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Solid-State TUBES !!
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peter-h:
I used to design with valves. EF80, ECC83, EL84, KT66, KT88, even the big 807 for pirate radio transmitters :)

A valve is basically a depletion mode N channel mosfet. Like the mosfets we have today but if Vgs=0 it is fully conducting, so the gate needs to go negative to get into the controllable region.

Hence valve circuits, to avoid a negative rail, have a resistor in series with the cathode, which lifts the cathode up by some 10-20V, so if the grid is near ground you have in effect a negative Vgs.

The only advantage of valves is that they were electrically very robust, and short of mechanical destruction they would be very hard to damage. This was good for rudimentary EMP protection :)

Valve amps are crap. It is purely a fashion thing. Many years ago, QUAD did a blind test of their 1950s valve amp and the then state of the art 405 amp. The audience was a load of hifi press VIPs. Nobody could tell the difference, statistically, between the two amps. The THD was a few % versus 0.01% or so...
T3sl4co1l:

--- Quote from: peter-h on April 14, 2020, 03:43:00 pm ---The audience was a load of hifi press VIPs. Nobody could tell the difference, statistically, between the two amps. The THD was a few % versus 0.01% or so...

--- End quote ---

And double-blind tests have been banned in hi-fi circles ever since.* :-DD  That tells you, basically all you need to know.

*I mean, I don't know that this story is true and the origin of that aversion, but it's the general idea in any case.

Tim
engrguy42:
Anyone notice how discussions of analog stuff like scopes and tubes invariably end up with justifications like "it's like a fine wine" or "it's like driving a Bentley or a Mercedes" or  dissing those who buy "cheap plastic toys from China"?

Please, tell me there's more to it than that  :-DD

Look, if you like it just cuz you like it then admit it. No need to search for irrelevant and meaningless justifications to make it look more honorable.   :-DD

Reminds me of the PC techies who pee in their pants when a "faster" GPU with more fans and shiny lights comes out. Even if it's only 10% faster, with software that hasn't been developed yet. "Ooooo, more POWER !!!"   
Tomorokoshi:
I don't need solid-state tube replacements. I tracked down the problem 2D21 just fine. What I really need is a schematic for the thing. Otherwise obscuriorata is difficult to fix.
frozenfrogz:

--- Quote from: peter-h on April 14, 2020, 03:43:00 pm ---Valve amps are crap. It is purely a fashion thing.

--- End quote ---

I do not fully agree.

For hifi stuff, I do not see much benefit in tube technology either and there is a sh*tload of voodoo devices with tubes in it, that do not actually give any benefits aside from looks and marketing blerb. However, I really like playing tube amplifiers on electric bass and electric guitar.
Yes, there are some digital modeling amps that can pretty much reproduce what the original tube amplifier sounds and feels like. However, these are expensive AF and just do not "click" with me. It is a bit like using the screwdriver on a multi-tool. It gets the job done, but a dedicated screwdriver with a nice wooden handle makes the job more fun.
There is nothing more satisfying than playing through my Mesa Bass 400+ or Peavey 3120.
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