VVR for 100 watt fixed bias amps

[phsyconoodler]

I want to build a 100 watt Overdrive Rocket amp and want to install VVR.The existing circuits only go up to 50 watt amps.What would one have to beef up to get it working on a 100 watt amp?
   I'm thinking maybe a pair of mosfets and double the component ratings and a huge heat sink?
Any ideas?

[Dynaflow]

 Here's a quote from Ampgarage where Dana addresses the higher wattage (100 watt) model he hopes to get ready. He goes by Ur12 on Ampgarage I'm sure you know that, but for those that don't. Here's what he posted about it:

"I know that some have used KOC's kit in a 100 watt amp by paralleling mosfets. My only concern is that without the mosfets being balanced, one may draw more current than the other and as they heat up the condition becomes worse to the point where one mosfet gives it up leaving the total load for the other. You would also need some serious heat sink and probably a fan if you can get it to work reliably

I am working on a design for a 100 watt amp with VVR but it won't be a kit that can be installed in any amp. The power supply will be completely different and the OT is a custom design also. I have the chassis and trannys already and hopefully this will be a winter project."

 Other option would be to delve into the KOC stuff as it was mentioned that he used Cascoded mosfets in series. Obviously this stuff is over my head but I thought I'd post what I remembered reading and then double checked it. Here is the page I quoted from:

http://ampgarage.com/forum/viewtopic.php?p=98061&sid=c43a91cba852593e843c55d0f5666540


Regards,

Dyna

[FYL]

I want to build a 100 watt Overdrive Rocket amp and want to install VVR.

Dana's VVR solutions are really nice for small amps, but not for a big bad dumblish PPP, even with doubled pass transistors.

IMO you should use DC Power Scaling, either with an SB-1 or preferably an SF-1, both fitted with high voltage/high dissipation mosfets such as the IRFPE-50 and at least a 2°C/W heatsink.

[tubenit]

I am wondering if you could have fixed bias for each pair of power tubes? I think Kevin O'Connor covers that in one of his books?

And then create a VVR for one set of power tubes only  &  another VVR for power tubes and phase invertor only.

With respect, Tubenit

[FYL]

I am wondering if you could have fixed bias for each pair of power tubes? I think Kevin O'Connor covers that in one of his books?

Yes, you can use two bias tracking modules (one for each pair of tubes) and separately vary the B+.

And then create a VVR for one set of power tubes only  &  another VVR for power tubes and phase invertor only.

You may also use the PS modules in order to separately vary screen voltage. Lowering screen V while keeping a highish plate V can give some nice results tonewise with relatively big bottles such as the 6L6GC (not worth the bother IMO with 6V6GT's or similar "small" power tubes).

[phsyconoodler]

What are the results 'tonewise' when lowering screen voltages,and why would a 6v6 react any differently?
  I have used a pot to vary pI bias with very nice results.Low volume with lots of grind,but it does alter tone somewhat.

[phsyconoodler]

So what's the big deal with over 50 watt amps and VVR?Do they not make larger mosfets,heatsinks and other higher rated components?
   Maybe I can adapt a voltage regulator from my car!

[FYL]

What are the results 'tonewise' when lowering screen voltages

Different disto, fatter sound.

why would a 6v6 react any differently?

There are very small tone diffs when you use small medium slope bottles and vary screen supplies.

[FYL]

So what's the big deal with over 50 watt amps and VVR?Do they not make larger mosfets,heatsinks and other higher rated components?

Using larger everything solves only part of the problems.

Dana's design is nice but quite rustic, OK for small amps (sub 20-watt), marginally so for medium amps (40-watt class) but not sturdy enough for large amps. For instance track widths and creepage distances are OK for 150 mA/450 V, going above these values could have dire consequences.

Ditto for the bias system : crude and effective for small amps; but not robust enough for big bottles - a real bias tracker is a must there.

[phsyconoodler]

I'm giving up on the VVR for this particular amp and doing the power dampening instead.One pot.

