Once being in an audio recording studio I connected my bass guitar to a really High-End amplifier. It was used to monitor records. It had very flat and wide frequency response characteristics, and very low THD. Sounds from the big loudspeaker with huge woofer and 18 tweeters mounted on a carpeted base under tiny black net were heard as if it was a window to the studio... A technician inserted a jack in his pult, moved a control up...
But I was really disappointed. My guitar sounded flat, dim, colorless, and tasteless!
That time I understood that the guitar alone does not sound. What does sound, is the whole system, which includes a guitar, an amplifier, and a speaker with a cabinet.
Each component has own "character", it means each component distort sounds. The same amp with different speakers gives another sound. The same speakers with different amplifier give another sound.
Jensen speakers are not good speakers, Fender amps give big THD if to compare to modern amplifiers. But people like them... Why?
I think, the answer is simple. They like the music recorded by musicians who used such rigs. It would sound different, if they had modern rigs. And probably, those old famous rigs would be considered sounding ugly?
Significant part of a tube amplifier is output transformer. It is needed to match high impedance of tubes to low impedance of speakers. It carries significant powers in a wide frequency band. For guitar, the band must be from 80 Hz to 10 kHz at least, for bass guitar it must start from 40 Hz, for classic organ from 30 Hz, for Hi-End, which means "all band which an ear hears and wide" at least from 16 Hz.
However, high-end transformer may be used for guitar amplifier, if to consider a frequency band only. But it will give fewer distortions, so a sound will differ. It will be "poor", not so "rich" of specific harmonics and resonances.
Is it possible to use guitar transformer for Hi - End amplifier?
Probably, yes. But transformed made for guitar will give less power in Hi-End applications. And probably, more distortions, because cheap iron sometimes was considered as good for "rich" sound.
A first, it may be made on a core of thick plates, in such case eddy currents on higher frequencies will suck energy and turn it into a heat, pulling down an amplitude - frequency curve on higher frequences. A second, it may have lower permeability and lower induction of saturation. It means, more turns of windings will be required to work on lower frequencies. Also, higher coercive forces may cause more distortions.
I recently bought some surplus transformers made for guitar amplifiers and want to find optimal conditions for them to work in hi-fi tube amplifier. However, it will transfer less power because of smaller inductance. And, probably, will require deeper feedback to get good linearity and flat frequency response. The iron itself looks quite hi-fi, the main concern is inductivity. So, I am going to find what maximum power will be transferred through it on the frequency of 30 Hz (it is low enough for hi-fi) without significant distortions. To do so I am going to connect a resistive load to the output of amplifier made with the transformer, connect the audio generator to the input of the amplifier, and to find the highest possible voltage which will show saturation of the transformer's core.
Another way is to connect some light bulb (in our case 25 or 50W) in series with the secondary winding of the transformer, plug it into a power outlet through variac, increase voltage while waveform is still sinusoidal, measure amplitude of 60 Hz AC on the coil, and find the maximum power of the output signal, using the formula:
Pmax=A^2/( R*8 )
where A - amplitude of square pulses, R - impedance of a speaker that will be connected to the coil.
Maximum AC on 30 Hz will be half of maximum on 60 Hz. (1/2)^2=1/4
Also, maximum sinusoidal AC will be 1/sqrt (2) of the maximal amplitude. (1/sqrt (2))^2=1/2.
1/4*1/2=1/8
Os simpler, to measure size of pulses on the oscilloscope's screen, power them 2, and divide by 16.
It will be the absolute maximum power the transformer is capable of on the 30 Hz frequency, limited by unacceptable distortions.
Tomorrow I will experiment...
After that, I will figure out what tubes is better to use with transformers, what plate currents and voltage are optimal for them.