Do you leave CD players with tube outputs on?

An excellent writeup by Raquel, and excellent advice.

For the record, though, I'd like to cite a couple of minor points that I believe are mis-stated.

Most small signal tubes that are used in audio components, such as the 12AX7's and 6SN7's, use indirectly heated cathodes (meaning that filament and cathode are different elements). The filaments in some designs are powered with low voltage ac supplied directly from a winding on the power transformer, in which case tube vs. solid state rectification has no bearing on the in-rush current to the filaments that occurs at turn-on. Better designs often incorporate dc filament supplies, in which case the design may provide better in-rush control.

In either case, controlled ramp-up of the rectified high voltage that is applied to the plate circuits (that can be provided for in the design of a good solid state rectifier circuit, or that occurs naturally with tube rectification) prevents plate voltage from being applied before some degree of warmup of the filament (and consequently the cathode) has occurred. Application of high voltage to the plate (or screen, or other high voltage elements, if present), prior to establishment of what is called a protective "space charge" of electrons around the cathode, leads to a phenomenon called "cathode stripping," which in the case of some tubes can shorten tube life considerably (although its significance in the case of small signal tubes is controversial).

Cathode stripping occurs, I believe, as a result of stray gas molecules in the tube being positively ionized by collisions with electrons being drawn toward the positively charged plate, the collisions causing electrons in those molecules to be knocked away. The positively charged, heavy, ions are attracted by the cathode due to its low potential, where their impact would damage the cathode's emissive surface over time were it not protected by the space charge.

Again, thanks to Raquel for the excellent writeup.

Regards,
-- Al

Hi Abe,

Thank you for the polite nature of your questions, but I'm not able to answer them particularly knowledgeably.

Yes, I would think that a suitable high-current thermistor, suitably placed somewhere in the path between ac inputs and tube filaments, would be an effective means of inrush current limiting. I know that is commonly done in power supply designs, although I don't have a feel for how widespread their use is in audio.

I'm not sure I understand your reference to shorting of caps, but that would seem to only be relevant to designs that incorporate a dc filament supply, not to those that drive the filaments with low voltage ac directly from the transformer.

Re cathode stripping, as I indicated its significance with respect to small signal tubes is a matter of some controversy, and I have no particular feel for its degree of significance myself. But given the possibility of it being significant, it would seem to be good practice to design a tube component to bring up the B+ slowly.

Regards,
-- Al

I have left my player on for 72+ hours and do hear improvements in sound stage both width and depth, and a little more detail. The CD player runs quite warm to the touch -- Is heat a concern??

Hchilcoat -- It's hard to say. I'm not sure which Ayon player you have, but if it is the CD3, with 4 x 6H30 and 1 x 6AX5 tubes, and if it does not have a low-power standby mode, its power consumption is well above average for a CDP, and would easily account for the heat you noted. That would be a bit less true of the CD1 and CD2.

I don't have complete specs on those tubes, but it looks like the filaments alone draw around 5 watts for each of the 6H30's, and around 8 watts for the 6AX5. Factoring in plate dissipations, and power for other circuitry, I suspect that the 50W consumption specified in their datasheet is a bit understated.

Whether or not that would pose a reliability problem in the long-term would be dependent on how well the thermal aspects of the design handle the heat. The 25kg (about 55 pound) total weight of the two chassis, and the fact that the unit is split into two chassis, is suggestive of good design in that respect.

But beyond that I would say that your guess is as good as anyone's, unless the manufacturer can offer specific credible advice.

Regards,
-- Al