I just got done replacing the 2 12" speakers in a vintage Kustom model 11-L amp. It sound great with a lot of punch and volume. But I noticed after about 1/2 hour of playing at a moderate level, the area around the T0-3 output transistors got very warm, borderline hot. The new speakers were lower impedance than the originals so I tried wiring them in series instead of parallel, but that didn't make any difference and it still runs hot. I could not find any specs, service info, or anything online about this model. Would anyone happen to know if it's normal for these to run hot. And btw I should mention the old speakers were destroyed by mice, not by the amp. I just want to make sure it's not going to burn up before I return it to the pawn shop I'm repairing it for. Thanks
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Kustom model 11-L normal to run hot?
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Are the transistors original ? Is there a bias adjustment trim pot ?WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personnel.
REMEMBER: Everybody knows that smokin' ain't allowed in school !
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The TO-3's are mounted on a heatsink (which may be a part of the chassis). It is normal that the heatsink heats up during use, just a question of how much.
What was the impedance of the original speakers, and what did you replace them with?Originally posted by EnzoI have a sign in my shop that says, "Never think up reasons not to check something."
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The original speakers had an unusual rating printed on the back. They say 8-16 ohm and they were wired in parallel. I replaced them with a pair rated at 8 ohms each. I had them wired in parallel when I posted this, and I've since put them in series. Made no difference on the heat. I have no way to measure the temp but it is hot enough to get uncomfortable touching for more than a few seconds but not hot enough to burn. I never dropped the chassis, only replaced the bad speakers. I suppose I should and check for trim pots for bias. Balance is good, very close to 0 VDC running. I know on something old like that a trim pot could have easily gotten more resistive or developed a bad connection. On vintage stereo receivers I'll usually put a drop of contact cleaner in and work it back and forth leaving it back at it's original spot because a sudden change in resistance can blow the outputs. I really should check this one and measure the bias voltage across the emitter resistors. Does anyone know where I could find a schematic or service manual or spec sheet that would tell the recommended bias setting? And don't worry about me getting shocked or damaging the unit. I forgot to mention I have a degree in electronics and 35+ years experience so I know what I'm doing. I was mainly curious if anyone knew if this model normally runs hot or if it has a problem. I didn't want to waste more time taking it apart if I don't have to. It sounds great and none of the controls are scratchy.
Btw how do I get notifications when someone replies on here. Just logged in to look at my post and see I have 2 I never got notified about. And thanks guys for the replies, much appreciated!
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Originally posted by steveh112@yahoo.com View PostDoes anyone know where I could find a schematic or service manual or spec sheet that would tell the recommended bias setting?
The notification system here seems to be hit or miss. Someone will post a question in a 10yr. old dead thread and the OP will get a notification and respond. Other times, no notifications like you are experiencing.
Originally posted by EnzoI have a sign in my shop that says, "Never think up reasons not to check something."
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I dropped the chassis out today. There are no trimpots for bias adjustment or anything so I put it all back and returned it to its owner. I wanted to attach a couple more pictures but it says I met my quota for uploads. Does that apply to just this one thread or anything else I post on here? And how do I get more capacity for uploads?
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Originally posted by steveh112@yahoo.com View Postit says I met my quota for uploads. Does that apply to just this one thread or anything else I post on here? And how do I get more capacity for uploads?
Originally posted by EnzoI have a sign in my shop that says, "Never think up reasons not to check something."
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