Anyone ever tried Power Scaling?

[ZachM]

Hey everyone, I was wondering if anybody has had experience with power scaling in your tube amps, something like this:

http://www.londonpower.com/pscaling.htm

It seems like an ideal solution for the "big power tube overdrive" crowd, and I for one would love to be able to get that sound without getting fired and/or arrested. I know that Reeves offers it as an option on some of their amps, and it may be more of a guitar system, but it sure seems like a great idea if it works. Has anyone had any experience with a system like this or installed it on your amp?

Thanks!

[billfitzmaurice]

Originally Posted by ZachM

Hey everyone, I was wondering if anybody has had experience with power scaling in your tube amps, something like this:

http://www.londonpower.com/pscaling.htm

This is nothing new, similar devices have existed for at least 30 years. They're mainly of value to guitar players.

[fu22ba55]

Originally Posted by billfitzmaurice

This is nothing new, similar devices have existed for at least 30 years. They're mainly of value to guitar players.

+1

I think it's a viable idea for cuddly little 50-watt guitar amps, but once you're talking about 200W or 300W all-tube bass amps, your more likely to make a shrinky-dink out of the power scaler's PCB than get any use out of them.

I have a 100W tube amp, a 200W tube amp, and a 300W tube amp. THAT'S power scaling.

[JimmyM]

that kind of stuff doesn't usually work with tube bass amps because they produce more power than these types of devices can handle. i noticed london power only offers amps that go 25w, and i see reeves only offers it on their guitar amps that are 30w or under. so that means it might work on a b-15, but that's about it.

[KramerBassFan]

Originally Posted by fu22ba55

I have a 100W tube amp, a 200W tube amp, and a 300W tube amp. THAT'S power scaling.

+1

Thats the way to do it.

If you want grind, get a 50w tube amp and use it for bass.

Putting a big device like that on a 300w SVT is just expensive, and asking for trouble.

[ZachM]

Cool, thanks for the answers guys. I had an inkling that big bass amps may be a little too much for a system like this, similar to the way that those hot plate attenuators can't really handle bass tube amp voltages either. But you never know until you ask!

Now to another question then...

Could you accomplish power scaling effectively by installing a system which would cut out pairs of power tubes? As in (using an SVT as an example) cutting 2 tubes from the output circuit, then 4?

I know that this will not get the same kind of saturation exactly, as a small amp (no OT saturation, etc), but would it get you somewhere or just put stress on the amp? I've not really heard of people doing this either, but is this a more viable option?

Originally Posted by KramerBassFan

+1

If you want grind, get a 50w tube amp and use it for bass.

I know this is ultimately the best answer, but out of pure curiosity what do you think?

Thanks again TB'ers.

[JimmyM]

it'll change the impedance the output transformer sees which could lead to early failure of it, and it ain't cheap to replace. best thing is if you want tube od at lower volumes, get a lower powered amp. don't **** with an svt. there's lots of scary stuff in there

[BassmanPaul]

IIRC the device is basically a high voltage MOSFET used to drop the B+ voltage to the output stage. This, of course, drops the available voltage that the output stage can swing reducing the power available at the speaker terminals. It's like a stabilized power supply with a variable output voltage.

[KramerBassFan]

+1

Just get a cheap 50w guitar amp.

It will be much cheaper than having to replace your SVT or DR201 when you blow up something.

There are thousands of little 50w or less guitar amps out there, like peaveys, marshalls, etc. Just get one, and hook it up to your bass cab, and dime it.

My opinion? This is a perfect opportunity to buy a load of amps.

[ZachM]

Originally Posted by KramerBassFan

My opinion? This is a perfect opportunity to buy a load of amps.

I can get behind this

[KramerBassFan]

I already have. With more one the way right now........

[Passinwind]

Originally Posted by BassmanPaul

IIRC the device is basically a high voltage MOSFET used to drop the B+ voltage to the output stage. This, of course, drops the available voltage that the output stage can swing reducing the power available at the speaker terminals. It's like a stabilized power supply with a variable output voltage.

Correct. It'll work just fine with a high power amp within the constraints posed by the tubes' characteristic and load line curves(he had it as an option in a 200 watt design at one time), but whether you'll like the results is another question. I've never bothered to build one because I flat out don't like tube amps for bass in my personal playing situations.

The OP could ping the folks at Maven Peal amps, who had the best implementation of the idea that I've encountered. Their claim to fame was a variable sag control, FWIW. Makes more sense to me than just raw power scaling.

Kramer's got the right idea IMO, just buy what you actually want/need.

[anderbass]

Originally Posted by ZachM

Now to another question then...

