a tube primer for guitar and bass players - Guitar Amplifier Blueprinting

7025-Y from the Ei factory
Gain: 90 Output: 46% QA: 25% - 60%
Long smooth plates, the most bright of the current tubes. The graph on this tube is at the start of this
paper. These are the characteristic sound of the Fender Tolex years. These are very articulate. In
V1 and V2 of a Fender Tolex era amp, these give the original sound signature. These tend to be too
bright in Marshall Plexi era amps for some tastes when used with a Strat or Tele, but if you tend to
load these amps down with pedals in the front end, they can help resolve the loss of treble from the
pedals. Long plates can tend to be microphonic in combo amps. The Ei factory was the OEM for
many “premium” tubes folks in the past, such as Siemens and Telefunken at times, so if the plate
structure looks familiar, this may be a clue.
http://www.groovetubes.com/product.cfm?Product_ID=1588
These are VERY inconsistent from the Ei factory. Over at GT, their reject rate can exceed 60% and I
saw one batch go through test where Groove Tubes tossed 90% of them. These are the tubes that
many other vendors just pass on along that do not test, so beware. When you find a great one of
these though, they are magic. They are very close to the original long smooth plate Telefunkens, so
close in fact, that some folks screen these with Telefunken logos and counterfeit them. Look for a
diamond molded into the base of real Telefunkens to be sure when buying NOS.
These are some NOS 5751 tubes. The famed GE 5 star is on the left, another NOS
in the middle, and the RCA Command Series black box plate is on the right.
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