Kustom model 11-L normal to run hot?

[steveh112@yahoo.com]

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

[loudthud]

Are the transistors original ? Is there a bias adjustment trim pot ?

[g1]

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?

[steveh112@yahoo.com]

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!

[g1]

Does anyone know where I could find a schematic or service manual or spec sheet that would tell the recommended bias setting?

For Kustom's, you will need to open and get the board number. Then you can check here: http://www.vintagekustom.com/literat...h/AmpList.html

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.

[steveh112@yahoo.com]

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?

[g1]

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?

The attachment capacity is limited for new users. After x number of days and some number of posts you will get the full privileges. Not sure what those numbers are though.