VVR Issue

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passfan
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VVR Issue

Post by passfan »

I have a recently installed vvr that I pieced together on my own into a tweedle dee deluxe. Power resistor is 15 ohm. Everything else is to spec and the mosfet is an nte 2377. Problem is when I attempt to turn it down it gets to around 70% and the amp freaks out with an oscillation. If I probe the b+ output with my meter I can run it up and down with no problem but as soon as I take the probe off it freaks out again.
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Forrest Gump
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Colossal
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Re: VVR Issue

Post by Colossal »

You'll want a reservoir cap in front of the VVR circuit. For a Tweed Deluxe...

Rectifier -> Reservoir Cap -> VVR -> B+1 -> 4k7 -> B+2...etc
passfan
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Re: VVR Issue

Post by passfan »

Awesome , I read about that but was unsure. It seemed the capacitance in my fluke calmed it down. Thanks
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passfan
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Re: VVR Issue

Post by passfan »

Well that calmed it down a bit and allowed me to turn it all the way down. I do still get a small amount of static between the 30 to 60 % sweep of the pot. Outside of that it's dead quiet.
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xtian
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Re: VVR Issue

Post by xtian »

The MOSFET needs it's stopper resistor (gate? drain? I've forgotten) mounted directly on the MOSFET to stop oscillation. Just like we mount the grid stopper resistors directly on our 12AX7s.
I build and repair tube amps. http://amps.monkeymatic.com
Ten Over
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Re: VVR Issue

Post by Ten Over »

As xtian said, try a gate-stopper resistor with a value of 390 to 820 Ohms soldered directly to pin 1 (Gate) of the MOSFET.
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