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Old 10-17-2020, 10:54 AM
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Stuart Stuart is offline
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Join Date: Apr 2003
Location: Minneapolis
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S&M Electrotech in Minnesota has replacement speakers that wlll work with vintage Delco radios: http://www.turnswitch.com/speakers.htm

They discuss the issue with modern 4 ohm speakers on their website:

Note: Many replacement speakers now sold by the discount stores, auto parts stores and mail order restoration parts houses are labeled as "4 to 8 ohm compatible" and are in fact 4 ohm speakers. These speakers can damage the older transistor radios. 4 ohm speakers will measure around 3.2 ohms with a DC ohmmeter. An 8 - 10 ohm speaker will measure around 7.4 ohms with a DC ohmmeter. The DC resistance is the critical number for the Delco radios as the output transistor is in series with the speaker. A properly operating Delco radio should have 1.5 volts DC across the speaker voice coil. A 4 ohm speaker will draw twice the current of an 8 ohm and cause the amplifier transistor (the half dollar size device mounted to the black finned heat sink on the back of a Delco radio) to run very hot.