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Author Topic: tube temp audio amp  (Read 4459 times)
KB2WVO
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Posts: 382




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« on: October 06, 2017, 01:46:10 AM »

from what i can tell.. HK SB110.
carrier generator circuit board

V6 and V8. if you know the manual .   from what i can trace down. the V6 is a 6eb8. its for 2nd audio preamp and audio output amp.
temp of this tube in idle is around 150F. i have a fan outside of case on top. drawing out. rite over the tube.

is this normal temp for a tube in idle? or is this signs of over voltage or age ?
tubes in red circles. 150F..

« Last Edit: October 06, 2017, 01:50:37 AM by KB2WVO » Logged
KE4OH
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Posts: 134




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« Reply #1 on: October 06, 2017, 05:04:53 AM »

Idle or not probably won't affect the tube temperature. I'm pretty sure those stages are running in class A, which means they are always drawing the same current regardless of the presence of audio.

Is 150F too hot? Nope.

By the way, you are using the wrong tool to measure the operating conditions. Instead of a thermometer, use a volt meter (and Ohm's law) to find out how much current is being drawn by the tubes. If there is a problem, it's most likely to be a leaky bypass or coupling capacitor. Cheap and easy to replace.

Say, isn't that an electrolytic bypass cap in the upper left corner of the board? If it's the original, just go ahead and replace it. It's very likely to be leaky.
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73 de Steve KE4OH
KB2WVO
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Posts: 382




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« Reply #2 on: October 06, 2017, 05:32:03 AM »

Idle or not probably won't affect the tube temperature. I'm pretty sure those stages are running in class A, which means they are always drawing the same current regardless of the presence of audio.

Is 150F too hot? Nope.

By the way, you are using the wrong tool to measure the operating conditions. Instead of a thermometer, use a volt meter (and Ohm's law) to find out how much current is being drawn by the tubes. If there is a problem, it's most likely to be a leaky bypass or coupling capacitor. Cheap and easy to replace.

Say, isn't that an electrolytic bypass cap in the upper left corner of the board? If it's the original, just go ahead and replace it. It's very likely to be leaky.
i understand half that lol ..

i will be going over the voltages sometime this winter. so ill use right tool then lol.. i just happen to be looking to place fan inside some how without marking up the case in anyway. felt the heat from that one area. i have the tubes list priced out. ill have to go thru the caps n res next and price/order them up. bummer not able to get the same parts from then. keep it looking orig..
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KC4ZGP
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Posts: 1637




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« Reply #3 on: October 06, 2017, 05:57:49 AM »


I see nine transformers all needing adjustment.

Did you make a set of steel alignment tools.

Paper tools don't work well.

Kraus
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N8FVJ
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Posts: 378




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« Reply #4 on: October 06, 2017, 06:50:42 AM »

Tubes in higher powered audio amps can exceed 300F
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G3RZP
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Posts: 8149




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« Reply #5 on: October 06, 2017, 06:52:49 AM »

The 6EB8 pentode section has a 5 watt dissipation rating, so it will run pretty hot. Doesn't sound at all excessive at 150F. The pentode is meant for video amplifier applications and quite likely was chosen for its high transconductance - 12500 micromhos.
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N8FVJ
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« Reply #6 on: October 06, 2017, 06:56:51 AM »

Higher powered audio amps have tubes operating at 300F. 150F is rather cool operating.
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KB2WVO
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Posts: 382




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« Reply #7 on: October 06, 2017, 11:09:13 AM »

ty for info.. just wanted to be sure i dont blow up anything . or have a issue brewing.

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KC4ZGP
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« Reply #8 on: October 06, 2017, 11:56:40 AM »


WVO,

Be careful. Keep one hand in the pocket whilst near high voltage.

Kraus
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VE7DQ
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Posts: 223




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« Reply #9 on: October 07, 2017, 02:05:23 PM »

Situation normal. 

In the SB-100 the audio output tube operates screaming hot as well.  Mine still has the original tube in it.  Years ago the electrolytic capacitor that was right next to the tube suffered heat failure and was replaced with another mounted under the circuit board.
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KB2WVO
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Posts: 382




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« Reply #10 on: October 08, 2017, 03:54:39 PM »

Situation normal. 

In the SB-100 the audio output tube operates screaming hot as well.  Mine still has the original tube in it.  Years ago the electrolytic capacitor that was right next to the tube suffered heat failure and was replaced with another mounted under the circuit board.

works for me.. so much to learn with good ole valve radios. but darn its sooo much fun.. kids today are missing out on soooo much .. sad it is..
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G3RZP
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Posts: 8149




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« Reply #11 on: October 09, 2017, 01:38:26 AM »

Also very sad is that the basics of analogue design don't seem to be taught any more. There seems to be a growing attitude of 'if it isn't digital, it doesn't exist'.
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KB2WVO
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Posts: 382




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« Reply #12 on: October 09, 2017, 10:17:13 AM »

Also very sad is that the basics of analogue design don't seem to be taught any more. There seems to be a growing attitude of 'if it isn't digital, it doesn't exist'.

so true... cell radios. all they know these days lol
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KC4ZGP
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Posts: 1637




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« Reply #13 on: October 09, 2017, 10:30:07 AM »


The communist, socialist, Leninist, Marxist, liberal goal: dumb down the masses.

Kraus
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KB2WIG
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Posts: 361




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« Reply #14 on: October 10, 2017, 06:19:54 AM »





Kraus,

You left out  "They".

KLC
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