Recording amp build

[Gareth81]

Hi Guys

I am looking at doing a new build for an upcoming recording project and I would like people's recommendations.
My favourite amp is the blackface fender twin reverb, but cranking one of those will be far far too loud for this. So I am looking for a build that will have what I like in the twin but at lower volumes. What sort of results will I get with a similar circuit to the twin / deluxe but using 6v6 or smaller powertubes, and a single 10" speaker? Any other options? What are the lowest wattage power tubes and how do they sound?

Regards
Gareth

[tubenit]

Given those parameters, I'd build a one channel Deluxe Reverb that is cathode biased and use a VVR on just the LTPI and power tubes.  

Use a PT that will support 6L6's &  then cathode bias with a 330 ohm resistor. With this set up, you can use 6L6's, 6V6's or even 6K6's. You'd have to experiment with the cathode cap on the power tubes. Try between 47uf to 220uf.

I'd stick with one 12" Jensen Re-issue or Weber 12F150 speaker.

You should be able to dial anything from around 23+ watts to 2 watts.

Editable SCH schematics are here:  http://www.el34world.com/Forum/index.php?topic=12934.new#new

There is also a VVR for fixed biased amps however it would not allow the vibrato option (I think?) & cathode bias VVR is easier.

With respect, Tubenit

[Willabe]

There is also a VVR for fixed biased amps however it would not allow the vibrato option (I think?) & cathode bias VVR is easier.

You can use VVR/Power Scaling with vibrato, but you have to VVR the vibrato tube also.


          Brad   

[HotBluePlates]

My favourite amp is the blackface fender twin reverb, but cranking one of those will be far far too loud for this. So I am looking for a build that will have what I like in the twin but at lower volumes.

What is it you like about a Twin Reverb? Are you needing to crank the amp to distortion? Have turned a Twin up that loud before (perhaps on stage)?

It's hard to make suggestions without knowing exactly what you want. And it's hard to fake the authority of a Twin Reverb (or the similar, 1x15" silverface Vibrasonic).

[Gareth81]

Yup, played many a cranked twin reverb. Best one I have played was a genuine bf belonging to Neil Finn at roundhead studios. I like the sound of it beginning to break. So about 4 on the volume with no master / flat out master.
I'm not so keen on the VVR approach. I was more thinking of taking the twin preamp and using a much smaller poweramp section through a low wattage speaker. Any thoughts as to a poweramp model? Is it just a case of cut and paste or no?

Regards
Gareth

[tubenit]

I'm not so keen on the VVR approach. I was more thinking of taking the twin preamp and using a much smaller poweramp section through a low wattage speaker. Any thoughts as to a poweramp model? Is it just a case of cut and paste or no?

What is it you don't like about VVR?  

It is an inexpensive and effective way of keeping high enough voltage on the preamp to match the Twin Reverb preamp volts while allowing lower voltage to the LTPI and power amp to run lower wattage tubes such as a 6K6  (or a 6V6 at lower volts).

Sounds like you're wanting a slightly cranked tone of an 80+ watt amp at closer to 8 watts for recording purposes?

What lower wattage power amp & power tubes were you thinking of that will have a Twin Reverbish tone?
I like ECL84 tubes and 6BM8 tubes (which are low wattage) but they will NOT come close to the tone of a 6L6 or
6V6 or 6K6, IMO.

A lower wattage speaker is NOT going to resolve your issue.

You could simply build a Princeton Reverb with 6L6's.

With respect, Tubenit

[HotBluePlates]

Tubenit's got a point.

*If* you need the volume of a Twin at some point later (and don't mind the heavy lifting!) then building a Twin and adding some way to reduce output stage power is a good option.

If, however, you'll likely never need the Twin's brute force, the blackface Pro Reverb is the same amp but with a pair of 6L6's instead of a quartet.

In general, all blackface Fender amps have a "family resemblance" and generally sound the same. A Princeton Reverb will still give good "Fender clean" in a small package if you don't turn it up past 5 or so. It won't feel the same to you while recording, and you might want a midrange knob and bright switch.

