VVR Hints & Tips

[plumcrazyfx]

So with the help others on the forum I have my 5C1 EL34 + EF86 based proto where I want it to be before building the final amp.  This is going to be a practice/studio amp and it sounds best cranked to get just a bit of hair and sounds amazing especially with a boost or even with practically any other pedal - which was the goal. 

So since part of the idea was to be able to use it after the daughter goes to bed - I installed the simple VVR to regulate the whole amp (1m pot + 2x100k + 10ohm/5w + IRFPE50 + 12V zener) based on other threads here and it works great.  I just installed it between the rectifier and the 1st B+ cap - no standby (I'm a convert), no 1N4007 diodes, etc.

My question is most of those threads are older - a lot of them mention the NTE Mosfet that is $15+, etc. are there tips that have been learned about what works and doesn't work well with this design over the years?  I want this to be as problem free and robust as it can be - what are people's experience with reliability?  Also, what is the opinion of regulating the whole amp vs just the power amp?  Thanks.

[kagliostro]

There is a lot of channel N mosfet that can be used and has a very affordable price

--

I think you must try to lower only B+ for the power tube plate (or G2) and leave the voltage that arrive to the preamp tube untouched

Franco

[brewdude]

My experience is mixed.  Some amps seem much better with just the PA scaled, some with PA and PI, some with the entire circuit scaled. 

[dude]

You mentioned you like the VVR, scaling the whole amp...? Maybe leave it, do you have any noise issues, scratchy volume pot, when turned down low...?


al

[brewdude]

If you have a scratchy volume pot, you can add a capacitor (big enough to not restrict the bass frequencies), but you might need to move the grid leak resistor—input jack->cap->grid leak to ground->grid stopper.

[PRR]

The MOSFET is not a critical part; this is not a 200KHz switcher or a 800 Watt car-amp. The old devices are fine. You want a TO-220 case, preferably fully-insulated, >600V, >40W. All that other stuff the MOSFET bakers have busted their buns to improve in the last decade is pointless to us.

[plumcrazyfx]

I might do just the PA.  The cathode biased EF86 seems good but now hearing it again, the grid leak biased 6SJ7 gets really compressed and when fully turned down there is significant sag to the notes.

[dude]

A VVR wasn't meant to be turned down very low, doing so you lose highs and the amps "mojo".  Like playing your amp with a blanket over it. So, for all you who want to get that full tube distortion at whisper volumes, it's not happening.  That means doing the whole amp or just the power section.


Google "Dana Hall" or Hall Amplification, you can email him, he will answer you.


al

[plumcrazyfx]

It sound pretty good.  I've used attenuators for years and it's as good or better than that with this amp.  It only sounds overly compressed when cranked all of the way down on the one side.  I suspect it had to do with the grid leak bias.  I think having on the VVR on just the PA will solve that good enough for my purposes.