Mc 2105

bbpdoubleb

Member
I have a slight buzz in left speaker with no volume on, is there a certain thing in these amps to look for when we open it up? also the left meter reads higher than the right. Thx Bill
 
If you do a AK search, just over the last month, there have been a number of MC2105 and MC2100 (no meters) posts with owners looking for answers to their 40 year old amps issues.

These amps are 20 years or so beyond the expected service life of a typical capacitor so a recappping is past due.

Most likely a noisy transistor is beginning to show it is going to be a upcoming problem, but without a thorough bench test I am just guessing.
 
It needs to be bench tested first........otherwise you are just throwing you know what against the wall hoping something will stick.

A failing transistor is readily observable when bench tested and will get ahead of a possible cascading problem!!
 
The differential (long tail pair) transistors can get noisy and the bias resistor can drift higher in value pushing the distortion higher.

Much already has been posted about the driver transistor upgrade from the 80s. Most needed in the MC2300s it is applicable to the MC2105 also.

These are all critical to test. If they fail problems will cascade.

Recapping is now well past due but really is the frosting on the cake so to speak.
 
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