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 300e tube voltage is correct - high pitched noise!
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Distelzombie

Germany
176 Posts

Posted - 11/30/2016 :  08:41:47  Show Profile  Reply with Quote
Hi there

Since I bought a new tube (sbt11a) I had never really measured the voltage since I had no multimeter. Today I remembered that and I measured it with my multimeter.
So I measured it on the two contacts for the tube. It was 150V. :/ I googled and the result was that the sbt11a recommended voltage is 400V, which is only slightly more than the volts of the original tube. They are compatible, that's why I bought the sbt11a.
Anyway I tried turning the pot but it only gives me a voltage of 100v to 200v. The coil makes a high pitched noise when I turn the pot in any direction. I know that that's not necessarily a malfunction, but together with the low voltage I think something is broken.
(I remember it was very hard to make tube work after I first touched the pot. Now it's working anymore)
Also I found that sometimes when I touch the metal case of the tube it measures a constant high. Don't know why it's only sometimes, but I guess it's static electricity?

Does anyone have a clue what's wrong?
Edit: forget the voltage. I was measuring wrong. What's with the high pitched noise?

GMC-300E+ V4.20 with sbt-11 alpha tube

My statements are to be taken as stuff-a-hobbyist-says.

Edited by - Distelzombie on 11/30/2016 08:56:18
Reply #1

Distelzombie

Germany
176 Posts

Posted - 11/30/2016 :  08:53:53  Show Profile  Reply with Quote
Oh glob, I'm stupid. I could've read the thread for how to measure tube voltage...
Anyway, there's still the problem with the high pitched noise when the voltage is correct. How do I get rid of this?
I know I need to either lower or higher the frequency of of the circuit, but right now I only have the pot. And in original condition the noise is not notable.
Also, with the correct voltage the tube is not working. But it was - a few moments earlier. I still think the tube is OK. The circuit just makes not sense right now.

GMC-300E+ V4.20 with sbt-11 alpha tube

My statements are to be taken as stuff-a-hobbyist-says.
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Reply #2

ZLM

1055 Posts

Posted - 11/30/2016 :  23:47:12  Show Profile  Reply with Quote
"high pitched noise" from where? speaker? how about the LED?
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Reply #3

Distelzombie

Germany
176 Posts

Posted - 12/01/2016 :  03:05:14  Show Profile  Reply with Quote
It's from the coil. If I put a magnet near it the pitch changes. It's actually about 3khz to 5khz and not "high".
That's because the circuit which provides the high voltage oscillates with thus frequency, which just happens to be audible. I know it's possible to change the frequency but have the same voltage output. I just don't know how in this case (well, except putting a magnet near the coil)
The led? It works normal.

The tube is now working. But the noise is still there. It's not very nerve wrecking, but it's new and I'm afraid of new stuff!

GMC-300E+ V4.20 with sbt-11 alpha tube

My statements are to be taken as stuff-a-hobbyist-says.

Edited by - Distelzombie on 12/01/2016 03:32:41
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Reply #4

Distelzombie

Germany
176 Posts

Posted - 02/19/2017 :  16:57:54  Show Profile  Reply with Quote
ZLM You never answered me if the noise is a normal behaviour.
I know from building a joule thief that it CAN be ok. The device seems to work normally, but i dont want to blow one tube after the other in case it realy is a fault.

GMC-300E+ V4.20 with sbt-11 alpha tube

My statements are to be taken as stuff-a-hobbyist-says.
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Reply #5

GBG12

Canada
25 Posts

Posted - 02/26/2017 :  17:04:47  Show Profile  Reply with Quote
My guess is that the inductor has developed a mechanical gap or looseness that was not there before, and now the oscillating magnetic field is making some small physical movement. Try using a blunt toothpick or plastic rod to press the inductor and see if the noise stops. If so, maybe a drop of crazy glue or nail polish will silence it again.
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Reply #6

Distelzombie

Germany
176 Posts

Posted - 02/26/2017 :  19:25:10  Show Profile  Reply with Quote
Yeah... But... It... ah, You know, who cares. It works fine. I cant really hear it as long as I dont change the tube Voltage. The end. '(fadeout)

GMC-300E+ V4.20 with sbt-11 alpha tube

My statements are to be taken as stuff-a-hobbyist-says.
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