I'd suggest you look over all the "AB763" model amps, but also the AA1164 Princeton Reverb and AA764 VibroChamp. Skip the AA864 Bassman, which will only sound like a Twin if you rebuild the preamp to match the typical blackface topology and values (it will be mud, stock). The primary difference in the blackface amps is the number/type of output tubes (power output) and the number/size of speakers. You might want to lean towards 6L6's, but you don't have to.

The speakers you choose will make a huge difference in the character of the amp, especially for recording. The high-power handling 12" speakers do sound different than the 10" speakers typically used. The bigger voice coils and different cones change the response. And for what it's worth, there were special JBL speakers used in some Twins and in the Showman cabs (both noted for stellar clean, but sometimes bright sound).

[Gareth81]

Already have a twin reverb that I drag around (sf modded to bf) 

I may have misunderstood the VVR thing. Is it used to run the 6l6's at lower voltages or is it used to run different, low wattage tubes? It seems more sensible to build the amp to the desired wattage rather than scale down a larger amp after the fact. 

My idea for the lower wattage speaker is simple to match the speaker to the output, so the breakup of the speaker is matched - i.e. a regular twin reverb has 2 x 50W speakers, for the 80W of output. So for a 10W amp a single 15W speaker rather than a 50W which will never really get going.

What type of differences would I expect using ECL84 tubes and 6BM8 in the place of 6l6?
What about using a single ended poweramp section? A single 6v6?

Regards
Gareth

[tubenit]

What type of differences would I expect using ECL84 tubes and 6BM8 in the place of 6l6?
What about using a single ended poweramp section? A single 6v6?

The ECL84 & 6BM8 tubes break up pretty easily and will NOT get you headed towards a fender twin reverb thing.  Closer to cranked Marshall than clean Fender.

Going back to what I originally suggested ................  

The Twin Reverb, Pro Reverb, Super Reverb and Deluxe Reverb share some very similar topology and components.  The Deluxe Reverb is the smallest of the
"AB763" - ish  type amps.  Princeton Reverb does not use an LTPI.

So my thinking is take the smallest of the AB763-ish amps (which is the Deluxe Reverb)  BUT make it cathode biased using a 330 ohm resistor so that you can interchange a 6L6, 6V6 or 6K6 tube without rebiasing.  Those 3 tubes will give you 3 different tones.  This will allow the amp to be used well for gigging out ....playing in a bedroom ........... or recording in a studio.

I have a Tweed Overdrive that I can use 5881/6L6 in .................... OR ..................... 6V6GT .............OR ............. using a 5Y3 rectifier, I can also use a 6K6 tube in it.  

However, the TOS PT is 275-0-275.   You will need a PT that is closer to 340-0-340 or so (I think?).   In light of the higher voltage PT, then you will need the VVR on the LTPI & poweramp to run the lower wattage tubes.

So you could consider to use a VVR on just the LTPI and power amp to adjust the voltages down to the 6V6 and 6K6   while keeping the preamp in the higher voltages to preserve the AB763 preamp tone.  I think you'll need 180v-200v range on the plates of the preamp to get the cleaner Twin Reverb tone.  

Then  I'd use a Jensen speaker .............. maybe a C12Q (which I happen to like alot) or a C12N.  The Jensen speakers were used in alot of Fender amps.

It think you could get this type of amp design to "somewhat imitate" a Twin Reverb on the edge of breakup ................BUT it would be at something like 8-12 watts of power instead of the 80-100 watts of power.

You probably would not crank the amp volume knob past 4 or 5 to preserve the cleaner (on the edge of break up) tone.

I don't think you'll get an exact Twin Reverb tone doing this but I think it will head that direction and have good reverb and vibrato and a Fenderish tone.

Again, I am just saying this is how I would attempt it. It may or may not work out for you?

With respect,  Tubenit

[HotBluePlates]

I may have misunderstood the VVR thing. Is it used to run the 6l6's at lower voltages or is it used to run different, low wattage tubes? It seems more sensible to build the amp to the desired wattage rather than scale down a larger amp after the fact.

True, this would be the traditional approach. Basically, it's what I was doing when I amassed a sea of vintage amps; get the amp that does it's "thing" better than any other amp. Eventually, I pruned down to just a couple of copies that I built.

