Mosfet VVR question

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bandade
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Re: Mosfet VVR question

Post by bandade »

Thanks for the info guys. I didn't mind paying the extra 7 or 8 bucks for something I have heard is very reliable especially when you are already spending 5-800 on amp components; I just dont want to keep burning up my $10 bills.

I put the circuit in an 18 watt build the first time but this time around Im putting it in a Liverpool style amp. Has anyone compared a VVR to a PPIMV in the Liverpool?
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UR12
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Re: Mosfet VVR question

Post by UR12 »

NEjoe wrote:The NTE2973 is a perfectly fine part, but it's overkill in every single direction for many, if not most, situations. I'll concede that if you're selling a kit you have to try and prepare for anything the general public might do (even when you say not to) and that will likely lead to using the most indestructible part possible. However, that's an entirely different criteria from what I'm doing. And it sounds like the original poster might need a price break from the NTE part.

Ridiculous overkill is fine, and if the NTE cost a few pennies more I might give it a shot. However, when that overkill comes with a fairly hefty pricetag.... $10 versus $2 or $3 for any appropriately sized device....well I'm not interested. Besides, the NTE2973 is overpriced. Parts with even more power dissipation capability (350W for a STW15NK90Z) and equal or better specs still cost less than $7.
I also really like the built in back to back protection diodes the ST offers, no worries about picking 12V or 6V diodes and no polarity concerns since both directions are covered.

But that's just my opinion, worth exactly what you paid for it. 8)

It's been over 3 years since I posted the schemattic for the VVR on the internet for anyone to use for free. I have posted many many times that you don't need to use the NTE part if you don't want to but having said that the part you pick needs to be able to fit some of the design parameters for the current limiting circuity on the VVR to work properly. Mainly the RDSon resistance. The STW15NK90Z should work fine at .55 ohms RDSon but if you decide to remove the external zener that I use then you will have no current limiting. I would suggest to anyone that if that is what you want to do then by all means at least add a fuse to protect the mosfet, etc. Of course that will cost you another few bucks for a fuse holder and fuse so I don't see the cost savings. Also keep in mind that the specifications on the mosfets change as they get hot. So if you go with a smaller mosfet you may need to add an external heatsink in addition to just bolting it to the chassis to keep it cool.

In regards to the NTE being "Ridiculous Overkill" and "over priced" I would just point out that that is what I supply with my kits. I don't sell Mosfets. Even with the "Ridiculous Overkill" and "over priced" NTE part included with the kit, my kit is still priced lower than any other variable power kit on the market and comes with 15 pages of instructions. I feel it's a great bargain for anyone who doesn't want to try and roll their own. If you do want to roll your own then the NTE parts are sold at ma and pa Electronic stores through out the country. You may pay a little more for a qty one over the counter at the local stores but at least you won't be paying shipping in addition the the cost of the part if you had to order it through a larger cheaper supplier. I doubt that most smaller cities that have a electronic parts store would be carrying the STW......Z parts in stock.

You stated that "Thats entirely different criteria from what I'm doing". So what is it exactly you are doing?
NEjoe
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Re: Mosfet VVR question

Post by NEjoe »

UR12, I don't think your kit is overpriced, and never said it was. I think the use of a NTE2973 by people doing their own VVR is ridiculous overkill for most users, including the original poster. And yes I think the NTE2973 part is overpriced, by about 25%.

What exactly am I doing? Answering a post; the original poster was commenting about a VVR and said something about B+ being 350V, and not wanting to burn more $10 parts and mentioned rolling his own.

In my opinion the answer wouldn't be another $10 part that can handle 900 Volts and 14 amps. A $2 part would be more than adequate and if it burns again, not as big of a deal. Why do I think that? Well........
That quad of EL84s and preamp tubes in a liverpool will probably run right about 200mA max.
So parts that can handle 20x or 50x that, or 4 to 10 amps, I consider overkill, but at less than $2 it's not a big deal. Paying 5X the cost for a part that can handle 70x the max amperage.....ridiculous overkill.

I seriously doubt that even half the voltage would be dropped in this application, I don't think many people would go below 250V, however, lets say that it gets turned all the way down to 200V B+ for a reduction of 150V. That puts the part I suggested at merely 4X the total voltage drop (overkill), instead of 6X (ridiculous overkill).

