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Check Herbach & Rademan’s summer bulletin (Vol. 46 No. 5). Stock # 21K731 C$4.50) holds 8 C size cells and needs rewiring and a new output connector. H&R is in Philadelphia (215/426-1700).
If you use alkaline C cells , Eveready E-93 or equal, you can operate 2 1/2 to 6 hours .