6080 tube always on even at power off

mike · 3822

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Offline mike

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on: April 22, 2012, 11:58:58 PM
Hi,
I'm enjoying the sound out of the Crack very much, but I have a small issue with one of the builds. If I plug the power cable into the amp, the 6080 tube would always lit dimly.

There is no problem with the sound, the voltage and ohm checks, just and odd problem as it doesn't happen to the other Crack amp I built. I've double checked everything and found no fault on the wiring. Any clue?

Thanks.


Offline Grainger49

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Reply #1 on: April 23, 2012, 12:38:12 AM
That is odd. Check the power wiring, the wires from the IEC Connector to the transformer.

It seems to me that if the heater winding for the 6080 tube produces voltage all the secondary windings would produce voltages.

There is just one winding on the primary side and that is the one wired to the IEC Connector and power switch.


Offline mike

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Reply #2 on: April 23, 2012, 04:22:07 AM
Thanks, Grainger.

I've tested the amp just now and it actually still runs/makes music even when the power switch is OFF. I'm guessing that the power switch is faulty since the wiring is fine. I will take test it with the multimeter later when the amp is cooler.


Offline Doc B.

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Reply #3 on: April 23, 2012, 05:57:22 AM
Be very careful. It sounds as if you may have a miswire at the IEC socket, which could put a high potential on the chassis. Definitely recheck those power input connections.

Dan "Doc B." Schmalle
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Bottlehead Corp.

Offline Grainger49

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Reply #4 on: April 23, 2012, 11:10:24 AM
First, heed Dan's warning, these voltages can kill or mess with your heart in a bad way.

If the input/power switch/transformer input AC wiring is right you have a bum power switch.  It is easy to tell by measuring across the power switch when it is off.  You should see full line voltage there when the switch is open.  I think I have seen/heard of a power switch that failed on and one that failed off.


Offline fullheadofnothing

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Reply #5 on: April 23, 2012, 11:39:02 AM
Probably worth pointing out that the safer way to check your power switch is to unplug the unit and check for continuity/resistance in each position of the switch.

Joshua Harris

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Offline Grainger49

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Reply #6 on: April 23, 2012, 02:05:38 PM
Joshua is right.  That is much safer.  I'm used to futzing around with 3 phase 480V live for my living.  Not recommended for the uninitiated. 


Offline mike

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Reply #7 on: April 23, 2012, 07:13:15 PM
Thanks, guys. I checked with the multimeter and it's the power switch. It doesn't break the connection at the OFF position.


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