You are referring to U1? What could cause it to overheat in 2 min.? All the voltages check out, right up to the time it cuts out, the 5842s stay in check, B+ jumps to about 440V. I presume the B+ is jumping because the 300Bs are dropping out. Thanks for the help, this is my wife's amp and she's a little testy with me right now
You are referring to U1? What could cause it to overheat in 2 min.?
Poor / inadequate heat sinking.
Easy enough to verify if this is the cause, or not. Put a voltmeter on the regulator output and see if the voltage goes away when your amp cuts off.
HEHE...good idea...but I think she's faster than me."this is my wife's amp and she's a little testy with me right now" Run away!
Andy.
Would this be enough heatsink. I'm not exactly sure where to measure the output?Poor / inadequate heat sinking.
Easy enough to verify if this is the cause, or not. Put a voltmeter on the regulator output and see if the voltage goes away when your amp cuts off.
My last post was done while I was a passenger in a car going 70 MPH down I-95 on my phone. That's why it was rather short.
Your symptoms are exactly the same as a regulator shutting down. The filaments in the output tubes lose power causing the tube to stop conducting. This causes the plate voltage to rise.
Try pointing a small fan directly at the heat sink to see if it fixes the problem. If so make some improvements in the heat sink, or airflow around it.
My experience with 300B's showed that a single small heat sink could be adequate in some situations, while a large heat sink pirated off the CPU in an old PC was marginal. It all depends on the airflow around it.
The Sharp regulator used in the TSE has a thermal shutdown feature to protect it, but there is considerable variation between chips as to how hot they get before shutting off. Usually they are all too hot to touch when they shut off though.
Your symptoms are exactly the same as a regulator shutting down. The filaments in the output tubes lose power causing the tube to stop conducting. This causes the plate voltage to rise.
Try pointing a small fan directly at the heat sink to see if it fixes the problem. If so make some improvements in the heat sink, or airflow around it.
My experience with 300B's showed that a single small heat sink could be adequate in some situations, while a large heat sink pirated off the CPU in an old PC was marginal. It all depends on the airflow around it.
The Sharp regulator used in the TSE has a thermal shutdown feature to protect it, but there is considerable variation between chips as to how hot they get before shutting off. Usually they are all too hot to touch when they shut off though.
Poor / inadequate heat sinking.
Easy enough to verify if this is the cause, or not. Put a voltmeter on the regulator output and see if the voltage goes away when your amp cuts off.
Or see if heaters are still glowing.
Thanks George...and to others. I bought a new heatsink that should do the trick, and some thermal paste, too.
Unless the valve is directly heated I have never found a need for dc heaters.
In the numerous designs I have built any problems with hum have always been other problems and not the heaters.
I'll check that next time I fire it up. I do know the heat on the outside of the tube drops. Thanks.Or see if heaters are still glowing.
Unless the valve is directly heated
The TSE is designed for one of three different tubes, all are DHT's. In this case 300B's which don't produce much filament glow, but it should be visible from the top in a darkened room.
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- TSE loses bias after about 2 minutes