Could you accomplish power scaling effectively by installing a system which would cut out pairs of power tubes? As in (using an SVT as an example) cutting 2 tubes from the output circuit, then 4?

I know that this will not get the same kind of saturation exactly, as a small amp (no OT saturation, etc), but would it get you somewhere or just put stress on the amp? I've not really heard of people doing this either, but is this a more viable option?



I know this is ultimately the best answer, but out of pure curiosity what do you think?

Thanks again TB'ers.

The SVT is not a good candidate but I did this type of mod to my Mesa 400+ several years ago and Its still working great with the same tubes and no issues. More Info here: SWITCHABLE MAX OUTPUT MOD, FOR a 300/w TUBE AMP.

[ZachM]

Originally Posted by anderbass

The SVT is not a good candidate but I did this type of mod to my Mesa 400+ several years ago and Its still working great with the same tubes and no issues. More Info here: SWITCHABLE MAX OUTPUT MOD, FOR a 300/w TUBE AMP.

Hey thanks for posting! Your thread is actually what I was thinking of when I posted, but I couldn't remember the title or where I had seen it. This is very clever.

[seamonkey]

This doesn't address the commonly mentioned postulate that output transformer saturation has something to do with the tube sound.
Does it or doesn't it?

[ZachM]

Originally Posted by seamonkey

This doesn't address the commonly mentioned postulate that output transformer saturation has something to do with the tube sound.
Does it or doesn't it?

I think it probably does matter, and up the page a little, I did mention that I knew that the output transformer saturation would not happen with the "tube de-activation" system. So in that sense, I guess it wouldn't really get the full picture of what happens when you saturate a true low wattage tube amp. I'm just sort of postulating ideas that I think are interesting and/or may have some application. And who knows, it may still be a totally usable and awesome sound, regardless of whether OT saturation happens or not.

As somebody else said, really the best possible way to do power scaling the right way is to have a small amp. But I do think that built in power scaling is an interesting idea that has unique potential in it's own right.

anderbass, out of curiosity, why is an SVT an unsuitable candidate for your mod? From reading your thread, there are posts that say that your mod is suitable for any tube amp with four output tubes, so have you had an experience that makes you think otherwise?

Thanks again.

[JimmyM]

an svt is a perfect amp as it is. that's why

[anderbass]

Originally Posted by ZachM

Hey thanks for posting! Your thread is actually what I was thinking of when I posted, but I couldn't remember the title or where I had seen it. This is very clever.

Your welcome and thanks

Originally Posted by seamonkey

This doesn't address the commonly mentioned postulate that output transformer saturation has something to do with the tube sound.
Does it or doesn't it?

I'd never even considered how output transformer saturation affected the results of my mod, but that's a good point it probably does. My 400+ running at the 50 watt setting does seem to have more clean headroom than a couple of my other 50/80 watt all tube heads.

I dont use my modded 400+ at the lower output lift-switch settings to get full on saturated distortion, just to get that full woody tone with a nice bouncy feel at lower volume levels. And for that purpose my mod was a total success.

Originally Posted by ZachM

I think it probably does matter, and up the page a little, I did mention that I knew that the output transformer saturation would not happen with the "tube de-activation" system. So in that sense, I guess it wouldn't really get the full picture of what happens when you saturate a true low wattage tube amp. I'm just sort of postulating ideas that I think are interesting and/or may have some application. And who knows, it may still be a totally usable and awesome sound, regardless of whether OT saturation happens or not.

As somebody else said, really the best possible way to do power scaling the right way is to have a small amp. But I do think that built in power scaling is an interesting idea that has unique potential in it's own right.

anderbass, out of curiosity, why is an SVT an unsuitable candidate for your mod? From reading your thread, there are posts that say that your mod is suitable for any tube amp with four output tubes, so have you had an experience that makes you think otherwise?

Thanks again.

As far as I know nobody has ever tried a cathode-lift mod with an SVT, but we speculated the higher voltages the SVT power tubes run at would make this mod way more risky than with my Mesa. I wouldnt try this mod with my SVT's, but I'd sure like to see someone else pull it off.

Originally Posted by JimmyM

an svt is a perfect amp as it is. that's why

...

[JimmyM]

i think i figured out why...the mesa has 12 tubes arranged in push pull pairs. the svt has triplets instead of pairs and they're arranged as aaa bbb for their push pull operation instead of ab ab ab like the mesa. i'm not sure exactly why, but something about that configuration makes them unadaptable to removing tubes.

[teemuk]

There was a user adjustable B+ voltage regulator (or should I say "power scaling") circuit in the Ampeg's SVTxPRO hybrids long before Kevin O'Connor even wrote about it. I think even the newest hybrid model in that series still has one.