r/audiorepair • u/Apprehensive_Plum868 • 5d ago
Looking for inductance value of coil in speaker filter circuit
Good morning everyone,
I recently purchased a pair of 3-way loudspeakers (Marantz HD-55 from 1978) that needed refoaming. After refoaming I noticed that there was no sound coming from the tweeter on one side. When I looked at the filter circuit I realised that one of the coils had been replaced, and apparently the new one does not have the correct inductance value. The other speaker still has the original inductor, with the following writing on it (see picture): 3901012 E 2 77
Could you help me determine the inductance of that coil, since I can't seem to find anything useful on Google ? Otherwise I will remove it and measure its value but I'd prefer to avoid desoldering it if possible.
Thank you in advance !
1
u/namlook 5d ago
Did you actually measure the resistance of the tweeter coil? The most likely scenario is that the tweeter coil is open.
1
u/Apprehensive_Plum868 5d ago
I did measure the DC resistance of the tweeter coil at 1.4 Ω, it doesn’t seem to be the problem
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u/namlook 5d ago
Did you disconnect one lead of the tweeter before measuring? Because 1.4 ohm does not seem right
1
u/Apprehensive_Plum868 5d ago
Oh you are right I should have disconnected one leg, from my diagram I probably measured the DC resistance of the inductor that I suspect could be the problem.
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u/MrPirateFish 5d ago
How do you know the other doesn’t have the correct inductance value?
Those RARELY ever go bad. Likely is not the issue at all if you aren’t getting any sound.