How can an amp with the same power tubes and PT but a different PT = more watts?

[catnine]

 I am confused . The Allen amps PT I have is listed in quite a few of his builds up to 35 watts with 6L6's , yet I have the same PT only mine has a higher HT voltage and 30mA more current rating and the only difference in a build he uses the PT i have and OT I have yet with 6V6's it 5 watts shy of the same amp only it has a different OT . mine is 7000 ohm to 8 ohm and the other is 6600 ohm to 8 ohm . And mine has the split load PI and the other has a LTPI . So my build not knowing his exact build spec is 15 watts and with a different OT and a LTPI the other is 20 watts and using 6L6's instead of 6V6's with the same trannies as described above one is 25 watts and the other is 35 watts.

 I know OT's are rated as to how much power they can handle. I can't say I understand how the ---- they work. 

 I bought the PT and OT in 2005 and used to run it with a pair of 6L6's as the PT and OT were rated to handle either 6V6's or 6L6's and it was louder and cleaner with 6L6's and thee PT drew more current so I could feel the PT ran a bit hotter but not where you could not keep your hand on it all day long. Plus I suspect 6L6's put out more heat than 6V6's do.

 How does one rate the output in watts on any amp? I have more PT and OT than a BF deluxe reverb yet it uses 6V6's and it is rated at 22 watts.

 Not that I care . what ever mine is watt wise with 6V6's it's pretty durn loud .

 All I recall because it's been so darn long is that to use the 6L6's I lowered the 1st dropping resister from 5k to 2.5k I did this because I was told the 6L6's needed more voltage and of course drew more current but I didn't have any problem using the 5K , it sounded the same and nothing got any warmer. I think it was because it was closer to a 5E5A with 6L6's without the added gain stage.

[PRR]

> OT's are rated as to how much power they can handle

"Cleanly" at low frequencies.

Use a loose definition of clean, or measure well up from low frequencies, you can pass a LOT more power. "10W" at 60Hz can pass nearly 100W at 180Hz.

> I am confused

Me too. You list several different amps, no information how the power rating was determined (1%THD at 80Hz? Maximum distorted midrange?).

If it's loud enuff, if you are not bidding for government work, be happy.

[HotBluePlates]

HBP has left the building.

[catnine]

> OT's are rated as to how much power they can handle

"Cleanly" at low frequencies.

Use a loose definition of clean, or measure well up from low frequencies, you can pass a LOT more power. "10W" at 60Hz can pass nearly 100W at 180Hz.

> I am confused

Me too. You list several different amps, no information how the power rating was determined (1%THD at 80Hz? Maximum distorted midrange?).

If it's loud enuff, if you are not bidding for government work, be happy.

 I don't have the the info on the tranny's I have . Allen Amps only lists the basics . There is info on the PT's but on the OT's it only lists the primary and secondary impedence of what tubes can be used. They are made to his specs by Heyboer. Yet Heyboer does not list them on their site.

[catnine]

And if you want to know how these things work, you should really read a book, new or old.

By asking how every component in an amp works, you're asking us to write a book topic by topic.

I know, that sounds like a jerk answer. I could give you a simple answer on tubes, PT, OT and watts, but that would be blowing smoke up your hind-quarters.

The book(s) should ideally talk about how a power supply, output transformer, output tube(s) and driver/phase inverter are all elements to be balanced to deliver power to a speaker. No one piece is the answer, it's how all work together.

There are easy ways to explain output section power, but if you're like me you refuse to grasp the easy way until you learn the hard way first. The "hard way" include all the little details of how things work, after which you find out it's simple and (for class A) pretty much boils down to ohm's law.

Problem is, I'm not certain you have a solid grip on ohm's law, so the logic of the easy explanation would probably not be obvious to you. That, and you've asked this same question in 8 different ways in many, many separate threads.

