Dana Hall's VVR Install: Marshall 50 watt Plexi; Not Scaling

[clusterstudios]

Hello All,  My first post here.  I just installed a fixed bias VVR into a 50 watt plexi (1987x circuit).  The amp came to me as a pre built clone with a PPIMV already installed.  I installed the VVR as per the VVR3 instructions.  All the voltages track as they should (I think).  However, at full VVR the lowest plate voltage I got was about 55 DCV (tracking from about 495 to 55 VDC).  Not sure if it should track to 0 or not (as per the SV1 kit sold by Kevin O' Conner).  Also, my guitar volume stayed the same throughout the range of VVR (very loud with no volume drop).  My PPIMV worked fine though. I mapped my VVR installation diagram to a schematic (see attached).  I've included voltages as well as some changes from the original layout the previous builder made (position of the standby switch, etc..).  If anyone here can see what I did wrong please let me know.  If you need more data, let me know.  Thanks.

Joseph

[d95err]

How loud did you turn the amp up before turning down the voltage with the VVR?

If you were playing relatively quiet (i.e. not pushing the power tubes), turning down the voltage could make little difference. If you cranked the amp and there was no difference when turning down the voltage, something is wierd.

[clusterstudios]

Main volume 4-5. PPIMV full to half. I swept the VVR from max to min with no noticeable effect. I was expecting some volume drop even at 4-5. For example: I just installed a Power Scaling Kit from London Power on a 100 watt plexi and it worked like a charm. Scaled evenly up and down the pot. Even went to zero, turning off the plates with the pot on max PS. As a test, I set it up running at about 60 DCV on the plates, main volume at 8-9, PPIMV at half and played a les paul through it. Sounded freak'n awesome. Dynamics with guitar volume, crunch, harmonic. Excellent system. A lot more parts on the board and a bit more involved to install compared to the VVR but it works great.

--------
Joseph

[Richie]

looks like the B+ in, is wired wrong, or you have an another wire going to high B+, going to the dropping power supply resistors. high B+ should just have one wire going in.. then one wire coming out of the board to High B+ in the amp.

[clusterstudios]

looks like the B+ in, is wired wrong, or you have an another wire going to high B+, going to the dropping power supply resistors. high B+ should just have one wire going in.. then one wire coming out of the board to High B+ in the amp.

thanks for the response. if i was trying to scale the whole amp, then you would be right, but since I'm just trying to scale the plates/screens then I need to split the B+ at the stand-by. One half of the B+ to the VVR, then on to the plates/screens and the other half (full B+) to the dropping resistor and on to the PI and preamp. That's how I understand it.

[Richie]

Ok, I've installed them in plxi type amps, but i've always scaled the whole amp. Maybe someone will come in to give you some info on the way your wanting to do your amp.