The VVR/power scale reduces the voltages applied to either the output tubes, or the entire amp, so that it behaves the same but makes less power. What you're saying is the sensible way, unless you'd like to own just an amp or two to cover many situations. London Power also makes a product taking the opposite approach, a Super Scaler which will take an amp like a tweed Champ and boost the output to 60w or more.

But I'm off-topic. You could use the power scale/VVR to lower the power capability temporarily of your Twin, and otherwise keep the same sound. I can't say that I'm one to recommend drilling the extra two holes in the chassis that the power scale controls would require.

My idea for the lower wattage speaker is simple to match the speaker to the output, so the breakup of the speaker is matched - i.e. a regular twin reverb has 2 x 50W speakers, for the 80W of output. So for a 10W amp a single 15W speaker rather than a 50W which will never really get going.

True, but the small speakers don't sound like the big ones. The differences in voice coil diameter, cone type/shape, etc., make it so the smaller/lower wattage speakers don't have the same response as the larger ones. Just look at the scads of 12" "Fender style" speaker WeberVST makes... And they're all a little different.

But F%$# it all! If you'd like a smaller amp with some breakup and a cool blackface sound, a Deluxe Reverb with a good Jensen copy will do it for you. It pays in my opinion to use something other than the reissue Jensen speakers.

NOTE: Funny.. I was typing while Tubenit posted. We concur, except I think Weber makes a better "Jensen" than Jensen does now. I say this as a person who has Jensen reissue speakers in one of my amps (but I've also owned a LOT of blackface Fenders over the years).

[tubenit]

Funny.. I was typing while Tubenit posted. We concur, except I think Weber makes a better "Jensen"

Good point @Weber speakers.  Check out the 12F150.

Reason we probably concur, is HBP is my amp building mentor & knows 100 times more about this stuff then I'll ever learn!  But I did pay attention to him.  He knows his stuff!
 

With respect, Tubenit

[Gareth81]

8 - 10 watts sounds great, Tubenit.

So how about a weber 12A100 speaker, 12" 15Watts, with 2 x 6k6 tubes for the output? I still don't understand why I would use VVR instead of just hardwiring the lower voltage to the 6k6 tubes? Is it just for versatility or is there something dynamic that the mosfet does?


Regards
Gareth

[Willabe]

I still don't understand why I would use VVR instead of just hardwiring the lower voltage to the 6k6 tubes? Is it just for versatility or is there something dynamic that the mosfet does?

IMHO, it is much more versatile. Both for output volume/sound db's, + being able to swap power tubes to lessen the output volume/tone.

Tubenet has posted more low watt builds with great tone/channel switching options than perhaps any one on this web site, or perhaps any other site, my words not his.

It's - VERY WELL - documented through the decades how many, if not most guitarist being recorded would use a small, low output amp to get - Big Sound - on tape.

Clapton recorded Layla with a Fender Champ with a 10" speaker and Allman, who played slide on the whole record, was recorded with one of the Gibson GA20 amps, push/pull pair of 6V6, maybe 15/16 watts.

This was/is a Big sound, at least to me.

IMHO, you don't need a high power output amp to get a great sound to your recording medium.

So you like and have played through a number of Fender Twins, OK, and you want to be able to record that same sound at "4" or so, But that's a live environment and it's very different when you go into a studio to nail the same "sound". It's two different world's.

Sorry my friend but, I think your chasing your tail - IF - you want to go with an --- 80+watt --- output build to record with.

The guys here can help you build a great -- "Recording" -- amp if you stick with it and work with them.


                      I wish you well on your new build,          Brad      



 

[Gareth81]

So you like and have played through a number of Fender Twins, OK, and you want to be able to record that same sound at "4" or so, But that's a live environment and it's very different when you go into a studio to nail the same "sound". It's two different world's.

More the other way round. I have recorded my twin, and others, lots of times. But for an upcoming project that kind of volume level won't be an option.

The issue is acutally less important when playing live than when recording, as there are too many variables. The house engineer can ask you to turn down, and that's that. I have a PPI master in my twin I use for live playing and that works well, but when I record it the master needs to be close to 3/4 full at least otherwise you may aswell use something else, deluxe or something.

I suppose the question could be rephrased as how to build a low wattage Reverb Deluxe, but a twin and a deluxe sound different and its the twin I like best so it makes the most sense to use that as reference when descibing what I want to do.

