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Post subject: Artificial CT Help
Posted: Sun Jul 17, 2016 9:05 am
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I have a problem with a deluxe reverb new build.
The PT has no center tap for the heaters so I'm using an artificial ct with two 100R resistors.
Each resistor is soldered to one of the lamp holder lugs, the other end of the resistors are tied together and go to ground.

On first power up the filaments only lighted on the rectifier, 6V6's and the PI tube.
All other pre amp tubes were dark with no output.

When I lifted the two ct resistors from ground the amp works but with the expected loud hum.

Any theory's on this. I'm not sure if larger or smaller value resistors would help.

Robert


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Post subject: Re: Artificial CT Help
Posted: Sun Jul 17, 2016 11:14 am
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It should work. I'd check the wiring from the phase inverter heaters to the rest of the gain/EFX/input stages. My bet is bad solder point or bad connection from pins 4 to 5 ---- on the tube next to the PI.


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Post subject: Re: Artificial CT Help
Posted: Sun Jul 17, 2016 12:39 pm
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BMW2002Ti wrote:
It should work. I'd check the wiring from the phase inverter heaters to the rest of the gain/EFX/input stages. My bet is bad solder point or bad connection from pins 4 to 5 ---- on the tube next to the PI.

Thanks for the suggestion BMW.
I had already checked for continuity from the pilot light to the first preamp tube but took your advise and checked again and found a loose solder joint from pins 4-5 on V3 when I moved the pins. Unfortunatley the tubes still didn't light up after I fixed that.

I had already unsoldered the two resistors from the pilot light so I decided to try the 100R resistors again.
I soldered two different resistors to a ground lug, soldered the other ends to the pilot light and temporarily clamped the ground lug to the PT lug and powered up the amp. Presto it's working. :D
There was probably a bad solder joint on my first try also.

Many thanks BMW. Your suggestion reminded me not to overlook the simple things.


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Post subject: Re: Artificial CT Help
Posted: Sun Jul 17, 2016 6:04 pm
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Good deal! Just an FYI... all heater connections are in parallel --- in Fender amps. So, you can measure the AC voltage across any tube's heater points. Whether the tube is in the socket or not.

:)


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Post subject: Re: Artificial CT Help
Posted: Mon Jul 18, 2016 2:34 am
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Problem after building a amp are always solder or wiring error. :lol:


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