4X voltage...Let me put it another way, would anyone buy 1400V caps for a 350V B+ supply? How about 2100V for 6X?

RdsON is 1.76 ohms for the 70W ST part, for a total of .352Volts lost when passing 200mA, while the NTE2973 is much better at .63 ohms, does the 0.126Volts lost really matter ? BTW the 150W ST is at 0.64 ohms.

And in the UNLIKELY event that this part has to drop 150V at 200mA then the power would be 30 Watts. Less than half the 70W part and 1/5 the 150W part (which is still less than $2) . So 5x the power dissipation for two bucks OR nearly 10x the power dissipation for ten bucks. On top of that, I'd bet that the amp gets run at 300V (or more) with only 10 Watts for the VVR to handle.
Sure crank up the temps at 30Watts, derate it by half, and even the 70W version costing $1.21 still works, (even if the beer on top of the amp would be boiling). I'd use a heat sink with either but if you decided to only use one for the ST part that would set you back anywhere from $2 down to twenty cents at mouser and currently at ApexJr a TO-220 heatsink is twelve cents. And with the price of gas, going to the local store versus shipping cost is a wash.

I'll take the 150W/650V/10 amp ST12NK60Z for $1.89 at Mouser in this case. Yeah, it's overkill for this application, but I'll spring for the extra 68 cents over the 70W version. Just my opinion. Sure beats the hell out of paying $10 for the NTE part, but YMMV.
Last edited by NEjoe on Sun Mar 27, 2011 5:26 am, edited 1 time in total.
Cliff Schecht
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Re: Mosfet VVR question

Post by Cliff Schecht »

You neglected to mention how heating will affect devices of different ratings. Choosing the part that is way overkill will have an easier time keeping cool under operating conditions, meaning RDSon will stay lower and you are less likely to run into thermal runaway issues. The smaller devices cannot handle as much standing current and so they will heat up faster, even if heatsinked to the chassis, compared to the way overrated part. Then you also have to consider how devices degrade over time under exhausting conditions. Again using the way overrated part is a (relatively) inexpensive way of guaranteeing a long operating life. A part rated at 30A is not meant to handle 30A continuously unless you have a way to get the heat out. And a chassis is by no means an optimal heatsink, especially when you consider the inside temperature of the chassis after a few hours of operation.
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UR12
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Re: Mosfet VVR question

Post by UR12 »

Nejoe

The part has to drop a lot more than 150v for example on an express running 400 volts the part VVR will limit 400 down to 40 s that's 360v and it is possible to take it all the way to zero if the installer saw fit. I have no idea where you are pulling these figures from.


I am not ashamed of any product I produce to sell and the facts are that the NTE part in this circuit has been extremely reliable. What few failures I have had I would chalk up to poor installations and not necessilary the part.


I give up as this has turned into a completely pointless discussion.
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Richie
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Re: Mosfet VVR question

Post by Richie »

maybe before you guys go boasting of the cheaper parts, try a bunch in some amps and see how they work.

I've installed quite a few,and the other cheaper overarted mosfets just seem to have weird problems like noise or something going on.
The NTE has worked fine. Yeah it may cost more, but alot less headache having to go through a bunch of cheaper brands that will vary from one to the next.
NEjoe
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Re: Mosfet VVR question

Post by NEjoe »

Are you saying it should be able to drop 360Volts on a 400V supply??

While I'm sure your kit can do that, I'm just unsure why anyone would.

But OK lets play that absolutely UNREALSTIC 360V drop times the current of two EL34s at 140mA. Wow, guess what, 0.28 Amps times 360V is about 100 Watts. Hmm, gee , my 150 Watt $2 part is still kicking (but probably not for very long without good heatsinks). Oh, and a 6V6 express (at only 90mA) would only run about 33 Watts, $2 parts still running just fine here.
But gee maybe I'll break out a 190W version for $2.53, or a 230W version for $4.37 and still be less than half the cost of an NTE part. If I'm really afraid of problems I could go all the way up to a 350W part for $6.59 (more spec for less money than NTE).

But rather than do any of that, I simply wouldn't take the plates under 200 Volts on an Express and keep the VVR power at 56Watts (even less for a 6V6 express at 18 Watts). Then the 150W at $2 is totally fine.

