Bob Carver CHERRY 180 User Manual page 6

TUBE TESTER
The front panel meter may be used to test the tubes. Remove all the large power output tubes; plug
the amp into the AC wall socket with the main rear panel power switch OFF. Insert the tube you wish
to test into socket #6 (the far right front socket). Turn the bias control fully clockwise and turn the
main power switch ON. With a watch, time the warm-up period for exactly one minute and note the
current reading. Turn the amplifier OFF, remove the tube and insert the next one. You can hold the
tube with your bare fingers - it will not be too hot after only a minute, provided it was cool at the
start. Keep track of each reading, and repeat until all tubes have been checked. If any one tube does
not bias up or "runs away" with its current climbing substantially higher ~ 200% than the others, then
it must be replaced. It is okay to turn the amp on and off at will. Return the bias control to its original
position and put all the tubes back into their sockets. This completes the tube testing operation.
MATCHING OUTPUT TUBES
Matching output tubes is not necessary, thanks to the DC restorer. But it's fun to do anyway. Test each
tube as noted above, but write down the current on each tube one at a time. You will end up with six
numbers. The goal is to select two groups of three whose sum (from any three tubes) is as close as you
can get to a similar sum from the other group of three tubes. When you are finished determing the
the two groups, add up the current in each group and check that they are as close as you can get
them. This is a bit of trial and error; while you have them on the table in front of you and are adding
the currents up, you may have to switch a tube or two from one group to the other to get the closest
sums. Then install the first group in sockets #1, #3, #5, the odd sockets. Install the other group into
sockets #2, #4, #6, the even sockets. The socket positions on the amp are, from left to right, looking
from the front. 1,2,3,4. The last two positions 5, 6, are the front tubes on the right. The front left
tube is #5, then #6 is to its right.
SMALL TOGGLE SWITCH
There is one toggle switch on the top front. It controls the feedback as mentioned earlier. Thrown left
is classical, right is contemporary.
NEW AMPLIFIER SMELL
Like a brand new car, this amplifier possesses a "new amplifier smell". When powered up for the first
time, the fresh paint and recent skin oils on the tubes will create a new hot amp smell. It will dissipate
with use, usually requiring about six weeks of normal operation.
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