PreSonus TubePre - broken out of the box?

[soniceye]

Can anyone tell me if the buttons and meter are supposed to light up when it's functioning? No lights work except the clip LED, comes on when I tweak the drive and gain knobs, but no signal, just a hum. Two tiny LEDs on the circuit board light up directly under the tube, misleading me to think the tube was working, until I opened it up.

[newkid]

what does the fine manual say it should do ?

[soniceye]

solved, wrong power supply. For now on that's gonna be the first thing I check!!!!!!

And yes, buttons and meter light up when functioning.

[Electriclight]

Originally Posted by soniceye

Can anyone tell me if the buttons and meter are supposed to light up when it's functioning? No lights work except the clip LED, comes on when I tweak the drive and gain knobs, but no signal, just a hum. Two tiny LEDs on the circuit board light up directly under the tube, misleading me to think the tube was working, until I opened it up.

Many one tube preamps use LEDs under the tube to simulate something really neat going on. Don't expect the tube to actually glow, ever. Can't help with other questions, sorry.

[newkid]

Originally Posted by Electriclight

Many one tube preamps use LEDs under the tube to simulate something really neat going on. Don't expect the tube to actually glow, ever. Can't help with other questions, sorry.

Did tubes change?
Are these just transistors with a glass cover now ??

The filaments always glowed red. Only way to generate free electrons for the plate to attract.

Plate usually only glowed when dissipating too much power.
But some high power output tubes glowed normally.

[Electriclight]

Originally Posted by newkid

Did tubes change?
Are these just transistors with a glass cover now ??

The filaments always glowed red. Only way to generate free electrons for the plate to attract.

Plate usually only glowed when dissipating too much power.
But some high power output tubes glowed normally.

The < $100 preamps are not pushing a 12AX7 tube hard enough to visibly glow.

(Umm, red light wavelengths are not an indication of free electron flow - just heat, you do realize this I guess?)

Maybe you have a better explanation for the LEDs beneath the tube???

[newkid]

Originally Posted by Electriclight

The < $100 preamps are not pushing a 12AX7 tube hard enough to visibly glow.

(Umm, red light wavelengths are not an indication of free electron flow - just heat, you do realize this I guess?)

Maybe you have a better explanation for the LEDs beneath the tube???

Agree they should not be pushed to make the plate glow.
But filaments always glow.

Heat is energy. Energy loosens up the electrons on the surface of the filament so the plate can pull them with its plus voltage.


LEDs are neato looking so I think marketing gimmick.

[Electriclight]

Mullard 12AX7 no glow - AudioKarma.org Home Audio Stereo Discussion Forums

LEDs are neato looking so I think marketing gimmick

Many one tube preamps use LEDs under the tube to simulate something really neat going on.

Why didn't I think of that?

[brandondrury]

We are probably discussing the extent to which a tube filament glows. Obviously, in a cranked guitar amp they grow a bright yellow. I've seen them barely glow at all in various circuits. I wouldn't be surprised if the glow as ALMOST no existent, but I can't help but question the effectiveness of a tube that isn't being pushed.

Of course, that brings up a bigger issue. What is the function of 2 tubes in an 8 channel preamp? My first guess would be the power supply section. They'd need at least 8 tubes for Class A operation and at least 16 tubes for Class AB. Regardless, it's clear the tubes aren't part of the actual audio amplification unless I'm just forgetting a big chunk of electronics from 10 years ago.

Brandon

[newkid]

Originally Posted by brandondrury

We are probably discussing the extent to which a tube filament glows. Obviously, in a cranked guitar amp they grow a bright yellow. I've seen them barely glow at all in various circuits. I wouldn't be surprised if the glow as ALMOST no existent, but I can't help but question the effectiveness of a tube that isn't being pushed.

Of course, that brings up a bigger issue. What is the function of 2 tubes in an 8 channel preamp? My first guess would be the power supply section. They'd need at least 8 tubes for Class A operation and at least 16 tubes for Class AB. Regardless, it's clear the tubes aren't part of the actual audio amplification unless I'm just forgetting a big chunk of electronics from 10 years ago.

Brandon

Well.....
In my elex classes they ran a single tube in class A.
Or in class C. But two tubes were used for class B.
Don't recall AB but sounds liek that would take 2 tubes too.

Never saw a workign tube where the filaments were not at least orange. They glow from the "C" battery (or equivalent power).
Have nothing to do with the plate voltage or power dissipated or output. Only function is to make electrons available at the cathode. The high voltage on the plate attracts them, the grid bias regulates how many and allows their flow to be modulated.

Saw some RF output tubes with the plate glowing red, but never an audio tube.

Have heard of the grid glowing in a radio amateur transmitter that was being way overdriven. Cannot confirm that.

The power supply was usually solid state diodes. Tube diodes went away by the time of superhet AM radios.

We need the circuit diagram to know for sure what they are doing.