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| quote: | Originally posted by richg101
hahaha. so modern tube gear doesnt glow? i remember my dads tube guitar amp's tubes glowing. but this was over 20 years ago. i always thought they glowed during use. why would they need to fake it with the led's? |
A tube glows when it's running 'hot'. Meaning you turn the cathode voltage up quite a bit. In a lot of modern audio equipment this is either undesireable, unnecessary or expensive to implement. I dunno, but I'm leaning toward undesireable for things like a tube-pre? A lot of the cost, actually, is sunk into the output transformer, which greatly affects the sound output. I've actually seen output transformers in the 4-digit price range.
So anyway, they use LEDs to make it look cool because it's not glowing as much as it would in a situation where it'd be running hot.
Tubes are pretty genious, really. If someone doesn't know how they work... here ya go, with the simple version: You've got a cathode that emits electrons due to a very high voltage source, a plate (anode) that electrons flow to, and a control grid between the cathode and anode that controls the flow of electrons. The input signal goes to the control grid and the output is the plate. So you can see how that amplifies the signal. There are a lot of other bits in there, but that's just to clear up other issues such as capacitance, since the cathode and anode are essentially parallel plates.
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