending to retube my ampeg svt classic (reissue) with either
sovtek 6550we's or the electro harmonix 6550's. They're both priced
about the same, which would be the better choice? Thanks.