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Eico ST40 tone issue

rudedogg

rudedogg

AK Member
Subscriber
Hey all, i recently picked up two Eico ST40 integrateds in excellent cosmetic condition. Both were “working” according to the seller. I DBT tested both and they did pass that. On the DBT, one had a very significant channel imbalance. I did a full recap on that one, including the loudness mod, and some resistors. The volume is now much closer between channels, maybe right on. But turning the balance knob changes the tonal balance as well! To the right decreases bass, and increases highs a bit. To the left does the exact opposite to that channel. Strange! I am thinking builder error somewhere… your thoughts please!
I can compare the two at some point… but wondering if anyone has had the same issue
 
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Ya check the wiring, sometimes the halves of the 750k pot are off. But that would indicate the soundstage isn't centred when it's in the middle position. The schematics, construction manual are all available on line.
 
Well i’ll be damned! I just hooked up my second unrestored Eico ST40, different builder, EXACT SAME issue!! Sooo it is a design flaw???
 
Did you make sure it's wired correctly?Check possibly the pins on the PEC board go to the right pins on the treble and bass pots. Something has to be wired wrong, I have restore a bunch of these over the years and they work well.
 
danno2000 said:
Did you make sure it's wired correctly?Check possibly the pins on the PEC board go to the right pins on the treble and bass pots. Something has to be wired wrong, I have restore a bunch of these over the years and they work well.
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Oh boy! I figured out the problem! It was not the amp(s) at all! It was my test speakers! Ratty but good functioning Nova 8b’s. I had recently tested a Yamaha PC4002m with them, i am guessing i fried the left side crossover! I hooked up the amp to my Polk 5jr test set and all is perfectly balanced!!! UGH! Lol
 
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