Black box?

[Paul O'Bryan]

How do you know when the BB tube needs
replacing? What sort of tube do they take
or is there a better one these days to replace the standard one?

[Gary Newcomb]

I’m curious on this too. I used mine recently on a long session and about halfway through, I took it out of the chain and it was like a fog or cloud had been removed and it was great improvement in the sound. I’ve had it for ten + years but by no means has it seen heavy use in that time. Perhaps that particular tube is just dying?

[Barry Coker]

You might want to do a search Brad Sarno has answered this question on a recent thread and there are tubes he recommends. I recently replaced the tube in mine and it made a difference in the tone.

Barry

[Peter Leavenworth]

When I was replacing the tube in my Black Box recently, I asked Brad Sarno if the Ruby Tube 12AX7AC5 I had on hand would work, he said that's what he would use. Users need to turn off the power to the BB at all times they're not in use to avoid needless wear on the tube - I have been surprised how often tubes in amps and effects have needed to be replaced if they're being used often.

[Brad Sarno]

Any vintage 12AX7 works great. For modern tube, we avoid ones with "spiral filaments". They can be problematic in the Black Box driver circuit. The modern Chinese 12AX7, 12AX7B, or 12AX7C are great modern clean tubes for this clean type of application. These chinese tubes from the Shuguang factory are also sold under the brands Groove Tubes, Ruby Tubes, and others.

Regarding powering on/off, I often leave my Black Box on for days on end. Little preamp tubes hardly use any power at all. Generally I'll fire up my rig in the morning, leave it on all day, then turn it off at night. Power tubes, on the other hand, should probably not be left on for such extended periods.

Tube can fail in the Black Box in a number of ways. The most common is a VERY gradual dulling of the tone, sometimes over a few years, so gradual you don't notice it. Other failures will sound like chaotic stormy noises or hum. Other failures are total silence.


Brad

[Gary Newcomb]

Brad, thanks for this info AND thanks making all this cool shit!!!

[Kevin Mincke]

I might add depending on how old your BB is, it may require the old 12ax7u like mine.

[Brad Sarno]

I might add depending on how old your BB is, it may require the old 12ax7u like mine.

Thanks Kevin. True, the earlier non-updated BB's ran on a 12AU7 and without correct mods, they don't run that well with a 12AX7.

B

[Steven Paris]

..... the earlier non-updated BB's ran on a 12AU7 and without correct mods, they don't run that well with a 12AX7.

Mod to run AU7 instead of AX7? Hmmmm....never heard that....WHAT mod?

[Derrick Unger]

Love the black box for taking out the shrill highs you get with some amps..

[Dave Mudgett]

..... the earlier non-updated BB's ran on a 12AU7 and without correct mods, they don't run that well with a 12AX7.

Mod to run AU7 instead of AX7? Hmmmm....never heard that....WHAT mod?

It's not a mod to run 12AU7. The early versions, like mine, were originally designed around the 12AU7 tube. Brad's saying they don't work so well with a 12AX7 without a mod to take the AX7.

[Gary Newcomb]

My BB is SN: 0488X
12ax7 ?

[Stuart Tindall]

Mine is 0438 12AU7