VVR Issue
Moderators: pompeiisneaks, Colossal
VVR Issue
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.
"It Happens"
Forrest Gump
Forrest Gump
Re: VVR Issue
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
Rectifier -> Reservoir Cap -> VVR -> B+1 -> 4k7 -> B+2...etc
Re: VVR Issue
Awesome , I read about that but was unsure. It seemed the capacitance in my fluke calmed it down. Thanks
"It Happens"
Forrest Gump
Forrest Gump
Re: VVR Issue
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.
"It Happens"
Forrest Gump
Forrest Gump
Re: VVR Issue
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
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Re: VVR Issue
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.