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Old 2nd August 2012, 05:01 PM   #1
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Default brief sound when switching off amp

Hi

i have been building the following layout:

http://www.turretboards.com/layouts_.../stock_mod.pdf

today i powered it up for the first time... after some waiting... nothing.. no sound.. no buzzing or humming... nothing... and then some smoke :-)

i then replaced the burned resistor.
(first resistor 1K over the first cap. 22uf 450v.)

i have checked everything again, for the 15th time and the i noticed i had the ground of the OT connected to the green wires... so i cut the wire and powered up the amp.

no smoke, still no sound.

very careful i felt the 1K resistor, it was hot, but not burning.

the i switched the amp off and accidentally i bumped my guitar, and then i heart sound slowly fading out.

now what did i miss?

i really could use some suggestions...
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Old 2nd August 2012, 06:20 PM   #2
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Quote:
Originally Posted by mrneedle View Post
Hi

i have been building the following layout:

http://www.turretboards.com/layouts_.../stock_mod.pdf

today i powered it up for the first time... after some waiting... nothing.. no sound.. no buzzing or humming... nothing... and then some smoke :-)

i then replaced the burned resistor.
(first resistor 1K over the first cap. 22uf 450v.)

i have checked everything again, for the 15th time and the i noticed i had the ground of the OT connected to the green wires... so i cut the wire and powered up the amp.

no smoke, still no sound.

very careful i felt the 1K resistor, it was hot, but not burning.

the i switched the amp off and accidentally i bumped my guitar, and then i heart sound slowly fading out.

now what did i miss?

i really could use some suggestions...
You need to post really clear pictures of your build.
Plenty of them, that shows everything.
You have a mistake somewhere that produces a short circuit.
You should not have replaced the resistor, and turned it on again. Not until you find the mistake.
You have another part burned out and it could be the transformer.
DO NOT operate the unit, until all the connections have been verified.
PHOTOS? PHOTOS?
You can make this much worse than it is, by turning it on again.

Operating the amp without a speaker load will blow the output transformer, bingo.

Last edited by soundguruman; 2nd August 2012 at 06:25 PM.
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Old 2nd August 2012, 06:53 PM   #3
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The caps in the layout do not show any polarity symbols. How did you orient them?

Do you have any kind of Volt meter?
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Old 2nd August 2012, 06:53 PM   #4
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soundguruman thanks for your reply, but i really can't take good photos of this build. it's all soldered to the tube sockets.

i'll order a turretboard and start over just to be on the safe side.
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Old 2nd August 2012, 06:55 PM   #5
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@loudthud

most of the parts came from the original PCB.

i looked at the polarity and matched it to the layout drawing.

and yes, i do have a volt meter.
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Old 2nd August 2012, 07:58 PM   #6
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There are no polarity makings on the layout. I have marked polarity on the attached layout.

Voltages at the tube socket pins would go a long way towards revealing where the problem is, but you may do damage to the amp while taking the readings. Check the polarities against the diagram. If any caps were installed backwards, they are damaged now, replace them with new ones.
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Old 2nd August 2012, 08:11 PM   #7
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thanx Loudthud i am going to check it again tonight.
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Old 2nd August 2012, 10:05 PM   #8
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ok i've checked everything twice. all de caps are in the right place with the correct polarity.

but still the same thing... i wait nothing happens.. i turn of the power, and then it briefly comes to life.
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Old 3rd August 2012, 12:39 AM   #9
asmith is offline asmith  United States
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You have something wrong in the bias supply. When you turn it off the bias supply is dropping faster then the B+. at some point the voltages are right for the tube's to conduct and you get sound.
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Old 3rd August 2012, 01:12 AM   #10
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Quote:
Originally Posted by asmith View Post
You have something wrong in the bias supply. When you turn it off the bias supply is dropping faster then the B+. at some point the voltages are right for the tube's to conduct and you get sound.
The amp is cathode biased.
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