Originally Posted by 7Sevin
I have no idea where to start with these. I know that they work via a vacuum, but that's all I know. What is tube rolling? Where can I find tubes? I'm planning on buying a Schiit Lyr at some point along with a Bifrost DAC and Audez'e LCD-2.
Sorry for this kind of post, I just couldn't find a general overview of how they work and the different kinds etc.
Thanks in advance,
How Tubes Work
Tubes work by applying a differential voltage between two metal plates. One metal plate (cathode) is set by the accompanying circuit at a much lower voltage than the other metal plate (anode). It is also heated by a separate heater circuit. The heater causes electrons to be emitted from the cathode metal plate. The other plate - at a much higher voltage (+ positive) means the electrons flow from the cathode metal plate to the anode metal plate. The flow of electrons causes and electrical connection and current flows between the two plates.
A grid, made of a type of metal mesh, is placed in the middle of the two plates. The grid is connected to the music signal that you wish to be amplified. The fact that the grid is in the middle of the two plates where electrical current is flowing, causes the signal to be superimposed on the receiving, or anode metal plate. That means the music signal, going through the grid, is "completely" replicated onto the metal anode plate, with the addition of whatever power/voltage was being produced by the cathode metal plate. That results in amplification of the music signal.
In the early days of tubes, many thought that a gas needed to be present to "convey" the electrons between the plates. As they got more experience with tubes, however, they found that the opposite was true - the current flowing between the plates was actually best when there was as near to a perfect vacuum as the equipment on hand could produce.
There's a little more to it than that, really - for instance, the cathode actually has a separate voltage applied to it in addition to being heated. What I described is known as a tetrode (3 points of electrical charge - cathode, grid, and anode). However, they added grids and other components to make many types of combinations - like a pentode: two plates and three grids (5 points of electrical charge).
Anyway, to summarize: the two plates sitting at different voltage values causes an electrical connection and current flows. Placing a grid between those two plates means the output plate's response is "imprinted" with the signal (music) applied to the grid, resulting in amplification.
Tubes were manufactured using mid-20th-century production techniques. In many cases, hand labor was significantly involved. Production processes also varied widely from manufacturer to manufacturer: the shape of the plates, the type of grid, the glass envelope, etc. The result is that most tubes of the same tube type might vary noticeably in sound signature. Further, so many tubes were made that many types are sometimes sufficiently similar to other types so that they can be substituted in the same [amplifier] circuit. The resulting difference in sound signature may be even more distinct than just manufacturer differences.
Over time, swapping out different brands of tubes - or further - different types of equivalent tubes, resulted in sonic changes that were somewhat unpredictable. Putting a positive spin on it - factors of different manufacture, different production dates, and different tube designs all meant that "improvements" in sonic performance might be possible. Thus, tube "rolling" was born - meaning the practice of swapping in and out different manufacture tubes or different equivalent tubes to see if the sound performance [of an amplifier] could be improved.
Google "vacuum tube dealers" or look on ebay. Just an FYI - ebay is uncharted territory. You are just as likely to find a $5 tube selling for $50 as you are a $10 tube selling for $5. One way to protect yourself on ebay is to reference the price for a particular tube type with the prices offered by the tube dealers that you found from Googling.