Is there someone out there that would really run the plates on an Express at 40 Volts????? Does anyone play at 40 Volts? what tone would you get? Could anyone post a sound clip, I'd like to hear it.
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Richie
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Re: Mosfet VVR question

Post by Richie »

Like anything, some things work, some don't,or some work better than others. Sounds like your going on whats on a spec sheet instead of trying many different ones in a real working amp. Use whatever you like.

And 360v is not unrealistic.

yes clips are everywhere.

Next i guess you'll be after the guys usign 2w pec pots for controls. Damn if that ain't over spec. Caps ,resistors,wire, The list could go on and on.

Dana has tried many different mosfets. The NTE [whoever makes that for them] seems to work the best with least problems.

So it may be overkill or more expensive, but it works without the problems the others that have been tried.
Yeah the others should work, but some of the lesser expensive ones do seem to have problems. When the same one or brand next one don't. Almost like picking a pretested preamp tube.
Instead of buying a pig in a poke.
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UR12
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Re: Mosfet VVR question

Post by UR12 »

NEjoe wrote:Are you saying it should be able to drop 360Volts on a 400V supply??

While I'm sure your kit can do that, I'm just unsure why anyone would.

But OK lets play that absolutely UNREALSTIC 360V drop times the current of two EL34s at 140mA. Wow, guess what, 0.28 Amps times 360V is about 100 Watts. Hmm, gee , my 150 Watt $2 part is still kicking (but probably not for very long without good heatsinks). Oh, and a 6V6 express (at only 90mA) would only run about 33 Watts, $2 parts still running just fine here.
But gee maybe I'll break out a 190W version for $2.53, or a 230W version for $4.37 and still be less than half the cost of an NTE part. If I'm really afraid of problems I could go all the way up to a 350W part for $6.59 (more spec for less money than NTE).

But rather than do any of that, I simply wouldn't take the plates under 200 Volts on an Express and keep the VVR power at 56Watts (even less for a 6V6 express at 18 Watts). Then the 150W at $2 is totally fine.

Is there someone out there that would really run the plates on an Express at 40 Volts????? Does anyone play at 40 Volts? what tone would you get? Could anyone post a sound clip, I'd like to hear it.
It is evident from your response that you don't have any idea what a VVR is or does. VVR stands for Variable Voltage Regulator. When installed in an amp it makes the B+ to either the power tubes or whole amp variable from full voltage down to 10%. So in an express it would give you a range of B+ from 400 down to 40v. This allows you to get cranked tones at lower volumes/power levels and yes all the way down to 40v on the power tubes or any or all of the amp you want. There are literally 100s and into the thousands of these being used in amps all around the planet with excellent results. There will be a loss of some tone at very low levels but it will allow you to play a normally rated amp at 35 watts at bedroom levels of say 1/2 - 1/4 watt. It is put to much better use in reducing levels from maybe 36 watts down to 15 or lower so the amp can be used in a number of venues instead of having to buy 2 different amps of different power levels. The speakers won't be pushing as much air at the lower power levels and this will be the biggest contributor of the loss of tone. Like I said, I have no idea where you are coming up with your voltages. The current rating on the mosfet has little to do with the grand scheme of things. Yea the one I use is rated at 14 amps and 900 volts but that doesn't mean that the device can operate at those extremes. It's total power dissipation is 275 watts. So if you were running the full 14 amps the voltage couldn't exceed 19.6 volts or you would be exceeding the devices power rating. By the same token if you were running 900v, the the device could only handle 300ma before it exceeded it's rating. In the Express if we have the full 400v across the mosfet you would be limited to 680 ma. Under normal circumstance you won't even come close to approaching that so the device is running well below it's rated 275 watts. Couple all that with fact that it's ratings will go down as the heat goes up. Then you have other instances or failures in an amp like a tube shorting out or a filter cap shorting out down stream that can cause a device to exceed it's rating. Or even the extra current flow when you first turn the amp on while the filter caps are charging. Personally I would much rather have a device that is over rated than a smaller rated device.

