Tube Lab SE Problem

Doc Jr 8156 · 7th November 2009, 03:41 PM

Hello,
I had my TubeLab SE (with JJ 300Bs) running for more than 3 months now but recently I noticed that after 2-3 minutes of playing music the 300Bs will turn off while tyhe rectifier and the input tubes are still on. Never had this problem before. The 300Bs are biased at 75ma. The input tubes are at 170 volts. B+ at 340 volts. Can someone shed me some light on what is going on here? How can I narrow the origin of this problem? Thanks for your help.

Doc Jr 8156

BillEpstein · 7th November 2009, 04:28 PM

Isn't that the power drive overheating issue? Got a big enough heat sink?

Sendy · 7th November 2009, 04:29 PM

Quote:

Originally Posted by Doc Jr 8156

... the 300Bs will turn off while tyhe rectifier and the input tubes are still on...

It means 300B no heater voltage and other tubes yes ? May be defect on socket, may be on tube pin (lead free solder), or defect inside tube.

DigitalJunkie · 7th November 2009, 05:25 PM

IIRC it's an overheating issue with the Sharp regulator used for the filaments. Ya need a bigger heatsink.

Doc Jr 8156 · 7th November 2009, 05:29 PM

Thanks Bill and Sendy. Bill, the heatsink in there now had been there for 3 months and never had this problem before but I will investigate that. Sendy, maybe defect in the tube sockets? The input tubes and the rectifier remained lit when the 300B shuts off. The tubes were fine when tested on my other 300B amp though. Will it help if I'll install independent heater transformers? Thanks again.

Doc Jr 8156

Sendy · 7th November 2009, 06:20 PM

If you have another 300B, can you exchange and test amplifier with other piece 300B ?

tomchr · 7th November 2009, 06:41 PM

Doc,

If by "300B shutting off" you mean that the filaments turn off, read on.

There are many possible reasons for why you didn't see the issue earlier but is seeing it now. Maybe the heat sink has more dust on it now. Maybe the 300B filaments have aged and draw slightly more current. It is also possible that the AC line voltage has changed slightly, so now the Sharp regulator has a larger voltage across it and dissipates more power. It sounds like it's a marginal heat sink design to begin with.

Put a bigger heat sink on it. Use thermal grease between the regulator package and the heat sink - or at least a thermally conductive silicone washer. The stuff is available at DigiKey Corp. | Electronic Components Distributor | United States Home Page and elsewhere.

A new heater transformer will not solve the problem. A new heater transformer will not change the power dissipated in the regulator.

~Tom

Doc Jr 8156 · 7th November 2009, 08:53 PM

Hello Sendy and tomchr,
Thanks for responding.

Sendy, I will try other 300Bs n there.

Tomchr, the heatsink in there is only 1X1/2 inch square. I'll get a bigger one. On the original sink, I used both silicone wafer and thermal grease. What if i'll change the regulator to a 7 amp one instead of the 5 amp in there? Godspeed.

Doc Jr 8156

rmyauck · 7th November 2009, 09:18 PM

Try Arctic Silver used for computer CPU's etc. Works better than white grease. A computer CPU heatsink with fan may be worth a try. They can be found for free from discarded computers. Larger ones recommended. When cleaning fan and heatsink with compressed air or vacuum cleaner, hold fan so it doesn't spin as dirt seems to get in bearings easier when spinning.
Good luck,

Randy

rmyauck · 7th November 2009, 09:26 PM

I forgot to say you will need power to run fan. DC tube heater might have enough voltage. 5V might be enough and it will be quieter too. I believe fans run on 12V.

Randy

7th November 2009, 03:41 PM	#1
Doc Jr 8156 diyAudio Member Join Date: Oct 2004	Tube Lab SE Problem Hello, I had my TubeLab SE (with JJ 300Bs) running for more than 3 months now but recently I noticed that after 2-3 minutes of playing music the 300Bs will turn off while tyhe rectifier and the input tubes are still on. Never had this problem before. The 300Bs are biased at 75ma. The input tubes are at 170 volts. B+ at 340 volts. Can someone shed me some light on what is going on here? How can I narrow the origin of this problem? Thanks for your help. Doc Jr 8156

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7th November 2009, 04:28 PM	#2
BillEpstein diyAudio Member Join Date: Feb 2004 Location: The Great Smoky Mountains	Isn't that the power drive overheating issue? Got a big enough heat sink?

7th November 2009, 05:25 PM	#4
DigitalJunkie diyAudio Member Join Date: Apr 2003 Location: Portland,Oregon Blog Entries: 4	IIRC it's an overheating issue with the Sharp regulator used for the filaments. Ya need a bigger heatsink.

7th November 2009, 05:29 PM	#5
Doc Jr 8156 diyAudio Member Join Date: Oct 2004	Thanks Bill and Sendy. Bill, the heatsink in there now had been there for 3 months and never had this problem before but I will investigate that. Sendy, maybe defect in the tube sockets? The input tubes and the rectifier remained lit when the 300B shuts off. The tubes were fine when tested on my other 300B amp though. Will it help if I'll install independent heater transformers? Thanks again. Doc Jr 8156

7th November 2009, 06:20 PM	#6
Sendy diyAudio Member Join Date: Nov 2009	If you have another 300B, can you exchange and test amplifier with other piece 300B ?

7th November 2009, 06:41 PM	#7
tomchr diyAudio Member Join Date: Feb 2009 Location: Greater Seattle Area	Doc, If by "300B shutting off" you mean that the filaments turn off, read on. There are many possible reasons for why you didn't see the issue earlier but is seeing it now. Maybe the heat sink has more dust on it now. Maybe the 300B filaments have aged and draw slightly more current. It is also possible that the AC line voltage has changed slightly, so now the Sharp regulator has a larger voltage across it and dissipates more power. It sounds like it's a marginal heat sink design to begin with. Put a bigger heat sink on it. Use thermal grease between the regulator package and the heat sink - or at least a thermally conductive silicone washer. The stuff is available at DigiKey Corp. \| Electronic Components Distributor \| United States Home Page and elsewhere. A new heater transformer will not solve the problem. A new heater transformer will not change the power dissipated in the regulator. ~Tom

7th November 2009, 08:53 PM	#8
Doc Jr 8156 diyAudio Member Join Date: Oct 2004	Hello Sendy and tomchr, Thanks for responding. Sendy, I will try other 300Bs n there. Tomchr, the heatsink in there is only 1X1/2 inch square. I'll get a bigger one. On the original sink, I used both silicone wafer and thermal grease. What if i'll change the regulator to a 7 amp one instead of the 5 amp in there? Godspeed. Doc Jr 8156

7th November 2009, 09:18 PM	#9
rmyauck diyAudio Member Join Date: Apr 2009 Location: Northern Manitoba	Try Arctic Silver used for computer CPU's etc. Works better than white grease. A computer CPU heatsink with fan may be worth a try. They can be found for free from discarded computers. Larger ones recommended. When cleaning fan and heatsink with compressed air or vacuum cleaner, hold fan so it doesn't spin as dirt seems to get in bearings easier when spinning. Good luck, Randy

7th November 2009, 09:26 PM	#10
rmyauck diyAudio Member Join Date: Apr 2009 Location: Northern Manitoba	I forgot to say you will need power to run fan. DC tube heater might have enough voltage. 5V might be enough and it will be quieter too. I believe fans run on 12V. Randy

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