# Technical Questions and Discussion on the Cleanest Tube Amp Possible



## BadHiwatt (May 9, 2017)

First, I'm not an amp builder or tech. I'm just a dude who loves amps and technology. So, if I say something stupid, please be kind. 

I'm looking for a harmonically rich, clean tone at 105db @ 1m. Speaker combination and type would be 'stock' or manufacturer recommended. 

Would a quad of KT88 Parallel, single-ended, Class A amplifier produce the lowest amount of distortion? 

Here is my thinking:

No phase invertor to drive into distortion or to be unbalanced.
No crossover distortion because it is class A.
A quad of KT88 in class A should produce at least 40 watts (?)
As far as pre-amp, I would love to have the baxandall tone stack from the Jim Kelley FACS, but don't know enough about how that would add to, or increase, distortion. 

What does the hive-mind think about this?


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## Alan Small (Dec 30, 2019)

this will be an interesting thread...looking forward to learning with others thank you very much


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## Paul Running (Apr 12, 2020)

BadHiwatt said:


> Would a quad of KT88 Parallel, single-ended, Class A amplifier produce the lowest amount of distortion?


It can be accomplished however, to operate with minimum saturation on the transformers, it's going to take a lot of iron for the power supply and the output transformers.
The filaments alone will draw: 4 × 1.6A = 6.4A.
The KT88's will be drawing: Ia = 4 × 140mA = 560mA...half an amp DC in an output transformer demands a great deal of iron to prevent magnetic saturation...going to be a very heavy amp...but an interesting project.


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## Paul Running (Apr 12, 2020)

Here's the data sheet that I usually refer to:


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## BadHiwatt (May 9, 2017)

Paul Running said:


> It can be accomplished however, to operate with minimum saturation on the transformers, it's going to take a lot of iron for the power supply and the output transformers.
> The filaments alone will draw: 4 × 1.6A = 6.4A.
> The KT88's will be drawing: Ia = 4 × 140mA = 560mA...half an amp DC in an output transformer demands a great deal of iron to prevent magnetic saturation...going to be a very heavy amp...but an interesting project.


Do you build amps Paul?


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## Alan Small (Dec 30, 2019)

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## Alan Small (Dec 30, 2019)

Alan Small said:


> Kijiji - Buy, Sell & Save with Canada's #1 Local Classifieds
> 
> 
> Visit Kijiji Classifieds to buy, sell, or trade almost anything! New and used items, cars, real estate, jobs, services, vacation rentals and more virtually anywhere.
> ...


this monster prolly needs a dolly to haul it around😊


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## Paul Running (Apr 12, 2020)

BadHiwatt said:


> Do you build amps Paul?


I still build do a bit of building...mostly experimental. I am familiar with the KT88, many years ago I built a SE amp with this tube. They can run very clean...great for Bass applications and the audiophiles like them too.
Yes, Alan I believe that you are correct on that call for mobile support.


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## loudtubeamps (Feb 2, 2012)

I would imagine an SVT or Hiwatt 200 would get you very close.
Obviously a speaker with a high efficiency rating will help get you there but it may not necessarily have the most pleasing sonic qualities.


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## Yerffej (Feb 7, 2006)

Alan Small said:


> this monster prolly needs a dolly to haul it around😊


Although that trans looks HUGE, it is indeed spec'd for a 50 watt amp as the seller indicated. Here's a schem:


https://www.thetubestore.com/lib/thetubestore/schematics/Garnet/Garnet-LB200F-PRO-200.pdf



(same model code #6K3227)

I have had better luck running a separate filament transformer when that much heater current is called for


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## nonreverb (Sep 19, 2006)

loudtubeamps said:


> I would imagine an SVT or Hiwatt 200 would get you very close.
> Obviously a speaker with a high efficiency rating will help get you there but it may not necessarily have the most pleasing sonic qualities.


Indeed, the SVT ,Ultralinear Marshall Major or Fender 400PS would do the job.


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## Jerome (Dec 4, 2015)

Well you might want to look at a McIntosh 275 to get some ideas . Should be pretty clean sounding , add a preamp and go !









