2. amps-preamps
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Tube vs. Solid State for Dummies?

Hello everyone... I just discovered this terrific site, & have been perusing the multitudes of posts--very informative! Here's my question: Can someone explain--IN SIMPLE TERMS!!!--the difference in how a tube amp produces power vs. solid state, and why tubes have so much less current (while sounding warmer)? Here's my understanding (possibly inaccurate)of solid state...The capicitors are pouring energy to the output stage, and the flow of that energy is constricted by the output transistors. The transistors, responding to the input signal from the preamp, either constrict or release the flow of that energy/electricity to the speakers. I assume this is where the "power" is produced--that by clamping the flow, the pressure is increased (like putting your thumb over the hose). Is this true? On this point, how do tube amps do it? How does the tube (coil, collector,grid) upon seeing a very small amount of electricity, produce the "power" to move and dampen speaker drivers? Furthermore, can someone clarify the voltage/current relationship in all this? One of the definitions of high quality regarding amps is their current capacity, however this rule must not apply to tube amps, as they are low current, yes? Any feedback is appreciated, and thanks again for the great forum!
earhertz
sober1
18 posts
 
Get the book "The Complete Guide to High End Audio" by Robert Harley (2nd edition)
jcbtubes
400 posts
 
Dchace- Be careful not to get caught up into the "numbers game" associated with the current spec most often noted for ss amps. Though it may offer a relationship to the relative size of the power supply, and the number of output devices (and consequently output impedance and dampening factor), it offers no real indication to sound quality. As for power, remember that tube amplifiers use much higher voltage rails compared to ss. Power is voltage x current. The output transformer acts to impedance match the high output impedance tube stage to the low impedance speaker. The exception is the Output TransformerLess (OTL) tube amps that couple directly or through a capacitor bank to the speakers. Check into some audio amplifier design books for a much more detailed description for both ss and tube circuits. Goodluck.
sndsel
98 posts
 
You are developing your own theory and it's "not quite right." Best suggestion is to look into some books as recommended. Power is not "produced" in the output stages per se - the output devices "control" the power produced by the power supply from the AC power supplied by the elec co. While both voltage and current are certainly involved in both device types, tubes are voltage operated devices and transistors are current operated devices. That is a product of their physics. It takes higher voltage to create the electric field to support current flow through the almost vacuum of a tube. I won't get into solid state physics (partially because I have forgotten a lot).Both device types create a large output signal in response to a small input signal. In general, the ratio of output signal to input signal is called "gain". Yes, the output impedance of a tube cicuit is high, requiring impedance transformation to match a low impedance load like most speakers, while a SS amp circuit output impedance is low. The voltage (and current) is typically supplied to a tube amp circuit through the primary of an impedance matching transformer. Thus there is always a complete circuit through the tube even if the load is not connected to the secondary of the transformer. Power is then all dissipated in the tube. That is why you generally should not operate a tube amplifier without speakers. Oh! Oh! I think this is a book. Sorry.
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