 I have a basic understanding of OHMs Law yet I have never had the need to use it enough for things to sink in. I certainly don't expect anyone to write a book for me . I have a few books , and there are websites that explain things that I have read ,aiken amps and valve wizard and yes ohms law comes into play. So when it comes to fender designs I get lost because I don't have the info of fenders tranny's to work from or even compare. Sure there are replacement tranny's for fender amps yet they are the new production replacements and still no specs other than basic stuff.

 I won't bring this up again. I will figure it out when I need to or if and when I reach that point. All I did was look at the tranny's Allen offered then called to make certain they would do the job I wanted yet they are not built off fender spec . I got the largest OT he had that worked with 6V6's and 6L6's and a PT that fit the chassis I had with enough power to do the job I wanted. I know a 20 watt amp will not be noticably louder than the 15 watt amp. Hopefully this all tells you where I am coming from . All I wanted to know was the basic idea of why one amp uses a larger OT than another and I realize 6v6's only put out some much and are biased in AB at say 70% and wondered how fenders BF deluxe reverb arrived at 22 watts. Yet I have no fender OT specs I can find to find out. Call it my own curiosity. I thought there may be a simple answer I can see there is not.

[Ed_Chambley]

I won't bring this up again. I will figure it out when I need to or if and when I reach that point.
[/quote]
No need to concern yourself on how many questions you post.  Anyone can answer you if they so desire.  I think the book comment was meant to request that you meet halfway by doing some reading and attempt to get your questions more specific.

The guys here have helped me a great deal and have gone to great lengths to explain a question, but when you have so many at once there is really no clear answer as all the components in you amp interact with each other and what is done in one circuit may act much differently in another.  This makes answering generic questions not possible.

Like asking "what OT should you use in a 50 watt amp"?  There are hundreds of possible answers, but if you ask what OT would you use if building a 50 marshall type amp and you plan to use EL34's, you will get some great answers.

So bring it up anytime as it is a forum and you are a member.  I don't really think anyone minds the questions, it is just difficult to answer when the question is not specific.

Also, most of the questions have been asked before, so I search and read the older posts.  There is some of the best, if not the best info on this forum of anywhere I have looked.

The guys here are great, so become a part

[Willabe]

Plus 1 to what Ed said.


            Brad       

[HotBluePlates]

HBP has left the building.

[HotBluePlates]

HBP has left the building.

[smackoj]

I read books about this stuff but when it gets to the 'sexy' parts like watching a Radio Spares OT get unwound, I start to blush and have to put it down....but seriously guys, I like the groovy math problems too, but I mostly live where the rubber hits the road, i.e. if it sounds good and doesn't exhale gaseous fumes or shoot sparks it's a keeper. Then, I play it for a couple days and then I make some changes within the common sense parameters and I play it some more. Sooner or later I get where I want to go in tone terms and all is right with the world. Here is a well used saying in closing, "the journey of a thousand miles starts with a single step"  

And I'm surely not going to write a book about transformers, but if MIT will give me an honorary Phd I could cut and paste together something they might enjoy? I'm joking so don't anyone get ruffled plz.

 

[catnine]

HotBluePlate :

 I am the one who should be sorry. I did look through the search on this forum but didn't find anything that explained this.

 Yes I have brought up this build a few times since 2009 I just don't recall asking how OT's relate to output in watt ratings and if I have perhaps my brain is going at 64. 

 Allen Amps are overkill that's why I picked them so I could fit the Princeton replacement he offers in the music master bass amp chassis I used to create this thing.

 The PT I got form him at that time was rated at 325-0-325 @180mA now it is lower on his site . You didn't have to take the time to go through all that trouble but I do appreciate it.

 So then if we stick with the 333V figure and the OT I got from him is 7000/2= 3500 ohm 333v/3500= 95 mA

 333v * 95mA = 31.6w peak

 31.6w * 0.7071 = 22.34 w

 I think the PT has enough current reserve not to sag .

I can use either a 5Y3 or GZ-34 rect since the PT only has a 2 amp 5 volt if I really want to ramp up the B+ with the GZ-34 but only if more B+ (plate) can be biased within reason with  JJ 6V6s .