I have stated repeatedly that you can use any mosfet you want. I could really care less what anyone else uses. I just wanted to try and give the person considering rolling their own a few design parameters like RDSon voltage so that the current limiting would work properly, max power dissipation of the device so they werent dissipointed when there TO220 device couldn't handle the heat. The only problem that the OP had was that he didn't have a heatsink on his mosfet. That isn't the mosfet's fault or the VVR's design's fault. Unfortunately this turned into lets bash NTE and Dana. Personally I am sick of trying so you guys have the last word here cause I am done with this thread.
Last edited by UR12 on Sun Mar 27, 2011 5:28 pm, edited 1 time in total.
XgamerGt03
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Re: Mosfet VVR question

Post by XgamerGt03 »

If NTE works for you then so be it. There is no reason for anyone to get nasty here and it shouldn't be accepted here for that to happen.

I've done a VVR circuit with a number of IR and STM mosfets that work quite well. NTE is just way to expensive to me when I can get the same thing or better for half price usually.

The other thing to think about is that the 200+W rating for the MOSFET is usually crap anyway, many times the case can't handle more than 75-100W for long even if it has a heatsink.
Cliff Schecht
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Re: Mosfet VVR question

Post by Cliff Schecht »

I obviously have some disdain for NTE because I've been burned by them so many times. I used to buy parts from them at Fry's but I can't deal with overpriced dead parts that I can't return. FWIW I feel the same way about RS stuff.

Dana, I apologize for using such strong wording. I wasn't trying to directly attack you or your integrity. I've seen more than a few examples of you standing firmly by your products and that says enough to silence (most) critics.

I probably shouldn't be posting at 4:00AM after 12 hours of work, we saw what happened last time somebody posted grumpy (*looks at Reeltarded*).

But I still think you should be ordering those FET's for cheaper from Mouser! :P
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dynaman
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Re: Mosfet VVR question

Post by dynaman »

Cliff Schecht wrote:I obviously have some disdain for NTE because I've been burned by them so many times. I used to buy parts from them at Fry's but I can't deal with overpriced dead parts that I can't return. FWIW I feel the same way about RS stuff.

Dana, I apologize for using such strong wording. I wasn't trying to directly attack you or your integrity. I've seen more than a few examples of you standing firmly by your products and that says enough to silence (most) critics.

I probably shouldn't be posting at 4:00AM after 12 hours of work, we saw what happened last time somebody posted grumpy (*looks at Reeltarded*).

But I still think you should be ordering those FET's for cheaper from Mouser! :P
Haha, grumpy or not, Re(el)tarded makes the quirkiest and funniest posts around here.
Trout
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Re: Mosfet VVR question

Post by Trout »

Well,

Me, I'll stay in the over rated NTE camp on this one. I have played a Richter Supra-Luxe Pro that is equipped with the NTE and its rock solid. My understanding is she hits that thing with 475V. Its a 200ma PT so it is clearly in the upper range area.

Interestingly it does not even get warm after hours of use. 5-6 bucks for peace of mind seems meaningless when comparing the the limited life we get out of many new production tubes.

Has anyone tried any of the Fairchilds?
http://www.mouser.com/Search/ProductDet ... OZOA%3d%3d
flood
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Re: Mosfet VVR question

Post by flood »

at the risk of reviving a very dead thread: hi again to everybody from india. was on a hiatus from the amp hobby, and thought i should peek back here to solve my VVR problems, thinking i could get away with paralleling my MOSFETs.

I've been using IRF840Bs in my VVR installations, and none of them have lasted particularly long. things got embarrassing after a FET blew on an amp i built for somebody else. in any case, it's become pretty clear that i need to rethink my approach to power scaling using the IRF transistor.

Replacing the transistor is a real PITA - for this reason, I think I would spend the extra buck on the NTE part if it were available here. buying them in retail quantities from mouser, digikey et. al. is prohibitively expensive though.

i'd love to know if anybody has had any experiences with the fairchild HGTP10N120BN, and if major modifications to the basic circuit would be necessary to use it.

in general, i'm thinking about skipping power scaling altogether in the future because i generally use preamp gain when i play - which is fairly rare, since i've been too busy with regular work to breathe these days.

just my 2 cents/experiences to add some perspective here. thanks dana for your work and contributions to the community.
In the interest of full disclosure, I am Animal Factory Amplification.
Tillydog
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Re: Mosfet VVR question

Post by Tillydog »

flood wrote:I've been using IRF840Bs in my VVR installations, and none of them have lasted particularly long.
It would help to know voltages & current requirements of the circuits that you're building.

As long as you don't exceed the voltage rating of the IRF840, and it's adequately heat-sinked, it's hard to see how it could be killed by almost any conceivable VVR type application.
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