Smalles tube amp

[Surgeon]

Re: Smalles tube amp

you dont need less power you need a less efficient speaker, jensen has some that are around 95db which should calm things down quite a bit compared to your 103 db wizard

That's a good point of course... I used the wizard because that's the only speaker I had laying around and I didn't wanna spend more money on the cab...

 

[drpietrzak]

Re: Smalles tube amp

blackheart killer ant, it's 1 watt and i think(not sure) it's $100 for the head

Killer Ant! I love mine. It is a home killer box for sure. Find the right speaker for you is all. I love mine with a Swamp Thang, but I am not real Marshall.

 

[wanmei1]

Re: Smalles tube amp

you dont need less power you need a less efficient speaker, jensen has some that are around 95db which should calm things down quite a bit compared to your 103 db wizard

Nah !
Too expensive.
Changing the pre amp tubes ( even just V1 ) is cheaper.

 

[wanmei1]

Re: Smalles tube amp

Sorry ... it does not work like that at all. You are talking gain stage and all this does is change the preamp to output stage ratio of things. If this were true a Fender tweed Bassman would be a very quiet amp, much more quiet than a Marshall JTM45 which is basicially the same curcuit using three 12AX7s rahter than 2 12AY7s and 1 12AX7.

Myles this will in fact reduce the rms output if you go to a low enough value pre amp tube.

If an amp is designed around 12ax7's, as most are, then of course it does work.
It won't reduce the gain in the ratio of the gain percentage table, perhaps I should have elaborated, but it will and does reduce the oputput of an amp.

If a power tube needs an input of say X mv to produce full output and you only feed it 20 percent of Xmv then the power tube can't produce it's maximum power rating it may only produce 50 percent.

Turn the output of the pre amp via the gain control to say 1 and crank the master volume to 10.
The amp isn't very loud because it's not recieving enough gain from the pre amp for the output tubes to produce full output.
You are "starving " the power tubes of the required input voltage.

Substituting 12ax7's for 12au7's.... same deal.
There is not enough output from a 12au7 ( gain factor of 19 compared to 100) to supply the output tubes with enough voltage to produce full rated output.
The amp has maybe 50 percent of it's normal rms output.
There are some negatives to this.
Perhaps you could do some spdbl measurents on an amp using 12ax7's and substitute 12au7's then post the reduction in output rms results here.

 

[super rad stuff]

Re: Smalles tube amp

that's also true, IIRC correctly, math goes like this: adding +3db on speaker efficiency is like multiplying the wattage by 10, e.g. 10W amp through a 103db speaker is about as loud as 100W through 100db...
cheers

then will i have a 'bedroom' volume amp if i hook up my 100w head into some low db speakers?:naughty:

 

[wanmei1]

Re: Smalles tube amp

that's also true, IIRC correctly, math goes like this: adding +3db on speaker efficiency is like multiplying the wattage by 10, e.g. 10W amp through a 103db speaker is about as loud as 100W through 100db...
cheers

No that's not correct.
A 3db increase in speaker efficency is eqivalent to doubling the power output, not ten times the power output of an amp.
So a 10 watt amp into a 103 db speaker is equivalent to a 20 watt amp into a 100 db speaker.

 

[super rad stuff]

Re: Smalles tube amp

No that's not correct.
A 3db increase in speaker efficency is eqivalent to doubling the power output, not ten times the power output of an amp.
So a 10 watt amp into a 103 db speaker is equivalent to a 20 watt amp into a 100 db speaker.

so then say i run a 100w amp into 103 db speakers, but want something less efficient. would running the amp into 94 db speakers be about equivalent to a 12 1/2w amp at 103 db? btw sorry for the hijack, but the info's already on this thread!

 

[bancika]

Re: Smalles tube amp

Nah !
Too expensive.
Changing the pre amp tubes ( even just V1 ) is cheaper.

changing preamp tubes will usually not reduce the volume noticeably....will reduce gain / distortion though...

 

[bancika]

Re: Smalles tube amp

No that's not correct.
A 3db increase in speaker efficency is eqivalent to doubling the power output, not ten times the power output of an amp.
So a 10 watt amp into a 103 db speaker is equivalent to a 20 watt amp into a 100 db speaker.

I don't think that's correct.
For amp wattage it goes by log10, so 100W amp through the same speaker is only twice as loud as 10W amp
+3b on sensitivity means double the volume, right? So if you move from 100db to 103db that should be equivalent to multiplying a wattage by ten.

