I don\'t know of a Model 300 unless it is a new one an Apex 300. With that number you have it sounds like an old Model called a Tektamet.
If you need your GrasebyGoring-Kerr unit tested or repaired,
give us a call at 1-336-969-0110.
We offer fair estimates and extended warranties on the work performed.
Shipping/Receiving:
Industrial Electronic Repair
145 Rockwell Place Ct
Tobaccoville, NC 27050
Phone: 1-336-969-0110