I probably don't need versatlity in the output section. The amp can stay as a recording amp. Is that the only reason for VVR?

Regards
Gareth

[tubenit]

The reason for the VVR is this .............................

How will you have 180-200v on all the preamp tubes AND something like 150-175v on 6V6's?

You could accomplish that by using two PT's on the same amp chassis ...........OR spend $30 for the VVR (which is not much bigger than a quarter).

You can always set and forget the VVR if you want ......... or mount it on the back of the chassis.

Even if you went hardwired with 250v on 6K6's, you'd be hard pressed to still get 200v on the V1a preamp.  Remember you've got reverb, vibrato, preamp and LTPI that have nodes on the B+rail.

The VVR is an inexpensive and effective way of lowering the voltage to the LTPI and power amp while keeping the preamp voltage higher 180-200v.  

WithOUT the higher preamp voltage ........... it will NOT sound AB763-ish baby Twin Reverb. The higher preamp volts are essential in keeping the clean tone, IMO.  

What is your reluctance in using a VVR?   Can you explain that, please?

There is an abundance of info on the VVR with cathode biased amps in the Hoffman ARCHIVES along with layouts, schematics and photos.

With respect, Tubenit

[tubenit]

 

but a twin and a deluxe sound different and its the twin I like best so it makes the most sense to use that as reference

Given that statement,  I don't know of an approach that will give you a low powered Twin Reverb sound?
I would anticipate my suggestion to sound more like a Deluxe Reverb at low volumes prior to breaking up. And that would be with the DR volume on maybe 4 & your guitar volume on 6 or less.

IF you hear a signficant enough difference between a DR (not cranked) and a Twin Reverb, then I would NOT attempt the idea I have suggested.  I'm not sure there is a tube amp design that will get you what you want?

With respect, Tubenit

[tubenit]

http://soundcloud.com/spetersonmusic/2011-12-fender-clean

That soundclip was done by an Axe-FXII with with some delay and the "Fender" setting.

Using something like that, you can get a reasonable Twin Reverb tone at extremelly low volume levels.

With respect, Tubenit

[Willabe]

More the other way round. I have recorded my twin, and others, lots of times. But for an upcoming project that kind of volume level won't be an option.

Your a lucky guy to have been able to record in a studio that can handle a Twin's volume. Must be nice.


                      Brad         

[HotBluePlates]

8 - 10 watts sounds great, Tubenit.

So how about a weber 12A100 speaker, 12" 15Watts, with 2 x 6k6 tubes for the output?

There are significant tonal differences among the various Fender-style 12" speakers Weber produces (just as there are with the original speakers).

If you want to mimic the Twin Reverb (and blackface tone in general), the best choice is the 12F150 and in a 25w rating and light dope for your application. If you're concerned you won't get quite enough speaker breakup and really want an alnico speaker, consider the 12A125S in the 20w rating and light dope.

Of course, you can always e-mail Weber for a recommendation. Be sure to be very detailed by saying you want to replicate a blackface Twin Reverb being pushed, but with a speaker matched to a 10-15w output section and with possibly a fair amount of speaker breakup.

I say this because I currently have ceramic Jensens in one tweed-style amp (one of the bigger ones) on purpose for a cleaner sound, while my tweed Deluxe copy has a smaller voice-coil alnico Weber for more speaker breakup. They definitely have very different characteristics, while both being Fender. But blackface Fender don't equal tweed Fender, in a number of respects.

I know you'll get a good product regardless; I'm simply offering suggestions based on the goal of "blackface Twin Reverb, but quieter."

[Gareth81]

The Fractal Audio Axe-FX II sounds good, only have pc speakers to listen on here on holidays, but sounds convincing to me.
I said twin reverb just because that's my frame of reference, but yes, I would expect the finished product to sound more like a Deluxe.
I regards to the VVR, this may seem like a stupid question, but I don't understand why you can't just use resistors to lower the voltages to the powertube and LTPI and retain the higher voltages on the preamp?
I will email weber and see what they say about a speaker recommendation and post it back here.

