BASS OUTPUT TRANSFORMERS:
4 x 6L6, 4 x EL34, 4 x KT88/6550 etc.
EL34, KT88, 6L6,etc.
For Organ and other keyboard use bass or HiFi transformers.
For high quality PA power amplifiers use HiFi transformers.
It is substantially that the transformers used for bass is indeed designed and made exclusively for the purpose of bass guitar.
Bass instruments are not the same as a guitar. All though many manufacturers consider the output transformers as basically the same, they ought not do so.
Firstly the E-string on a bass are an whole octave deeper than the low E-string on a guitar. That is a 40Hz tone from the bass compared to a 80Hz tone from the guitar.
In the frequency domain the square law rules from the power point of view. This means that the bass output transformer must be build to handle 4 times the power (400%) of a guitar output transformer.
Just as the strings of a bass needs to be thicker than those of a guitar, so the bass transformer requires its own specific weight and size. In other words the core of a bass transformer must be notably larger than the core used to make guitar transformers and also, it must be wound for higher induction.
Secondly a bass is usually not cranked or played continuously into overdrive. The bass tones must remain deep, rock solid and full bodied at all levels. Ask your guitar transformer to perform such a task and it simply will collapse.
It is all right to use a bass transformer for guitar. We do however loose a good part of the sonic characteristics that a good and well designed guitar output transformer offers.
On the other hand, using a guitar transformer for bass is a rather bad trade. In some cases you might even kill the guitar transformer and other vice damage the amplifier. At low volume and for practice a guitar transformer or a guitar amplifier can work OK for a bass.
For bass players using lots of top notes and overtones and/or particularly critic about the sonic quality a HiFi transformer may be the best choice.But as the bass instrument can not take advantage of the high frequency merits of the HiFi transformers it is hardly worth expense.
Output transformers are the most expensive part in a valve amplifier. Unfortunately this means that far too often manufacturing decisions concerning cost and weight are made to the detriment of quality. This is especially noticeable in bass amplifiers.
When the output transformers used are either too small or simply unsuitable, quality suffers and this is the main reason why many bass players are unhappy with valve amplifiers. Both the sound of the deep notes and the ability for dynamic performance suffers greatly from such poor solutions.
Whereas we can eliminate these shortfalls in the valve bass amplifier, we are still left with the problem of weight. Yes, granted. It is a problem that quality valve bass amplifiers are heavy. But if superior sound quality is your objective, nothing beats a proper valve amplifier.
BASS GUITAR AMPLIFIERS.
Good bass valve amplifiers do also need bigger power supplies; main transformers and electrolytics than a guitar valve amplifier of which all adds to cost and weight.
There is perfectly good reasons why a double bass is bigger than a cello.
These laws of acoustics also apply to electronics.
It is very difficult to cheat with natures laws of the physics.
For bass guitar, keyboard and PA amplifiers, please, see main transformers in the Audio HiFi transformer section.