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 Post subject: Newbie question regarding wattage in tube amps
PostPosted: Nov Sat 24, 2018 10:21 am 
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Hello everyone!

Forgive me if this isn't the right place to ask, but I might be having trouble understanding some simple context here. Having spent all day on google and reading I figured I would post here to ask for your advice/opinion.

So I currently have both, Class-A, a 5 watt tube guitar amplifier and also a single ended 8 watt stereo (also tube) amplifier. Maybe there is a context I still need to wrap my head around but I can't for the life of me understand why a guitar amp rated at 5 watts with 8 inch speaker is so much more powerful than a stereo one rated at 8 watts. The guitar amp literally hurts when playing at more than half volume (without distortion) and a stereo amplifier I can crank all the way up and it's not very loud at all. It almost feels like the volume dial stops but the amp has more to give...
The guitar amplifier is not a hybrid solid state amp, it has smaller power and output transformers than the stereo amp yet produces so much more sound!
Is there something special about guitar amplifiers that I do not know? Shouldn't the single ended stereo tube amplifier produce more sound/volume than the guitar amp?

Any advice much appreciated!


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 Post subject: Re: Newbie question regarding wattage in tube amps
PostPosted: Nov Sat 24, 2018 11:00 am 
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Be prepared to get an answer in pieces......

questions:
1. Which one has the more efficient speaker?

2. For each amp, is the rating for peak power or continuous?

3. Are both in good condition?

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 Post subject: Re: Newbie question regarding wattage in tube amps
PostPosted: Nov Sat 24, 2018 11:32 am 
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Joined: Jun Mon 26, 2017 12:39 am
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The guitar amp is 5 watt peak power. Stereo amp is 8 watts peak.. Bookshelf speakers sensitivity is 90db, I'm not sure about the sensitivity of the guitar amp speaker, both are in excellent condition..


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 Post subject: Re: Newbie question regarding wattage in tube amps
PostPosted: Nov Sat 24, 2018 1:06 pm 
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You've got it down to just one question!!!! ( while most of the ARF world was asleep)

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"Measure voltage, but THINK current." --anon.


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 Post subject: Re: Newbie question regarding wattage in tube amps
PostPosted: Nov Sat 24, 2018 1:33 pm 
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To me, comparing a guitar amp with a stereo (hi fi) amp is like comparing apples and oranges. Guitar amps are designed to make music while hi fi amps are designed to reproduce music. Things like input sensitivity, frequency response, distortion specs, circuit design, and, of course, speaker/enclosure performance all contribute to the differences that you are hearing. The difference in rated power levels (5 watts vs 8 watts) is a relatively minor contributor to the audio differences you are hearing.

What are you using as an input source when you compare the two amps?

Dave


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 Post subject: Re: Newbie question regarding wattage in tube amps
PostPosted: Nov Sat 24, 2018 2:32 pm 
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If the stereo amp is splitting those 8 watts over 2 speakers while the 5 watt amp is driving a single speaker that alone is going to make a difference.

Larry

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 Post subject: Re: Newbie question regarding wattage in tube amps
PostPosted: Nov Sat 24, 2018 3:35 pm 
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Also---if the guitar amp has NO negative feedback....and the stereo amp probably does have it....That will make a big difference.


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 Post subject: Re: Newbie question regarding wattage in tube amps
PostPosted: Nov Sat 24, 2018 11:53 pm 
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aris77 wrote:
The guitar amp is 5 watt peak power. Stereo amp is 8 watts peak.. Bookshelf speakers sensitivity is 90db, I'm not sure about the sensitivity of the guitar amp speaker, both are in excellent condition..


90db isn't exactly ideal for a lower-powered tube amp, that can certainly have an effect on volume output.

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 Post subject: Re: Newbie question regarding wattage in tube amps
PostPosted: Nov Sun 25, 2018 1:14 am 
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aris77 wrote:
Hello everyone!

Forgive me if this isn't the right place to ask, but I might be having trouble understanding some simple context here. Having spent all day on google and reading I figured I would post here to ask for your advice/opinion.

So I currently have both, Class-A, a 5 watt tube guitar amplifier and also a single ended 8 watt stereo (also tube) amplifier. Maybe there is a context I still need to wrap my head around but I can't for the life of me understand why a guitar amp rated at 5 watts with 8 inch speaker is so much more powerful than a stereo one rated at 8 watts. The guitar amp literally hurts when playing at more than half volume (without distortion) and a stereo amplifier I can crank all the way up and it's not very loud at all. It almost feels like the volume dial stops but the amp has more to give...
The guitar amplifier is not a hybrid solid state amp, it has smaller power and output transformers than the stereo amp yet produces so much more sound!
Is there something special about guitar amplifiers that I do not know? Shouldn't the single ended stereo tube amplifier produce more sound/volume than the guitar amp?

Any advice much appreciated!
As has already been stated there are a lot of factors to consider but I'd guess that two are the most likely. The first is speaker sensitivity. I.e SPL. For a given power input a 96 dB SPL speaker will sound almost twice as loud as a 90 dB SPL speaker. Guitar speakers typically have higher SPL than stereo speakers.

The second is the amplifier's input sensitivity. Over the years guitar amps have had basically similar input sensitivities (guitars haven't changed all that much) but the same cannot be said for 'stereo' sources. The old 'norm' was around 1.8 V at the input but over the years has dropped a lot due to the common use of battery powered devices, some of which have outputs down to 150 mV, or even less. If your amp expects the old 'norm', and your using modern devices to drive it, then it very well may be the case there isn't enough 'volume' adjustment to reach max power output.


