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Alpha 77

Is my rig ready for the 2-hole kit?

To determine if your amplifier is qualified, remove the top cover and unplug the largest ‘Amp’ connector from the transformer. Examine the pins on the transformer side and confirm that only one hole has a missing pin. If more than one hole has a pin missing, this transformer is not acceptable and a ‘Peter Dahl’ replacement should be obtained. Ask for the exact replacement transformer for the Alpha 77SX from Dahl.

Whether or not the suitable transformer is in place, another check needs to be made. Examine the chassis connector which mates with the large ‘Amp’ connector and make sure both filament circuits are in place. The quickest way is to insure that only one pin is missing from the connector. If more than one pin is missing, call for a kit and instructions. This is a minor problem but the items needed to complete this circuit are not normally supplied with the ‘two-hole’ kit.

Verify that a 3.125-inch hole exists in the chassis where the second tube is installed. Most radios have this hole with a cover plate over it. To check for this, remove the 12 screws from the RF deck cover and confirm that this hole exists. If there is no hole the radio must come to Atlanta to get punched. This condition in no way implies that the two-hole modification can’t be made.

Another minor limitation may exist on the CB-2 circuit board. Many early production models were outfitted with a reed relay as the ‘timer’ relay. No symptoms exist with only one tube, but the addition of the second tube intensifies the magnetic field around the transformer so much that the relay buzzes at 60 Hertz and modulates the carrier. The condition will be very obvious the first time you make power. If this occurs, the timer circuit must be reworked using a more substantial 24-volt relay.

 

With these conditions satisfied, proceed with the modification.

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