I'll do some more research into voltage regulation and see what I can come up with in the future.

[kagliostro]

I found this schematic

it seems a bit more complete than the VVR we usually see here

maybe someone can say if is a good base to be modified to obtain a 100w VVR

Kagliostro

[FYL]

maybe someone can say if is a good base to be modified to obtain a 100w VVR

Hmmm, I don't think it would be a good base.

Something like the attached schemo - somewhat based on KOC's excellent Power Scaling approach - is IMO a much better solution.

In : plate V, screen V and raw bias V; out scaled plate V, scaled screen V and bias tracking scaled plate V. Two pots, one for setting plate and screen V, the other one for bias range.

The layo is a possible version, using a dual-sided board and 500V+ design rules where applicable.

[kagliostro]

Hi FYL

I spent some time studying your interesting version of VVR

as I have no study in the matter

can you give some further explanations on the operation

SORRY TO DISTURB

MANY THANKS

Kagliostro

[FYL]

Well, it's a pretty simple board by silicon standards.

Two functions, three sections.

We have first a variable voltage power supply trhu the big mosfets, one for plates, the other one for screens. Voltage is set by the pot and bound by the tail resistor, with Vout = Vin (R / Rt + R), modulo mosfet losses (insignificant in HV supplies). The two sections are tied with Vp = Vs.

As the board is designed for fixed bias amps the bias supply should adjust proportionally to B+, that's what Q4, Q3 and their glue do thru the 330K "sampling" resistor.

[kagliostro]

Hi FYL

If I've correctly understand

Vs IN = Screen Voltage input

Vs OUT = Screen Voltage output

X-1 / W-2 / O-3  = 1ML 500v pot connections

AGND GND = ground

Vp IN1 = Plate Voltage input

Vp' OUT1 = Plate Voltage output

Raw bias in RB = bias supply input

Bias GND BG = groud connection for bias

Bias out BO1 = bias out

Bias out BO2 = ????? <== what happen here ??

and also the pot on the right side of the schematic where is connected ? and which purpose ?? pot value ??

THANKS for any explanation about

Kagliostro

[FYL]

Bias out BO1 = bias out
Bias out BO2 = ????? <== what happen here ??

and also the pot on the right side of the schematic where is connected ? and which purpose ?? pot value ??

The pot is a 25 to 100KL bias pot, you may connect it across B01 and B02 and get bias from the wiper or add your own bias circuit after the tracker.

[kagliostro]

MANY THANKS FYL 

excuse me for my naivety

Kagliostro

[FYL]

excuse me for my naivety

Asking questions is always a Good Thing™.
 

[MakerDP]

Something like the attached schemo - somewhat based on KOC's excellent Power Scaling approach - is IMO a much better solution.

In : plate V, screen V and raw bias V; out scaled plate V, scaled screen V and bias tracking scaled plate V. Two pots, one for setting plate and screen V, the other one for bias range.

The layo is a possible version, using a dual-sided board and 500V+ design rules where applicable.

Sorry for dragging-up a very old post but....

Has this design been tried and tested? I am looking to VVR a 50-ish watt fixed-bias amp and would rather not buy a kit to do it.

[Ed_Chambley]

Something like the attached schemo - somewhat based on KOC's excellent Power Scaling approach - is IMO a much better solution.

In : plate V, screen V and raw bias V; out scaled plate V, scaled screen V and bias tracking scaled plate V. Two pots, one for setting plate and screen V, the other one for bias range.

The layo is a possible version, using a dual-sided board and 500V+ design rules where applicable.

Sorry for dragging-up a very old post but....

Has this design been tried and tested? I am looking to VVR a 50-ish watt fixed-bias amp and would rather not buy a kit to do it.

I have a 1987 Marshall build with a VVR.  Just used the heat sink from a computer's power supply and thermal goo.  Tracks bias.  I do not like it, but I don't care for VVR's in general.  It will take it down to whisper quite if you want.