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 Post subject: Re: Newbie question regarding wattage in tube amps
PostPosted: Nov Sun 25, 2018 10:41 pm 
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I will concur with speakers making a great deal of difference versus max power. Like the man said, alot of musical instrument speakers are rated 96 db efficiency or better, lot of hi fi speakers are well below that rating, as a compromise to better response range or distortion or such. Guitar amp is amplifying one instrument, whereas a hi fi amp reproducing a whole spectrum of music is putting out power over all the frequency range, especially power sucking deep bass. But without seeing the particulars in each instance, it is not easy to give more info.

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 Post subject: Re: Newbie question regarding wattage in tube amps
PostPosted: Nov Mon 26, 2018 4:16 am 
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wazz wrote:
I will concur with speakers making a great deal of difference versus max power. Like the man said, alot of musical instrument speakers are rated 96 db efficiency or better, lot of hi fi speakers are well below that rating, as a compromise to better response range or distortion or such. Guitar amp is amplifying one instrument, whereas a hi fi amp reproducing a whole spectrum of music is putting out power over all the frequency range, especially power sucking deep bass. But without seeing the particulars in each instance, it is not easy to give more info.
Don't underestimate input signal voltage. A 10 to 1 voltage ratio comes out to a 20 dB loss of volume. I don't know what he's using but even a halving of signal voltage is -6 dB.


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 Post subject: Re: Newbie question regarding wattage in tube amps
PostPosted: Nov Mon 26, 2018 6:42 pm 
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Joined: Aug Wed 24, 2011 4:35 am
Posts: 4428
Location: Sunnyvale CA
aris77 wrote:
Hello everyone!

Forgive me if this isn't the right place to ask, but I might be having trouble understanding some simple context here. Having spent all day on google and reading I figured I would post here to ask for your advice/opinion.

So I currently have both, Class-A, a 5 watt tube guitar amplifier and also a single ended 8 watt stereo (also tube) amplifier. Maybe there is a context I still need to wrap my head around but I can't for the life of me understand why a guitar amp rated at 5 watts with 8 inch speaker is so much more powerful than a stereo one rated at 8 watts. The guitar amp literally hurts when playing at more than half volume (without distortion) and a stereo amplifier I can crank all the way up and it's not very loud at all. It almost feels like the volume dial stops but the amp has more to give...
The guitar amplifier is not a hybrid solid state amp, it has smaller power and output transformers than the stereo amp yet produces so much more sound!
Is there something special about guitar amplifiers that I do not know? Shouldn't the single ended stereo tube amplifier produce more sound/volume than the guitar amp?

Any advice much appreciated!


Are you sure that you are driving both amplifiers to capacity? Maybe your input signal level on the stereo amplifier isn't big enough to get all 8 watts out of it.

Brett


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 Post subject: Re: Newbie question regarding wattage in tube amps
PostPosted: Nov Tue 27, 2018 5:03 am 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 11420
Location: Powell River BC Canada
If you have a way to make a tone signal to feed your amplifiers/ speakers,
you can measure the sound level they produce with this inexpensive meter.

Or if you have, or can find. an old cassette recorder, you can make your own
that uses your DVM.
Attachment:
Radio Shack Sound Level Meter.jpg
Radio Shack Sound Level Meter.jpg [ 52.12 KiB | Viewed 967 times ]

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 Post subject: Re: Newbie question regarding wattage in tube amps
PostPosted: Nov Tue 27, 2018 6:07 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4242
Location: Boston, MA USA
As noted by others your problem is insufficient voltage gain on the part of the stereo amplifier. Guitar amplifiers have very high gain because guitars produce very low voltage, on the order of tens of millivolts. Stereo amplifiers have high gain only on their magnetic phono inputs. If you are using the ordinary high-level AUX or Tuner/CD input it requires several hundred millivolts. Your source may not have nearly enough output voltage to drive the stereo amplifier to its full output whereas it may be fine for a high-gain guitar amplifier.

-David


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 Post subject: Re: Newbie question regarding wattage in tube amps
PostPosted: Nov Fri 30, 2018 1:09 am 
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A high fi stereo amplifier is expected to be reasonably free of harmonic distortion from 20-20,000 hz, a guitar amplifier is run from a fairly narrow band of frequencies. They sound "better" when pushed hard and well into heavy distortion, depending on what you're playing anyway.


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 Post subject: Re: Newbie question regarding wattage in tube amps
PostPosted: Dec Sat 01, 2018 5:05 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Cortez, Colorado
To get 8 watts out of a single ended tube, you're gonna need something like a KT88 or GU50. I don't think even a EL34 can put out 8 watts SE with feedback. What are the stereo's output tubes?


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 Post subject: Re: Newbie question regarding wattage in tube amps
PostPosted: Dec Sat 01, 2018 5:20 am 
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Tin Omen wrote:
To get 8 watts out of a single ended tube, you're gonna need something like a KT88 or GU50. I don't think even a EL34 can put out 8 watts SE with feedback. What are the stereo's output tubes?
Feedback needs more gain (to use for the feedback) but has nothing to do with power output.

An EL34 can easily do 8 Watt SE. In fact, the Phillips datasheet says 11 Watt at 250 V plate and a 15k OPT. With an 18k OPT it's rated 8 Watt.


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 Post subject: Re: Newbie question regarding wattage in tube amps
PostPosted: Dec Sat 01, 2018 3:57 pm 
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Maybe his SE stereo amp is actually 4 watts/channel.

Dave


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