 Thank you once again for your time explaining all of this to me. I didn't know the OT's impedance made the difference.

[HotBluePlates]

HBP has left the building.

[Ed_Chambley]

HotBluePlate :

 I am the one who should be sorry. I did look through the search on this forum but didn't find anything that explained this.

 Yes I have brought up this build a few times since 2009 I just don't recall asking how OT's relate to output in watt ratings and if I have perhaps my brain is going at 64. 

 Allen Amps are overkill that's why I picked them so I could fit the Princeton replacement he offers in the music master bass amp chassis I used to create this thing.

 The PT I got form him at that time was rated at 325-0-325 @180mA now it is lower on his site . You didn't have to take the time to go through all that trouble but I do appreciate it.

 So then if we stick with the 333V figure and the OT I got from him is 7000/2= 3500 ohm 333v/3500= 95 mA

 333v * 95mA = 31.6w peak

 31.6w * 0.7071 = 22.34 w

 I think the PT has enough current reserve not to sag .

I can use either a 5Y3 or GZ-34 rect since the PT only has a 2 amp 5 volt if I really want to ramp up the B+ with the GZ-34 but only if more B+ (plate) can be biased within reason with  JJ 6V6s .

 Thank you once again for your time explaining all of this to me. I didn't know the OT's impedance made the difference.

You can use a 5ar4 or GZ-34, but you may have to increase your dropping resistors if you would like to keep the preamp voltages where they need to be.  Also, in-between the 5y3 and GZ-34 is a 5v4.  The increased voltage to plate is 1.2 whereas the gz-34 is 1.3 and the 5y3 is 1.1.  Papa Bear, Mama Bear and baby bear.  Sometimes the 5v4 is just right.

[HotBluePlates]

HBP has left the building.

[catnine]

 The OT I got was a TO-25 and has been replaced by the TO-26 . I have to find the paper work that came with it . It was the only one he listed that detailed using 6V6's or 6L6's . Mine had different secondaries  4 and 8 ohm with 6V6's and 2 and 4 ohm with 6L6's . On the newer TO-26 he says this. " Also works great with a 2x6L6 or 2xEL34 amp (with 4 or 8 ohm speaker load) where the intention is to limit the output with core saturation for natural compression and sustain." So I guess the TO-26 with 6l6's limits output with core saturation perhaps meaning with the amp cranked up.

 I don't recall that statement with the TO-25 I got from him. I did email him and asked all he said was the TO-26 was designed to be more friendly with 8 ohm loads whether using 6V6's or 6L6's but there must be more to it than that, I'm just guessing here.

 I found the paper work for the TO-25 OT it does have a 7k primary to 4 or 8 ohm secondaries it weights 2.1 lbs and says it's a bolt in upgrade for Deluxe and princeton , 18 watt Marshall , 5E3 . it's deeper by 3/8" from the front to back that the other three .

 I also found the TP-25 PT sheet and it has the same specs as the one he has listed on his site and I recall calling him because I thought it was the stated 325-0-325 @180 mA and he said that there were numbers on the PT then he said they just changed over and I got the higher voltage model but the new data sheet . It states 120VAC line and 310-0-310 @150 mA on the sheet . I know I'm not drawing 150mA so i need to figure out my amps total mA draw but right now @ 118 VAC with all the tubes in I have 325 VAC on the secondaries before the rect tube. Odd thing is on my champ build using a weber PT rated at 330-0-330 @100mA  and the champ draws nowhere near 100mA I read 330 VAC before the rect tube all tubes in place. with 118 VAC line.

[catnine]

.