(Incidently, I have 2 x Weber Alnico Bluedog's in my gigging twin reverb, simply because I needed to replace the crappy 70's speakers and I already had these left over from a bluesbreaker type build - its a unique sound but not classic twin)

[tubenit]

I regards to the VVR, this may seem like a stupid question, but I don't understand why you can't just use resistors to lower the voltages to the powertube and LTPI and retain the higher voltages on the preamp?

Let me ask you two questions:

1)  Show me a schematic drawing of how you will use resistors to lower the powertube voltages to 140 volts from (let's say) a
     300-0-300 PT that has a 5V4 rectifier bumping the voltages up to 360v    while retaining  200v on the V1 plate?

     In your schematic, please show me the resistor value that you will use to reduce 360v from rectifier to 140v on the power tube plates.

2)  What is your concern about using a VVR?

With respect, Tubenit

[HotBluePlates]

I regards to the VVR, this may seem like a stupid question, but I don't understand why you can't just use resistors to lower the voltages to the powertube and LTPI and retain the higher voltages on the preamp?

Different way of thinking about it:

What if you have an amp and think to yourself, "my amp sounds great, but I really wish I could get the same sound it makes when I'm onstage at a club, but at bedroom/apartment volume level."

If you don't mind buying/building a 4w amp that makes the same sound as your 40-80w amp, then you build the small amp.

But for a very small fraction of the cost of another amp, you can add VVR/power scale to your existing amp to enable it to get its cool, loud tone at any volume level. It can be a 4w amp at one VVR setting, a 20w amp at a different VVR setting, and an 80w amp at a full-up VVR setting.

To many folks, that flexibility is more desirable than owning/carrying multiple amps.

[Gareth81]

Well that does sounds appealing if it achieves the same result. In terms of convenience, becuse the twin is so big and heavy, it would be easier to have one amp that stays in the recording room and another that lives at rehearsal / gigs. It would, however, be much cheaper not to build a new amp!

What are the tonal changes the power tubes exhibit when less volatge is applied, is it just lower wattage / earlier breakup or does the tone also lose body? Is this similar to "starved tube" designs? Surely it is better to run tubes at their optimal operation point rather than underpowering larger tubes?

Would it be best to use VVR only to run a different type of tube, 6k6 for example, pull the 4 6l6's and put in two 6k6's and turn  the VVR down? If so would you use a switch with some preset resistor values instead of a pot on the VVR unit?

Tubenit: I can tell from they way you've asked me that I must be wrong, but I would have thought increasing the 470 ohm resistor at the power tubes would lower the voltage without affecting V1. I'm not sure what the current draw would be at this point off the top of my head, but assuming it was 0.1A, V=IR says that a 2k2ohm would do it.
You'd also have to put in some form of attenuation from the phase inverter into the power tubes and perhaps some blocking diodes to isolate the two parts of the power sections? Do you need the mosfet to behave dynamically?

But I'm not an electrical engineer,  and I'm out of my depth! So, VVR it is....

[HotBluePlates]

What are the tonal changes the power tubes exhibit when less volatge is applied, is it just lower wattage / earlier breakup or does the tone also lose body? Is this similar to "starved tube" designs? Surely it is better to run tubes at their optimal operation point rather than underpowering larger tubes?

Would it be best to use VVR only to run a different type of tube, 6k6 for example, pull the 4 6l6's and put in two 6k6's and turn  the VVR down? If so would you use a switch with some preset resistor values instead of a pot on the VVR unit?

"VVR" = Variable Voltage Reduction => one maker's term for a pot-adjustable regulation method to lower the supply voltage to all, or part, of an amp.
"Power Scale" => another company's term for similar/same system.

Rather the me typing a long explanation of power scaling's effect on the output stage, read it from the source here and here.

An interesting note is that if you apply VVR/power scaling to the output tubes only, you need a master volume... to reduce distortion! In effect, reducing the plate and screen voltages simply makes the output stage operate as though it were capable of much less power output. The preamp makes as big a singal as it always did, but now the "smaller output stage" is more readily overloaded by the now-big preamp signal. The master volume is then used to reduce the drive signal from the preamp so that you can get any level of output stage distortion with any level of preamp distortion, from none to a lot.

The essential character of the output stage doesn't change, because the tube type used still has its same basic character. It's just that where it might have typically produced 80w before, with a low power scale setting, the same output section may only be capable of producing, say 10w. That is a function of the smaller plate voltage, and the smaller plate current (due to smaller screen voltage).