After going building it, in retrospect I would just buy it from London Power if I were to do another one.  I did not enjoy the process, but maybe you will.  50 watts is not difficult.

[kagliostro]

Here you can find the schematic of Merlin's VVR devoted to big amps

as to have it working correctly you must arrange a small separated bias transformer PS

http://el34world.com/Forum/index.php?topic=17083.msg170283#msg170283

K
 

[MakerDP]

Ed:
What did you regulate in the amp? The whole thing? Just the power tubes? Just the power tubes and the PI?

Also, I enjoy building electronic circuits of all kinds. I was doing that kind of stuff before I was building amps. I don't really want to spend about $125 on a kit that contains about $40 in parts when I can throw it together from scratch in less than two hours. So yeah, I'll actually get a kick out of building it myself. Also, I want to customize it so that the "scaling" pot is a switching-type so that it is also the amp's main power switch. I did this on two other cathode-bias VVR installs and I love how it doesn't require any extra space on the front panel.

Kagliostro:
Thanks for that link. That was an interesting read. It reminded me that I actually have a Power Scaling circuit schematic in one of my London Power TUT books. I don't have the volume that fully explains PS, but I should probably just bite the bullet and spend the $65 on the book already.

[Willabe]

Also, I want to customize it so that the "scaling" pot is a switching-type so that it is also the amp's main power switch. I did this on two other cathode-bias VVR installs and I love how it doesn't require any extra space on the front panel.

That may be nice but, VVR and the old style PS have the highest DCV in the amp on that pot. I'd be a little nervous about running the extra wall voltage on that same pot.

Kevin always used a 2w military type pot for his PS circuit because of the extra voltage handling of not only the resistive track but for track to case ark over voltage. To my knowledge the VVR used a regular pot, unless he changed up at some point and was pretty close to it's limit depending on the amp circuit.

A cathode bias amp most times would have less DCV to deal with than a larger grid bias amp.


                      Brad       

[MakerDP]

Good to know. Thanks Brad.

[kagliostro]

From Merlin's VVR you can use only the B+ regulation circuit and discard the bias circuit part (if the amp is catode biased)


the circuit used by Merlin has the advantage that is planned as to use common pot for the regulation, the HV is managed by a transistor


and (if I remember correctly) only 1/2 of B+ pass through the potentiometer


K

[SoundmasterG]

Dana Hall's VVR was based on KOC's earlier version of power scaling that used pulsed DC. KOC's kits that he has sold for several years for power scaling work for any amp up to 500 watts and are easy to get working, though they do take some tweaking to get right. They also work differently than the earlier design and work well. I've used them on several amps and I like it a lot. They would be my first choice if I wanted to power scale an amp whether or 50 watts or under.


Greg

[MFowler]

Dana is a friend of mine so I'm reluctant to post this link but is for 100w amps.


http://www.skipzcircuits.com/FX100.html

[MakerDP]

Dana is a friend of mine so I'm reluctant to post this link but is for 100w amps.


http://www.skipzcircuits.com/FX100.html

Stephen at Trinity Amps actually recommended this guy to me as well when I asked him if he had a fixed-bias kit.

[keithv]

maybe someone can say if is a good base to be modified to obtain a 100w VVR

Hmmm, I don't think it would be a good base.

Something like the attached schemo - somewhat based on KOC's excellent Power Scaling approach - is IMO a much better solution.

In : plate V, screen V and raw bias V; out scaled plate V, scaled screen V and bias tracking scaled plate V. Two pots, one for setting plate and screen V, the other one for bias range.

The layo is a possible version, using a dual-sided board and 500V+ design rules where applicable.

So the scaled plate V would connect to the center tap of the OT and the scaled screen V would connect (probably through a resistor) to pin 4 of something like an EL34, KT66, or 6L6?

[HotBluePlates]

So the scaled plate V would connect to the center tap of the OT and the scaled screen V would connect (probably through a resistor) to pin 4 of something like an EL34, KT66, or 6L6?

Yes, same places the original fixed voltages ordinarily connect.