Strange Sighting

DanP

New member
Well I've dipped my toe into the SET waters by purchasing an already completed, approx 5-year old SEX from another member.  First let me say that nothing this inexpensive should sound this good. And for reference, I am playing my Quicksilver Minuet Supremes (87.5dB) to comfortable levels in a small, acoustically live room (with sub). Now for my question: the RCA 6DN7 tubes that came with the amp do not appear identical to each other.  One tube has a small filament that runs just under the dome of the tube and lights up bright with power.  The other tube does not have this filament.  I looked at a set of Raytheon tubes and neither of them have this filament.  Can someone explain this?  Are these tubes OK to use as is?
Thanks.
 
Some have series heaters and some have parallel heaters. You can mix and match, no problem. They sound identical.
 
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