As we talk about it though, it seems like a smaller amp might be favored, simply because it's easier to transport to/from the recording venue than the Twin. If that's a big factor in your decision, please don't let me talk you out of a smaller, more portable amp.

EDIT: Linked Fixed

[Gareth81]

Well, I have a champ as a low wattage amp alternative, so I think you've convinced me to put a VVR in the twin. The first link you posted seems to be wrong? Would you mind reposting it?
With the master volume issue, would it be preferable to have a PPIMV that was linked to the VVR so the circuit was essentially always with the master on 10 but the power scaled down? What model PPIMV would you suggest?
The VVR website also says that the circuit is only suitable for amps up to 50W, will I need to use two for a twin reverb?

I have posted a new topic on the difference betwwen a convetered sf twin and a real bf twin, was gonna ask here but didn't want to go off topic 

[HotBluePlates]

Well, I have a champ as a low wattage amp alternative, so I think you've convinced me to put a VVR in the twin. The first link you posted seems to be wrong? Would you mind reposting it?
With the master volume issue, would it be preferable to have a PPIMV that was linked to the VVR so the circuit was essentially always with the master on 10 but the power scaled down? What model PPIMV would you suggest?

The VVR website also says that the circuit is only suitable for amps up to 50W, will I need to use two for a twin reverb?

Sorry, link fixed.

The usual approach is to power sclae only the output tubes; in that case, you'd use a PPIMV.

Since the VVR seems to be limited, order a power scale kit from London Power. It seems you already have a master volume, so no extra hole needed for that. You need a second mounting position for the power scale control itself, which is a large 2w pot. If you wind up with the London Power kit, instructions are already included for the master volume type to use.

Peruse London Power's website for details on their kits. I'm thinking you'll need the RBX kit and either SB-1 or SF-1.

The raw bias supply (RBX) kit is needed because of the method of incorporating a tracking bias supply; it will provide (most likely) ~120v of raw bias, which is then dialed down and controlled by the tracking bias supply and your amp's bias pot.

[tubenit]

I found this to be an interesting thread where Kevin O'Connor talks about Dana Hall's VVR.  My impression is that KOC seems to convey his Power Scaling is significantly "different" then VVR (on his website).   However,  he seems pretty upset about the similarity between VVR and Power Scaling.

http://www.powerscaling.com/phpbb3/viewtopic.php?f=10&t=1084

It was pointed out that 65-Amps has applied for a patent on their "master voltage". This is just Scaling despite what they wish to call it.
It has been suggested they based their circuit on Dana Hall's. Dana did not release his "known it forever, didn't copy Power Scaling" circuit until after the release of TUT4.

There are a lot of companies incorporating "master volumes that change the voltage in the amp". Some of these might have been from copying TUTs directly, but most would be from copying Dana Hall's theft of Power Scaling. Does this make them accomplices after the fact?

With respect, Tubenit

[HotBluePlates]

Well, he's right.

The VVR didn't exist until a number of years after O'Connor had already been writing about and selling power scaling amps and kits. There were a number of approaches tried for reducing volume output to push the output stage, but none was as original or well-implemented as the power scale circuit.

He's got a reason to be pissed. He has good grounds for an infringement/back royalty lawsuit, if he can find the money to hire the lawyers necessary to bring the case in 2 countries at once. The problem is, he very well may not have the money. Hopefully, he can find some very skilled representation that willing to get paid out of the settlement.

Here's a funny fact (not really): in these situations, you let the other guy go ahead and make as much money as he can from taking your idea. After the money has been made, then you bring the suit (and often net very much more than you would before the earnings from the infringement are known).

Rick James waited until MC Hammer made all the money he possibly could from "Can't Touch This" and then essentially took all that money.

[tubenit]

Reducing the power output of the power stage *without altering* how it handles signals is quite simple, and any approach used to achieve this IS Power Scaling. There are also simple ways to control power output which result in *alternate tones* as we dial down; these are simply "Variable Power".