[/quote]
You can use a 5ar4 or GZ-34, but you may have to increase your dropping resistors if you would like to keep the preamp voltages where they need to be.  Also, in-between the 5y3 and GZ-34 is a 5v4.  The increased voltage to plate is 1.2 whereas the gz-34 is 1.3 and the 5y3 is 1.1.  Papa Bear, Mama Bear and baby bear.  Sometimes the 5v4 is just right.
[/quote]

 I have a 5V4 yet it's one hoffman sells so it's not a real 5V4 , it's got 4 pins and a small botton like the sovtek 5Y3 . I already have 415 B+ to 417B+ depending on the VAC line . I have the 6V6's biased at 18.5mA when  the line is 119.5 offering the 117VDC B+ . perhaps it's best to keep the 5Y3 in there. Come to think of it I have a sovtek 5Y3 in the amp now and from a real 5Y3 the voltage increased about 10 VDC . I only have one NOS 5Y3 in my SF Champ build , I dropped the NOS 5Y3 I had in this build. It's really difficult to get a proper read on voltages since the line here fluctuates from 117 to 120 VAC within any given 3 minutes. I write down a chart with all the voltage points in a row and monitor the line , even then it's hard to watch two DVOMs at once so I take the high and low and line and write each one down then make more sheets.

[HotBluePlates]

HBP has left the building.

[catnine]

I was searching and found this topic , found it interesting !
 http://www.el34world.com/Forum/index.php?topic=9301.0

 It was sort of what I was thinking when I built this amp .

 I used bigger iron just for this reason . I wasn't trying to use a AA1164 princeton , I was just thinking of a way to use either 6V6's or 6L6's .

 I just used the basic 5E3 and spliced the 6G2 input to a 6G2 tone stack to the V2 second gain and split load PI the 5E3 uses and changed from cathode bias to adj/fixed bias.

 Right now using the 5E3 dropping resisters 5k and 22K I have 254VDC or the PI plate and 208 VDC on the second gain plate and I used the 1.5K cathode bias resister on the PI instead of the 1K princetons use .

 here is the schematic
http://www.el34world.com/Forum/index.php?topic=14865.0

It was much louder and powerful with the 6L6's and a GZ-34 . The only thing I can't remember is when I changed the 5k dropper to a 2.5K thinking the 6L6's needed more voltage . I know I had the 2.5k in there and then at some point changed it back to the 5k and don't recall if I went back to the 6L6's with the 5K but I may have .

[catnine]

 "So I'll submit Allen has it a little wrong, in that power output limiting with that TO26 is not due to core saturation; it's because the primary impedance is too high to take advantage of the increased current capability of the 6L6. The 6L6 is our firehose, and the OT is the garden hose spigot. Since even if the 6L6 acts as a dead-short, it will not result in more power output than the 6V6 with that OT (and with this B+ voltage), power output is limited by the transformer impedance and probably doesn't get into core saturation.

All bets are off if you apply this OT to a much higher B+ that a 6V6 couldn't handle; in this case, the 6L6 will make more power output. But an easier choice is keep the same B+ and drop the OT primary impedance to allow the increased current the 6L6 can permit. Which is why you see 4kΩ primaries in Fender amps, which keep about the same B+ voltage between their 6V6 and 6L6 models.

So, reiterating what I keep saying: output power is a matter of a balance of PT voltage and current capabilities, the OT impedance (and core size), and the output tube characteristics."

 Well that would then explain this 
http://allenamps.com/hotfudge.php

 if you look at the top description the hot fudge 25 watts with 6L6's then scroll down to the transformer info you see the hot fudge with nuts uses a different OT and has 35 watts with 6L6's . I don't know the specs on the TO30D because it no longer exists yet it still uses both 6V6's and 6L6's so the primary can't be much different than the TO26 ,perhaps it is just enough to allow more power with both tube sets like maybe 6600 ohm .

[catnine]

I checked all over the net and didn't find any usefull info on the TO30D by allen . I did come across some forums talking about them . All I could find is it had 4 and 8 ohm taps . Then I come across a forum talking about a mission 5E3 and using 6L6's the fellow bought the amp used and was told if he wanted to use the 6V6's with the 6L6 OT he could use the 4 ohm tap to the 8 ohm speaker load . I can't say if it was the allen OT or if allen amps and mission use some of the same units but I never heard of using a 4 ohm tap to a 8 ohm speaker with 6V6's unless the primary to secondary allows this .

