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. 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 Chinese for the
12AX7A's, but we may use a Sovtek in position V1 only. If you use Sovtek, or JJ/Tesla in
all of the positions (V1-V5), the amp will sound way too dark, and will lose gain and
headroom. It will sound like a blanket was placed over the amp.
Venus 5 Specifications:
High-gain input impedance:
1 Megohm
Low-gain input impedance:
33k ohms
Output impedance:
Selectable, 4 ohms, 8 ohms, or 16 ohms
Line Output impedance:
330 ohms minimum
Effects Loop Send Output impedance:
560 ohms minimum
Effects Loop Return Input impedance:
10k ohms minimum
