VVR

[labb]

Anyone have experience installing a VVR in a fixed bias amp? If so, what issues and how did it work out.

[TubeGeek]

I did try installing the VVR into a 5e5-a Pro amp but it wouldn't last long before it blew the mosfet.  I gave up and removed it.


I do like the VVR in cathode biased amps though.  One particular amp I find it works well with is the 18W.

[DLPublic]

I am hoping to install VVR (already have the kit) in my Vox AC15 build. (see http://el34world.com/Forum/index.php?topic=20416.0)

However, I want to get the basic amp up and running first before I add the VVR.  So it will not be for another month or so.

Dave

[labb]

Where did you get the kit? I have been trying to find Dana Hall but dont't seem to be able to find his web site any more.

[TubeGeek]

Where did you get the kit? I have been trying to find Dana Hall but dont't seem to be able to find his web site any more.

Yeah seems to be gone???


If he is no longer selling them, it doesn't take too much to build a point to point version.

[labb]

London Power has a version but they are kinda expensive...As to the 18 watt, I think that Dana has a brother that was active in the 18 watt site and that may be where he started developing his VVR. I know it was the first place in ran into them. I have one of his early VVR for cathode bias that I bought but never installed. It was for a 18 watt lite.

[pompeiisneaks]

Sluckey's AC15 is here on hoffmanamps.com if you want to build that one :)

~Phil

[Willabe]

London Power has a version but they are kinda expensive...

Yes but it is better quality, higher rated voltage/current mosfet, better circuit and better PCB, IMO.

He sells several different kits at different $$, make sure your looking at the right kit for your amp.   

[pompeiisneaks]

Oh sorry, I see, the kit is the VVR, ignore me ;) lol

[drew]

Dana Hall posted this on the ampgarage in February:

Hey guys. Here is the update on the VVR.

I have shut down my webpage for a couple reasons. First the company who hosted it kept raising prices on me each year. I'll probably move it to one that doesn't cost so much. Don't know when yet. You can get to me on Hall amplification group on Facebook. It is a closed group so you will need to ask to join.

The status of the VVR is in limbo at the moment. NTE also kept raising prices on the Mosfets to the point I could buy them in qty 1 from mouser cheaper than I could get them wholesale from NTE directly and I was buying 100 at a time. After a search I found another Mosfets but after the first bulk order the supplier also raised the price on those. It's getting ridiculous. I guess all these manufacturers are going to a marketing plan like gasoline or gold and changing prices from one order to another. Then Mouser quit carrying the PCB mount 1/2 watt pots. Discontinued them.
At the moment I have blank boards cathode bias available at $5 each (includes shipping). Probably have about 75 available at the moment if you want to source your own parts. I am out of fixed bias boards.

I haven't totally given up on supplying the VVRs but I need to go back and find some less greedy sources for the parts. I can have the pots manufactured but have to order a minimum of 1000. It's quite an outlay of cash on my part. I can also get Mosfets from overseas at better prices but I am researching the best way to go. I have made the VVRs available for the same price for 7 years now without raising my prices. It's just not economical for me to sell them anymore at that price point since everything else has almost doubled in price.

So there you have it from the horse's mouth LOL. It may take me a month or so to get it all figured out so bear with me and in the mean time if you want a blank board you can email me at jdhall0654@gmail.com.

Dana

[labb]

Thanks Drew, now we know

[PRR]

> kinda expensive...

Fix-bias amp needs not only B+ control but quasi-tracking Bias control. It is not a trivial design issue, and is likely to use about twice as many parts as a control for self-bias amps.

And as Hall's essay says, the electronics industry changes faster than small-time kitters can keep up. Prices on one part go up (or out) because another part got cheaper and took market share. All through-hole stuff is unwelcome in robotic PCB assembly, and the hand-made market isn't keeping those parts alive.

[DLPublic]

« Reply #3 on: July 26, 2016, 11:26:53 am »

Where did you get the kit? I have been trying to find Dana Hall but dont't seem to be able to find his web site any more.

To quote www.ampmaker.com (which is where I got my VVR/VCB kit.  It is only £18.50!)...

VVR was designed and refined by Dana and Richie Hall of Hall Amplification. The Amp Maker version is called VCB, and this version, VCB1, is for cathode biased amps. It's been successfully fitted to many amplifiers, from Champs, Deluxes, 18Wers, etc. It's also suitable for most Amp Maker kits.

Dave

[echidna]

I am hoping to install VVR (already have the kit) in my Vox AC15 build. (see http://el34world.com/Forum/index.php?topic=20416.0)

However, I want to get the basic amp up and running first before I add the VVR.  So it will not be for another month or so.

Dave

I know this is a long time later, but did you add the VVR? I started a clone AC15 7 years ago and shelved it, but with a bit of time on my hands recently finished it. i want to add the VVR but i can' work out how to add it. I have made the VVR, just need to know where to plumb it in, in fact, o only need to know whereto tap into the B+. Although my amp works a treat (channel 1 a bit quiet), i can't say i understand how this amp works and i have made loads of amps in the past. Is it pin 3 of EZ31 and C41? Would really appreciate this.

[tubenit]

Have you looked at the VVR schematics, layouts and photos in ARCHIVES !

http://el34world.com/Forum/index.php?topic=6899.0

With respect, Tubenit

[bmccowan]

I've installed VVRs in two fixed bias projects - A 6G3 and a Z-28 kind of thing. They were the Dana Hall devices. The instructions are attached - I think that's ok since he does not market them anymore. They include options for adjusting B+ for the entire circuit or just the power tubes - I went with the entire circuit option. Works good - better than ear plugs. I have not played either amp enough to know how long they might hold up.

[pullshocks]

Thanks for posting.  I never installed the VVR I got from Dana Hall and had lost the instructions.

[bmccowan]

had lost the instructions

Believe me, I was surprised to find them on my drive given my history of losing things! "Has anybody seem my capo?" Dan Hicks

[kagliostro]

Only one thing about the mosfet used, the NTE2973

it is a very expensive component, there are lot of way less expensive mosfet that can be used to build a VVR

--

Maybe you are interested to give a look here



Full schematic on the attached .pdf file


Note that the pot that control voltage is a double pot, 1M + 1M, this way they control both Plate Voltage & Bias Voltage

Franco