[HotBluePlates]

HBP has left the building.

[catnine]

The wayback machine ,thanks , shows how little I know about the internet .

 So I guess the TO25 I have 7k with 4 and 8 ohm with 6V6's then when I used the 6L6's I had a 2 and 4 ohm secondary which would reflect a 3.5K primary . I had to use two 8 ohms speakers in parallel to get the 4 ohm load . All I know is when I used the 6L6's the amp was much louder .

 Not that I need that much amp here . I had to plug my strats into the #2 input and just bring the vol up to 2 1/2 and it was loud so I gave up on that and went back to the 6V6's and one 8 ohm 12" speaker . Thought back then I would gig again , didn't happen , everyone moved back to Chicago.

[Willabe]

Thought back then I would gig again , didn't happen , everyone moved back to Chicago.

You live in the area? I live in McHenry Ill.


                 Brad     

[PRR]

> Convert from peak watts to RMS watts by multiplying by 0.7071

I think this is 0.5.

0.707 of voltage, and 0.707 of current, is 0.5 of Power.

27.6w * 0.5 = 14w (Princeton)
33.6w * 0.5 = 17w (Deluxe)

You've computed "hard clipping". THD will be over 1% before clipping. THD may not exceed 5% until somewhere past clipping. So the same amp could be rated 12W or 18W. Depending how honest the maker wants to be, *or* how it looks in the catalog (same power stage with more knobs/speakers at a higher price "should" claim higher power).

[catnine]

Thought back then I would gig again , didn't happen , everyone moved back to Chicago.

You live in the area? I live in McHenry Ill.


                 Brad     

 No I used to but moved to southern FL in 1976 and then to Los Angeles in 1980 and am still here. 4 years in FL was 4 years to many for me , bug city . Can't say I like it much here either , it used to be nice but since the mid 80's it became crowded and more crowded and now it's packed .

[catnine]

Well I went back in the wayback machine . Looked at allen amps so the OT I have is dated 5/1/04 the TO25 and the TP25 is dated 3/4/05 I got them both at the same time in 05 . so the TP25 rocks right on the border of the dates that I can bring up so the PT could be either 310-0-310@160 mA or 325-0-325 @ 150mA . If I trust the data sheets included with each then I have the 310-0-310 @ 160 mA. Not a big deal . The OT I have is described different and mine is 2.1 lbs and the later one I don't have is 1.6 lbs. same number but different.

 (The OT I have )
"Upgrade for Deluxes™ and Princetons™ (plus an excellent 18W Marshall output transformer) where speaker clearance may be an issue (oversized speaker installed, silverface amps, custom baffles). This is a "fatter" Deluxe Reverb™ style output transformer with 50% more lamination stack using M-6 grain-oriented low-loss steel with paper-bobbin and paper-layered interleaved windings. 7K ohm primary to 4/8 ohm secondary. 3-1/8" mounting centers will fit both Princetons™ and Deluxes™. 2-1/2" across the end bells, 2-1/4" tall and 2-11/16" deep. 2.1 lbs. Can be used with lower wattage 6L6 amps with 2/4 ohm speaker loads. Excellent choice for 5E3 and 18W Marshall projects!"

 (Then they changed it later before they dropped it and states)
" A beefier output transformer with 50% more core steel for Deluxe™, Deluxe Reverb™ and similar 2x6V6 based amps bolts right in with the standard 3-1/8" mounting centers (fits a Princeton™, too!) and has both 4 and 8 ohm taps for single and dual 8 ohm speaker configurations. Custom wound exclusively for Allen Amplification and made in the USA by Heyboer this unit features a special high performance core steel for maximum output and clean bass. 7,000 ohm primary to 4 or 8 ohms. Also works great with a 2x6L6 or 2xEL34 amp (with 2 or 4 ohm speaker load) where the intention is to limit the output with core saturation for natural compression and sustain. Low profile "fat" design to clear the speaker in combo amps. Excellent choice for 18W Marshall and similar 2xEL84 amps, too. Paper tube, paper-layered and specially interleaved windings, cool black oxide finish and 12" pretinned Unistrand leads for fast installation. Stainless-steel mounting hardware is included! 2-1/4"H by 2-1/2"W and 1.6lbs."

