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If the initial resistance checks are OK then you can install the 6SH7 and the 300B tubes. The 6SH7
tube is keyed and you need to match up the notch on the 8-pin valve base with the tube base.
Make
sure you don’t mix it up with the 5U4G(B) tube which is also an 8-pin valve base tube.
The 300B tubes
can only be installed one way in the 4-pin valve bases.
11.4.1 300B Filament Test
Turn the amplifier on. After a few seconds, the 300Bs should begin to glow. (You may need to look
down from the top to see the glow.) Turn the amplifier off. If all is well then let’s move on to some
more comprehensive testing. If there's a problem skip to the 'Debugging' section below.
11.5 Voltage Checks
If you're using a Variac take into consideration that the voltages you'll be measuring are
going to be a percentage of the full DC voltages: for example, with the Variac at 90V AC
instead of 120, you can factor in that the DC voltages will be down by 25%.
Install the 5U4G(B) rectifier tube.
Tubes Installed At This Point: All
Turn the amplifier on.
Worst Case Scenario
Installing the 5U4G(B) rectifier provides the amplifier with the various DC voltages (including the
HT) that it needs to operate; usually, if there is a problem with the build, it's going to be noticed here.
It's possible that, if there is a major problem, the fuse will blow — or you may get a burning resistor
or even see some smoke.
If anything alerts you that there is something drastically wrong then turn
off the unit ASAP, unplug it, and contact us at audionotekits@rogers.com before proceeding. We'll be
happy to provide you with advanced troubleshooting advice. Note: we may ask that you send us high
quality digital pictures of the internals of the amplifier.
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