Copland cta 505 service manual

Page 1

SERVICEMANUAI.
FOR

CTA - 505

Page 2

Bias adjustment for Copland CTA-505:

1 . it you put in a new set of tubes, you should first turn all 4 bias-
adjustment potentiometers P1 -P1 02, luily in counter-clockwise
direction.

2. Turn on the amplifier, and let it warm up for 1 minute.

3. Connect a voltmeter (on mV measuring range) with - to chassis ground
(use the earth point situated between the main power- transformer and
the right outputtranstormer j

Connect the positive + test-probe lrom multimeter to point 5 left, tor
measuring Bias lor tube V4 and adjust with P1 to 45 mV.

For tube V5 the measuring point is T lelt, and adjustment is done with P2

For tube V104 the measuring point is S right, and adjustment is done
with P 101.

For tube V105 the measuring point is T right and adjustment is done with
P102.

When you have adjusted all 4 tubes. please repeat, as the adjustment

of one tube. affects the other tubes slightly.

4. Let the amplifier heat tor 30 minutes, then please repeat point 8.

5. if the tubes have been used tor some time, the bias should already be
close to the right level, so you can start bias-adjustment at point 2.
(You don't need to do point 1)

6. 45 mV = 45 mA per tube (same value tor all 4 tubes)

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