 Glad I got the older model OT. There is some difference between the two, don't know if I care for core saturation like the later model describes .

[catnine]

> Convert from peak watts to RMS watts by multiplying by 0.7071

I think this is 0.5.

0.707 of voltage, and 0.707 of current, is 0.5 of Power.

27.6w * 0.5 = 14w (Princeton)
33.6w * 0.5 = 17w (Deluxe)

You've computed "hard clipping". THD will be over 1% before clipping. THD may not exceed 5% until somewhere past clipping. So the same amp could be rated 12W or 18W. Depending how honest the maker wants to be, *or* how it looks in the catalog (same power stage with more knobs/speakers at a higher price "should" claim higher power).

Well if that's the case I can live with 18 watts . It's pretty loud as is. And if not I can always stuff it back into the taller cab I built and stick in the 6L6's and go with 2 speakers for 4 ohm load or stay with the 6V6's and go with two speakers with a 4 ohm load.

[HotBluePlates]

HBP has left the building.

[Ritchie200]

Man I like these threads!  I, for one, like the Barney approach!  Real world application with a reference to an actual amp makes it easy to understand for me.

HBP touched on this a little and I would like to add a little more.  Catnine, you mentioned you picked a particular tranny because it was overbuilt.  Like HBP said, you will get a build with a increased headroom and a wider freq response.  That might not be what you are looking for.  A lot of the mojo involved with the old amps were the general (seemingly endless) variety of parts that were available at the time of manufacture, including maybe slightly undersized trannys (whether by design or by bean counter).  Sag and saturation play a big sonic role.  Many of the amps I know and love were on the edge of a flameout like the Vox and the Major.  Yet nothing else sounds like them due to the fine line they are walking.  You build them safe and they sound different.

Lots to consider!  Depends on whether you want to reproduce or forge (somewhat) new ground.

MVHO Jim

[catnine]

... the TP25 rocks right on the border of the dates that I can bring up so the PT could be either 310-0-310@160 mA or 325-0-325 @ 150mA . ...

It would be funny if they are the exact same transformer, but a different way of writing the spec. I bet the 310-0-310v @ 160mA TP25 would output 325-0-325v, when you only pull 150mA from it.

Those aren't hard numbers unless you're drawing that full rated current from the PT; at lower current draw, the voltage rises.

Glad I got the older model OT. There is some difference between the two, don't know if I care for core saturation like the later model describes .

I think that is a mis-statement on Allen's part. As I explained earlier, The core is smaller and lighter probably because his OT manufacturer pointed out they could do the same job with a smaller core of different, better material. For an OT that was already enormously bigger than original, and given they are selling these for people assembling their own amps (or Fender copies), bringing the physical size down a little is probably desirable.

But again, we already went through the reasons a 6L6 won't output more power with a 7k primary, and it's not because of core saturation (which would require too-much power being passed to the OT). The 6L6 gets "compressed" (his words) cause the primary won't allow the power increase.

> Convert from peak watts to RMS watts by multiplying by 0.7071

I think this is 0.5.

0.707 of voltage, and 0.707 of current, is 0.5 of Power.

Yep, got ahead of myself. But what's a square-root of 2 between friends? 

 I do think the allen PT is the same one as the old old. Now the OT i got just stated a lower power using 6L6's not saturation . His old site when I got the tranny's and since the Ot I have is dirrerent pehaps I can push 25 watts out with 6L6's . All I know is they made a noticable difference when I used them over the 6V6's. I doesn't really matter as I said the amp has got plenty of bottom end and mids and stays clean like I  like it until the vol is at 7 . It's great for blues so I like it fine.