 

[super rad stuff]

Re: Smalles tube amp

I don't think that's correct.
For amp wattage it goes by log10, so 100W amp through the same speaker is only twice as loud as 10W amp
+3b on sensitivity means double the volume, right? So if you move from 100db to 103db that should be equivalent to multiplying a wattage by ten.

nah it goes like this: wattage x 2= +3 decibels, so if one amp is 50 watts at 100 decibels, then an amp at 100 watts will yield 103 decibels. there are many resources you can check this out on, http://eurotubes.com being the only one off the top of my head.

edit: direct link http://eurotubes.com/euro-y.htm

 

[bancika]

Re: Smalles tube amp

for this part I'm sure it's true:
For amp wattage it goes by log10, so 100W amp through the same speaker is only twice as loud as 10W amp
for the other I'm not...looks like +3db is equiv to twice the power...

 

[super rad stuff]

Re: Smalles tube amp

for this part I'm sure it's true:
For amp wattage it goes by log10, so 100W amp through the same speaker is only twice as loud as 10W amp

i'm not sure about that part but i'm sure you got that right

looks like +3db is equiv to twice the power...

that's the part i was trying to explain.

 

[wanmei1]

Re: Smalles tube amp

so then say i run a 100w amp into 103 db speakers, but want something less efficient. would running the amp into 94 db speakers be about equivalent to a 12 1/2w amp at 103 db? btw sorry for the hijack, but the info's already on this thread!

You got it !
The following diagram should make gain factor pretty clear.

 

[super rad stuff]

Re: Smalles tube amp

then once i get the cash, i will again have that awesome bedroom amp in my profile, but at bedroom levels!... i think?? whatever i'm putting my amp back upstairs as soon as i have some new speakers

 

[wanmei1]

Re: Smalles tube amp

I don't think that's correct.
For amp wattage it goes by log10, so 100W amp through the same speaker is only twice as loud as 10W amp
+3b on sensitivity means double the volume, right? So if you move from 100db to 103db that should be equivalent to multiplying a wattage by ten.

See diagram in my previous post.
Hopefully this explains it.

 

[wanmei1]

Re: Smalles tube amp

changing preamp tubes will usually not reduce the volume noticeably....will reduce gain / distortion though...

If the power amp sections power output tubes don't receive the minimum input voltage required to produce full power from the pre amp tubes then they cannot produce their maximum output.
If your amp uses 12ax7 pre amp tubes and you sub these for 12au7's there is not enough signal voltage produced to allow maximum output from the power tubes.
I have a Laney VC 30 in my lounge room that I bought as a home practice amp. It's cathode biased so it's extremely powerful, almost as loud as a some 100 watt amps that don't use cathode biasing in their design. There was no way I could run it flat out. I subbed the 12ax7's for 12au7's and that reduced the output by around 40 percent.
I then bought a set of power output tubes that were selected to produce 20 percent less output voltage than standard and these have further dropped the volume of the amp by another 20 percent.
Bottom line is a monster screamer of an amp has been tamed into a practice amp that produces half the volume that it did before.

 

[jeremy]

Re: Smalles tube amp

cathode biasing is actually less efficient than fixed bias and was originally used cause it is cheaper than fixed bias. it does have a different sound but it is by no means louder.

the chances that changing preamp tubes will lower the volume is really slim. youd have to have an amp that you could turn all the way up without getting any clipping. by changing from a 12ax7 to a 12au7 you are pulling more current for those triodes and possibly changing the bias point

 

[karpathion]

Re: Smalles tube amp

so the more speakers you add. does it increase for each speaker added. i know if you go from 2 speakers to 4 you gain about 2 or 3 more db's. so up the sensitivity of the speaker's to say 103 and it gains even more. so what your saying is my 15 watt amp ran into a 4x12 cab with 103db's speakers will make it sound like it's a 60 what amp?

 

[wanmei1]

Re: Smalles tube amp

cathode biasing is actually less efficient than fixed bias and was originally used cause it is cheaper than fixed bias. it does have a different sound but it is by no means louder.

the chances that changing preamp tubes will lower the volume is really slim. youd have to have an amp that you could turn all the way up without getting any clipping. by changing from a 12ax7 to a 12au7 you are pulling more current for those triodes and possibly changing the bias point

The power amp section is class A and it just screams. I guess it could scream even more if it were grid biased but how much pain can you take in a living room. I have trim pots fitted as well.
Why don't your try subbing 12ax7's for 12au7's in your practice amp and then report back here as to whether you think the drop in output volume is due to the bias point changing or due to the drop in voltage feeding the power tubes ?

 

[bancika]

Re: Smalles tube amp

so the more speakers you add. does it increase for each speaker added. i know if you go from 2 speakers to 4 you gain about 2 or 3 more db's. so up the sensitivity of the speaker's to say 103 and it gains even more. so what your saying is my 15 watt amp ran into a 4x12 cab with 103db's speakers will make it sound like it's a 60 what amp?

not really, don't forget that speakers have to share that power, so 1 speaker will get about 1/4 of those 15 watts