You are almost finished. And although the first temptation is to plug up the amp and turn it on,
I recommend taking the time to review all your connections. This will be time well spent as it
will tie together all the construction steps. Errors are more likely to stand out during this time
and it is not uncommon to find two or three errors (I always do).
After verifying that all of the above steps are correct, read through all of the following steps
before completing any of them. Once you have finished reading, it is time to begin.
Initial AC testing
Step 1
– If not already installed, insert a 2A, fast acting fuse into the rear panel mounted fuse
holder labeled “mains” and a 500mA (.5A) fuse into the rear panel mounted fuse holder
labeled “B+” .
Step 2
–
With the amp unplugged and no tubes installed
, turn the amplifier's power and
standby switches to “on”. These switches will remain on until all tests are finished.
Step 3
– Plug the amp's AC power cord into AC power.
Step 4
– The panel indicator should illuminate. Monitor for any unusually smoke or smells or
a blown fuse or hot power transformer. If anything unusual occurs, disconnect power
immediately and review connections.
Step 5
– With your multimeter on the 20 VAC scale (this is the only
AC
measurement we will
be making), put the two meter leads on turrets T63 and T65 (polarity is not important).
Step 6
– There should be about 7 VAC as measured at these two turrets.
Step 7
– After 5 min. of trouble-free operation, remove the AC power by disconnecting the AC
8
Testing
It is good practice to use a power strip with a circuit breaker and an on/off switch between
the wall power and the amplifier power cord as an improved electrical safety measure.
CAUTION
I
n case of any troubles, quickly disconnecting the power cord from the wall (or turn off the
power strip). You should not touch the amp or the amp's power switch until the amplifier's
power cord is no longer connected to AC wall power.
WARNING
CAUTION
Use of any fuse larger than recommended could cause severe and costly equipment
damage in case of an internal component failure or wiring error.
I recommend using a variable AC (Variac) supply with separate current and voltage meters.
This allows bringing the voltages up very slowly and provides more accurate monitoring.
NOTE
If you are uncomfortable with just turning on the amp and watching for smoke, I recommend
building an inexpensive Dim-Bulb tester to monitor and control current flow into the amp. A
quick internet search on “Dim Bulb tester” will give several diagrams and plans.
NOTE
When changing or installing a fuse, always remove the AC source by unplugging the amp.
Never use fingers to remove or insert a fuse into a panel mounted fuse holder. Instead, use
the fuse cap to hold the fuse when removing or inserting into the holder.
WARNING
8.1
The following voltage levels as measured, will vary depending on the AC wall voltage. The
measurements that I've listed were made with a wall voltage of 116 Vac.
NOTE
30 TubeDepot.com
Summary of Contents for JTM45+
Page 17: ...TubeDepot com 13 Drawing 5 5a Drawing 5 5b T65 T63...
Page 20: ...16 TubeDepot com photo 5 11a...
Page 21: ...TubeDepot com 17 photo 5 11b...
Page 27: ...TubeDepot com 23 drawing 5 15c...
Page 33: ...TubeDepot com 29 drawing 7 1...
Page 38: ...10 Schematic 34 TubeDepot com...