[catnine]

Man I like these threads!  I, for one, like the Barney approach!  Real world application with a reference to an actual amp makes it easy to understand for me.

HBP touched on this a little and I would like to add a little more.  Catnine, you mentioned you picked a particular tranny because it was overbuilt.  Like HBP said, you will get a build with a increased headroom and a wider freq response.  That might not be what you are looking for.  A lot of the mojo involved with the old amps were the general (seemingly endless) variety of parts that were available at the time of manufacture, including maybe slightly undersized trannys (whether by design or by bean counter).  Sag and saturation play a big sonic role.  Many of the amps I know and love were on the edge of a flameout like the Vox and the Major.  Yet nothing else sounds like them due to the fine line they are walking.  You build them safe and they sound different.

Lots to consider!  Depends on whether you want to reproduce or forge (somewhat) new ground.

MVHO Jim

 I like the sound of my amp fine . It has plenty of everything I want . It has clean headroom and great lows and the single tone control does it's job well. My build is just a tweaked brown princeton/deluxe and turned out just like I wanted it to.

[catnine]

 I haven't played this build in some time . Today I had a chance . I used to have a 30 watt weber silver bell in it with a 1 3/4" voice coil and a 40 oz ceramic mag . I was foolish and sold that speaker and got a weber SIG 12S alnico rated at 25 watts.

 I only use three strats that I built with original single coils .

 I can't recall how it sounded last time I played it but somehow it sounds different now. I have a 12ay7 preamp tube in it and a 12ax7 for the second gain and PI and 2 JJ 6V6s and a 5Y3 .

 I guess I never really cranked it up like today I really pushed it . I low end is there as are the mids and highs and to sigle tone pot works well .

 It seems when I did in and play single notes even the low E it doesn't break up at 7 but with chords it does. At 5 it just begins the break up and at 4 it does not break up at all . This is without the NFB loop. I have an added switch that adds the NFB loop and once switched in it does not break up until at 7 on the vol but with NFB in order to get the same vol level is like 5 without the NFB . Basically the switch removes the 25 uf bypass cap on the second gain stage and add's the 57K NFB resister same as a fender brown princeton 6G2 so the NFB tames the speaker cone movement .

 I suppose with this say 18watt built the 25 watt weber sig 12 S alnico will hold up but who knows . I used to run this build with 2 twelves ., the  silver bell and an eminence tonker both ceramic mags.  It didn't break up at all , in fact it was so loud then that I could not crank it past 2 1/2 .

 Can't say I care for the sig 12 s alnico's breakup it's sort of a tiny bit harsh not smooth although it's a lot smoother when cranked with the NFB in play. It's just sort of dissappointing in a way. Not to say it's not loud on 4 with no NFB because I was playing it in the bedroom so the bed and carpet do soak up the vol somewhat. I thought perhaps of putting it back in the tall cab I made for it and use the sig 12 on the bottom and the weber sig 10S ceramic on top but I sort of doubt this will change the breakup coming in and the sig 10 is pretty bright sounding . With both speakers it may be louder because of more air moved but the bright sig 10 may be to much bright.

 I never played a brown princeton or a BF Deluxe so I have no idea how they sound or when they breakup . I looked up the stock speakers they used and the Deluxe had an Oxford that seems to be rated at 23 watts but I don't think it was alnico I know the princeton was ceramic. Webers site touts a 12F150 25 or 50 watt 40 oz ceramic for the deluxe and a 10F150 40 oz ceramic for the princeton  both have 1 1/2" voice coils and the 25 or 50 watts , the 50 watt has a later breakup so they are like the speakers I (used) to have .

 I don't think the weber sig 12S alnico is broken in yet so perhaps when it does that may help . What a bummer , but then at 4 it does sound pretty great and is plenty loud so have to live with what I have , no way is $100 in the cards for one speaker.

 I  must say the Champ build did sound prety good with the added 25uf bypass cap and does not break up until 6 when driven hard even with that cheap jensen C10R it had some good bottom end .