I honestly was not aware that the VVR was "that similar" to the PowerScaling for there to be an issue of infringement?  Until I saw the comments of KOC today, I was under the impression that his power scaling was significantly different. Some of my impression that there were signficant differences  between the two were based on KOC's comments own comments.    So, his comment about "theft" of his idea took me by surprise.  NOTE that KOC himself makes a distinction between PS and VVR in the above quote.

IF KOC can come up with the idea, then I would think it would be possible for someone else to independently come up with a similar idea. Not saying that is the case here, just simply stating that would be possible.  For example, someone could hear of Power Scaling reducing the power output on the poweramp and then ponder ............ "how would I go about doing that?" .......... only to come up with a similar approach.

The reality is that most of what is new is built upon the foundations of what others have done, in my opinion.  

I think (?) that I have read portions of TUT 4 but I don't know if I ever saw a power scaling schematic?  At the time I thumbed thru TUT 4, I knew little to nothing about amps & electronics ........... so that kind of stuff was way over my head and my guess is that I never read about it or studied the schematic. Fortunately, I've learned alot and now I know "little to barely something" about this stuff.

With respect, Tubenit

[HotBluePlates]

It might be TUT4 that has the London Power Standard build project. That amp incorporates power scaling, as well as a number of other features. This is probably the basis his statement.

I don't know much about VVR. However, I have gotten one of KOC's power scaling kits before. By comparison, VVR looks like an attempt to do the exact same thing, but without as many protective features. I also haven't seen VVR with a tracking bias supply (although that may exist). There is a clever bit of engineering to make that bias supply work properly, and track changes made to the power scaled voltage without the need for rebiasing the output tubes (in fixed bias mode). Of course, with cathode bias, you don't need rebiasing regardless.

I'm just saying I'd never seen anyone else use an adjustable MOSFET regulator as a means of reducing power output, or controlling sag characteristics, until KOC made his power scale circuit available.

For what it's worth, super scaling (boosting the output power of a small amp) also uses a clever bit of engineering. The general approach might have been used in some other application in tube history, but I can't remember anyone advocating a similar approach that is so simple and effective. One version of Super Scaling was shown in maybe TUT4, again as a project to build.

The issue isn't whether an individual builds something for their personal use. You'll never run up against patent-related issues in such a case. The problem is when you take someone else's (or company's) product/innovation, call it you own and sell it for a profit.

[Willabe]

TUT5 has both the "Standard" and "Super Scaler", and is mostly a project book. TUT4 has the info/text/options on SC. I've wanted to build a SC for a long time. It is such a simple circuit that (if works as say's and at this point I think it does/will as advertised) will boost a Champ (or what ever) to 40w/50w with no change in tone. This is why I want to build one, to find out if I like it.  You can also chain them together in series to get more power. Also you can use multi tap secondaries back to back with a rotary switch for mismatch of power for volume changes +/- . He has put a ---lot --- of thought into this IMHO.  

TUT4 (chapter 3, 97 pages) and TUT 6 (chapter 1, 78 pages) have info on Power Scaling, --- lots --- of info, you'll have to see it to believe it, the --- thought --- he has put in PS. Every situation/need you could think of, it's in there. This alone to me, shows that Kevin came up with PS.

TUT4 (Sag, chapter 4, 24 pages) and TUT6 (Sustain, chapter 7, 18 pages) have info on his "Sag" by use of power mosfet (compression) and other ways to get this in an amp. Again, --- lots --- of thought put into this.

There was quite a bit of discussion at Kevin's PS site about Kevin's and Dana's method of bias tracking. I would go with HBP's thoughts on this.

IIRC, HBP's pointed out one time here that KOC's PS is fed from pulsating DCV and Dana's VVR is fed from filtered DCV and IIRC KOC said the reason for using pulsating DCV is it's much easier on the mosfet.

Kevin also used a heaver duty mosfet, and his later kits used 2 or 3 in series. He also used a 2w military spec pot for the first PS kit's, 500 dcv ark over to case? Latter kits could use any style/size pot.

IMHO, I think Kevin was really hurt by Dana. IIRC, he talked with Dana at least a few times by phone, and also had e-mail contact with him, to try to work it out. And I believe this FWIW.     

FWIW, I have hoped for a while now that a little more of KOC's ideas would be added to cross-pollinated the great ideas already here.

                 Thanks,      Brad