McIntosh MC275 Vacuum Tube Amplifier


The MC275 Vacuum Tube Amplifier has all the features to meet the needs of today’s music enthusiast while preserving the qualities that have made it the most revered McIntosh tube amplifier of all time.




www.mcintoshlabs.com


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## loudtubeamps (Feb 2, 2012)

@BadHiwatt ..........just curious as to your specific requirements for spl of 105 dB?


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## loudtubeamps (Feb 2, 2012)

nonreverb said:


> Indeed, the SVT ,Ultralinear Marshall Major or Fender 400PS would do the job.


I wonder how much air this puppy would push?




__





Google Image Result for http://i.imgur.com/2mgtR.jpg






images.app.goo.gl


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## oldjoat (Apr 4, 2019)

what ? I can't hear what you're saying ...


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## Paul Running (Apr 12, 2020)

loudtubeamps said:


> I wonder how much air this puppy would push?
> 
> 
> 
> ...


Enough to create a wind-chill factor on a cool day on stage.


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## gtrguy (Jul 6, 2006)

With a very efficient speaker you are not going to need a lot of power to get to 105dB. Theoretically an Eminence Swamp Thing 12" (102dB 1W/1m) with 2 watts input is going to get you there. It might help to explain what you're shooting for.


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## Kerry Brown (Mar 31, 2014)

Isn't the point of using a tube guitar amp to introduce some colour to the tone? If you really want super clean wouldn't a solid state amp work better? I'm guessing you don't really want super clean but you want a tube amp that colours the sound in a way you like. This way of thinking may make it easier to get the tone you are looking for.


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## nonreverb (Sep 19, 2006)

loudtubeamps said:


> I wonder how much air this puppy would push?
> 
> 
> 
> ...


That's just stoopid huge....


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## BadHiwatt (May 9, 2017)

loudtubeamps said:


> @BadHiwatt ..........just curious as to your specific requirements for spl of 105 dB?


It was a number louder than my home DB meter has ever recorded me playing with a drummer.


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## dtsaudio (Apr 15, 2009)

Kerry Brown said:


> Isn't the point of using a tube guitar amp to introduce some colour to the tone? If you really want super clean wouldn't a solid state amp work better


Tubes can certainly be made to be clean, but parallel single ended is not the way to go. It may be class A but distortion is actually higher than an equivalently powered push pull amp. Which by the way you can bias to class A also. Just ask Vox.
Push Pull tends to cancel nastys. You will also save a ton of money and weight on the output transformer. Also paralleling tubes is generally a recipe for disaster unless you really know what you are doing as far as mating the iron to the tubes.
The more tubes you parallel, the trickier it becomes.


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## tomee2 (Feb 27, 2017)

Wouldn't something like a Twin Reverb or a Traynor YGL3, with a pair of JBL E120s or other similar +100db/W speaker work? Or EV 12, G12H100, various Eminence as suggested.


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## Budda (May 29, 2007)

Question - do you want compression from the circuit?


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## RBlakeney (Mar 12, 2017)

I had one of the 80s fender bassman 70s and you could pretty well crank it without any breakup.


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## Alan Small (Dec 30, 2019)

Kijiji - Buy, Sell & Save with Canada's #1 Local Classifieds


Visit Kijiji Classifieds to buy, sell, or trade almost anything! New and used items, cars, real estate, jobs, services, vacation rentals and more virtually anywhere.




www.kijiji.ca





worth looking at this schematic maybe


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## loudtubeamps (Feb 2, 2012)

BadHiwatt said:


> It was a number louder than my home DB meter has ever recorded me playing with a drummer.


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## loudtubeamps (Feb 2, 2012)

I’m not a solid state user by any stretch but I will defend my Peavey Special 130 as one of the nicest and loudest combos , period. Dunno how they did it but it sounds harmonically rich, clear and very present.


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## RBlakeney (Mar 12, 2017)

the ultra linear fender bassman amps seem to pretty much go full out with out breaking up.


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## tomee2 (Feb 27, 2017)

loudtubeamps said:


> I not a solid state user by any stretch but I will defend my Peavey Special 130 as one of the nicest and loudest combos , period. Dunno how they did it but it sounds harmonically rich, clear and very present.


