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-- My pre-amp tubes were faking it.

My pre-amp tubes were faking it.

Hey kids, thought you might get a kick out of this. I re-tubed my preamp over the weekend and made an interesting discovery.

I've peeked through the air vents at the 12AU7 tubes inside glowing orange... I assumed because tubes in my mind were supposed to get red hot.

See FIG1


So I removed the old tubes to replace with the new ones... (yes I unplugged it first) and what did I discover? But an orange LED light down in the tube mount. yeah, the tubes get warm... but not red hot, and my preamp was faking it for the look~! What a disappointment!

FIG2

thats interesting. how does it sound?

haha you got vtec'd

quote:

Originally posted by camsr thats interesting. how does it sound?

Well, long story short, way better than before. I got some JJ/Tesla replacements and they rock. the gain ratio is tad hotter than the old ones, but I'll survive.

i think i mentioned in another thread that anytime you buy any gear with tube pre's, they usually load em with crap-o chinese production tubes. Not totally the case here, but pretty typical. worth the $40-50 upgrade.

quote:

Originally posted by Leon haha you got vtec'd

totally. this is a DBX 386 dual channel pre. I called a friend with a diff DBX unit and his had the same thing. Based on some research today, I have to assume any gear with tube pre-amps is using the fake-o technique above.

quote:

Originally posted by Leon haha you got vtec'd

vtec pwns joo!

Okay enough of that.



Reddick, Man I HATE things like that. At the NAMM show I saw a keyboard with some tubes in it. The sad part was that they had 3 TINY LEDs on wired POINTING at the sides of the tubes randomly. I'm going to try to meet with THD this week and throw out the idea of a HOT tube preamp setup. They do well with their hot-plate setup to crank tubes up and then attenuate the output.

quote:

Originally posted by 3F05Q I'm going to try to meet with THD this week and throw out the idea of a HOT tube preamp setup. They do well with their hot-plate setup to crank tubes up and then attenuate the output.

Do it. I'd be into that shit.

quote:

Originally posted by CReddick Do it. I'd be into that shit.

Really? I'd like to get a rollcall on such a thing.. maybe? I'd be lying if I said I wasn't trying to get a job!

Haha, theres a Behringer tube thing that does the same, looks like it glows and its because its got an LED behind it.

Here, I found a pic:

quote:

Originally posted by Sanguis Mortuum Haha, theres a Behringer tube thing that does the same, looks like it glows and its because its got an LED behind it.

Wow... I feel like we've uncovered some sort of conspiracy or something.

consumers get a kick out of it, so the manufacturers fulfill their desires. Doesn't make any difference to the sound, so I don't care.

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?

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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