This matched pair new old stock-testing GE 6SN7GTB vacuum tubes was tested on our Jackson 648.  Tubes measured:

Tube One:  91 / 102 (91% / 102% 6SN7GTB and GE dot codes on glass; unbranded base)
Tube Two:  97 / 99 (97% / 99%  6SN7GTB and GE dot codes and K on glass; unbranded base)

On the Jackson 648 good range is from 70-130.

Listened to pair in our Alan Eaton amplifier; are dead quiet when the amps are muted; and have excellent frequency response, sound-staging, presence and 
dynamics (see pics).  Pair have black wing plates, short bottles and bases and a single side horseshoe double bar getter.  Tight on bases with no debris or rattling sounds.

These could possibly be manufactured for GE by Sylvania or Hytron.  Only guessing Hytron as I have another tube just like it branded by Hytron.

Check out our store for more tubes for your equipment needs.

Tubes ship via United States Postal Service (USPS) Ground Advantage with tracking for domestic U.S. sale; Priority is an option.  International orders ship via International Shipping service.  Package weighs eight (8) ounces.

Combined shipping always welcomed.

TUBES ARE GUARANTEED GOOD AND IN WORKING ORDER AT SHIPMENT. TRANSIT VIA POST CAN DAMAGE TUBES.  THIS IS NO FAULT OF OURS BUT THE 

THIRD PARTY ENTITY THAT IS DELIVERING ITEM(S) TO YOU, I.E, USPS, UPS, FEDEX, YOUR NATIONAL CARRIER IF INTERNATIONAL, ETC. PLEASE INSURE 

THEM! WE CANNOT GUARANTEE FAILURES ON YOUR EQUIPMENT AFTER POWER UP AS THERE IS NO WAY TO ASCERTAIN HOW TUBES WILL INTERACT WITH 

YOUR ELECTRONICS; NOR IS THERE A WAY TO DETERMINE WHETHER THEY MAY HAVE FATAL FLAWS IN TUBES THEMSELVES!  THESE ARE USED VACUUM 

TUBES AND TIME MAY HAVE TAKEN A TOLL ON THEM OVER THE MANY YEARS SINCE THEY WERE MANUFACTURED. WE CAN ONLY TEST FOR THE 

PARAMETERS MENTIONED ABOVE IN ONE OR MORE OF THE FOLLOWING EQUIPMENT WE USE FOR MEASURING:  TV-7/U, JACKSON 648 & MAXI MATCHER 2.