Quiana and Fandango 1.0 p 23
1. Let the power tubes cool. Remember the way the eight pins are arranged, and note
that the center hole on the tube socket has a keyway that matches the center post on
the tube.
2. Replace one tube. Turn the amp on. If the fuse blows (or the tube glows cherry red,
indicating an internal short), you've found the bad tube. Turn off the amp immediately. If
the fuse doesn't blow, replace another tube and turn the amp on again. Repeat this
procedure until you've determined which tube is bad.
3. When the tubes have cooled, remove them. Replace all power tubes. (Don't throw
away good tubes from the old set, though--save them as spares!).
General information about tube types
6L6GC is the most common of all American high power tube types, used in Hi-Fi, P.A.,
and Musical Instrument amplifiers for over 50 years. RCA built great ones as well as the
best coming from Sylvania. However, as we write this manual, there are only four
factories in the world building this tube; Svetlana in St. Petersburg, Russia, Reflector
(Sovtek) in Russia, JJ/Tesla in Slovenia, and a factory in China. NOS (New old stock)
supplies from various other factories are still available, albeit in short supply.
Unfortunately due to the conflict of NATO and Serbia, the Yugo 6L6 is no more, and it
was a poor tube anyway. Out of all that are currently made, we have had the best
success with the Svetlana, and some of the recent Chinese that are a copy of the
Sylvania, sold by Ruby Tubes. For EL-34, we use mostly Svetlana brand as well.
EL-34 has been the most common of high power output tubes used by European Hi-Fi
and Musical Instrument amplifier manufacturers. The tone of EL-34’s is very different
from 6L6GC. Besides the Chinese, Sovtek, Svetlana, and JJ/Tesla are the only EL-34’s
that are commonly available (as of the writing of this manual). We are very critical in our
testing of our tubes, and throw away many that do not make our grade. All of our amps
are built with matched tubes, that are graded as well. When you need to purchase
replacement tubes, if you order the same grade number that are in your amp originally
from the factory (provided that no one has changed the bias set at the factory), you can
change out the tubes without needing the bias to be re-adjusted. If you use tubes not
from us or of a different grade or value, you will need to have the amp rebiased. In
terms of 12AX7A types, there are only 3 factories that we know of building this tube
type; JJ/Tesla, Sovtek, and Ruby Tubes in China. Again, NOS stocks still exist of RCA,
G.E., Mullard, Telefunken, Sylvania, Mazda, and Philips. Usually the Chinese sound the
brightest and have the most gain. Recently the Sovtek 12AX7LP has been made
available and it is improved from it's predecessors, yet has less gain and less high end
than the Chinese. RCA, G.E. Philips, Mullard (NOS) are great tubes, but may need to
be selected for microphonics. We are using mostly Sovtek for the 12AX7A's. We use
12AX7WA or WB for V1-V3, and 12AX7LP/LPS for position V4 and V5. Together this
creates a tone and gain balance similar to running Chinese 12AX7’s.
(5 pages)
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