I agree. I really like mine and I certainly dont need it to go loud. There's 2 versions..
Does yours have the autotransformer output? 
I think those also have the bigger heat sink.


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## loudtubeamps (Feb 2, 2012)

tomee2 said:


> I agree. I really like mine and I certainly dont need it to go loud. There's 2 versions..
> Does yours have the autotransformer output?
> I think those also have the bigger heat sink.


To be honest...I dunno??
I’ll have to do some poking around.....there goes the rest of my morning!


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## tomee2 (Feb 27, 2017)

loudtubeamps said:


> To be honest...I dunno??
> I’ll have to do some poking around.....there goes the rest of my morning!


Look underneath, if there's a power and another transformer, that's the autotransformer - it's not inside the chassis. They used it on the Renown and a few other hi powered transistor amps.


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## loudtubeamps (Feb 2, 2012)

@tomee2 .....nope. 
Now I’ll have to poke around and find schematics for the model with the extra iron.
Cheers


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## Paul Running (Apr 12, 2020)

Is this it?


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## tomee2 (Feb 27, 2017)

loudtubeamps said:


> @tomee2 .....nope.
> Now I’ll have to poke around and find schematics for the model with the extra iron.
> Cheers
> View attachment 362872


Maybe I was thinking of the Renown? But I recall reading about the autotransformer on tdpri or someplace like that. 
I do see some 130s with larger heatsinks.

Nice speaker you have in there! That's got be pretty close to having an EV12 in there.


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## Paul Running (Apr 12, 2020)

Maybe a Peavey Auto-Match built into the amp.


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## loudtubeamps (Feb 2, 2012)

Paul Running said:


> Is this it?


@Paul Running Nope.....this one I believe...only difference is the balancing iron to allow a 4 and 8 ohm option.
I’ve seen a couple of 130’s after poking a round with the extra iron and noticeably larger sink.


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## loudtubeamps (Feb 2, 2012)

tomee2 said:


> Maybe I was thinking of the Renown? But I recall reading about the autotransformer on tdpri or someplace like that.
> I do see some 130s with larger heatsinks.
> 
> Nice speaker you have in there! That's got be pretty close to having an EV12 in there.


Just shy of 70 lbs....I love the ATC but ...... this is my hand after a short carry.
I have an eminence neo coming.....hopefully it will get me close sonically to the ATC and shave about 30 pounds off of the strap/handle.
If not , I’ll have to start eating more Wheaties


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## Paul Running (Apr 12, 2020)

Maybe some day, somebody will solve the equation for gravitational shielding and you won't need the Wheaties.


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## loudtubeamps (Feb 2, 2012)

tomee2 said:


> Maybe I was thinking of the Renown? But I recall reading about the autotransformer on tdpri or someplace like that.
> I do see some 130s with larger heatsinks.
> 
> Nice speaker you have in there! That's got be pretty close to having an EV12 in there.


Just shy of 70 lbs....I love the ATC but ......🤜 this is my hand after a short carry.
I have an eminence neo coming.....hopefully it will get me close sonically to the ATC and shave about 30 pounds off of the strap/handle.If not , I’ll have to start eating more Wheaties 💪


Paul Running said:


> Maybe some day, somebody will solve the equation for gravitational shielding and you won't need the Wheaties.


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## tomee2 (Feb 27, 2017)

loudtubeamps said:


> @tomee2 .....nope.
> Now I’ll have to poke around and find schematics for the model with the extra iron.
> Cheers
> View attachment 362872


I think I found it... it's the original Special, from around 81. It has the output matching transformer like the Renown.
This has a schematic for it.


Peavey Special output transformer ? - Music Electronics Forum



The Special 130 came next, then the Special 150, and Special 112.
But there are some Special 130s with bigger heatsinks. As if they ran out and just threw on Renown heatsinks. (Bandit used 2 output devices, Special used 4, and Renown 6. )


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## Paul Running (Apr 12, 2020)

Here's a recent thread on this forum that pertains to an amp that may be your ticket. Mr. Morris may entertain a substitute to KT88s.
NAD from the Morris machine!


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