Crack Tubes and when to replace

[DirectAssault]

Morning,

As the title suggest, at which point should I be replacing the tubes on the crack. What are some tall tell signs that the tubes are on their last legs?

[Paul Birkeland]

If the voltages on terminals 1 and 5 get really high, like say over 110V, that indicates a dead tube.

The 6080's voltages will move around a fair amount depending on what the 12AU7 is up to, so that's a bit harder to determine.  If you keep a spare around you can pop it in every 2-3 years to see if the sound improves dramatically, which is a reasonable way to test a tube in the absence of a tube tester.

[DirectAssault]

So I have the original Tubes that were with my amp when I purchased it back 6 years ago. It's essentially my daily driver with around 4-8 hours of usage everyday.

The voltages on those terminals were fine when I checked it out, but I know the tubes aren't dead yet. Just trying to troubleshoot my issue from a few months ago from thread https://forum.bottlehead.com/index.php?topic=12744 which I never got a resolution on.

At any volume level, I'm getting what my friend described as an "8-bit heliocopter noise" coming from my headphones. Just trying to determine if getting a new set of good tubes would solve the issue.

[Deke609]

Can you move the Crack to another room and plug it into a different power line to your breaker panel and try it there? What you describe could be RFI interference -- e.g., from a nearby phone, computer or wifi router, and not necessarily yours (if you happen to live in apartment).

Did you install the diode mod discussed in your previous thread?

cheers, Derek

[DirectAssault]

@Derek,

I've not tried the diode mod, though after some testing, I think you're right that its related to RFI. With that being said -- maybe you could help explain something

So I tried it across 4 rooms in my house.

my office, an empty bedroom, a kitchen, and the living room.

The only one that I was able to reproduce the "helicopter" noise was from my office. Cool! but here's the weird thing. It's not consistent in my office. After unplugging it, letting the capacitors drain, and trying it in my office. I wasn't able to get the helicopter noise. But if I were to plug it from one socket to another in my office, sometimes the sound would come back.

So I can't rule out that the same thing isn't happening on the other rooms, but right now, there's no noise on the same circuit I was just on 10 minutes ago.

I would think that if its RFI, it would be constant along the same circuit. I even put the circuit under a heavier load (just running more things at once) and the sound isn't returning.

[Deke609]

maybe you could help explain something

I'm more likely to add to any confusion than to clear it up. I'm just a noob.   

But one thing I should and can clarify is that I didn't mean that trying different rooms and house-wiring lines would only test for RFI; just that it was one possible explanation worth exploring. Another possibility is noise on your ground wiring.  You may want to investigate what else you have plugged into your wall outlets around the house. I think the folks at BH and on this forum can probably list some of the usual known culprits.  I recall that dimmer switches can be a source of noise. I believe the diode mod would address and potentially eliminate a problem of ground noise.

cheers, Derek

[Paul Birkeland]

8 bit helicopter noise is how I would describe interference from a cell phone trying to talk to a cell tower.  If you put your phone in airplane mode, what happens?

[DirectAssault]

I threw my cellphone against the thing and made a call, it's not the same kind of interference noise that I am experiencing.

Have you ever played the "Helipcopter Game"?



The sound the helicopter makes while going up is the type of sound I am experiencing. It's a type of low pitched oscillation

[Paul Birkeland]

Definitely wireless interference. 

[DirectAssault]

Would the diode mod even help in this situation then?

[Paul Birkeland]

You could give it a shot, it won't hurt anything, but I don't suspect this will help.

You can put a 0.1-1uF Z5U cap between terminal 22L and the ground tab of the red RCA jack.  That can send some wireless nasties to earth rather than into the circuit, but your mileage may vary on that one. 

I don't suppose you have an ethernet over powerline kit?

[DirectAssault]

Nope, things are either on WiFi or directly plugged into the router. And because of how the house's wiring is, the router has to stay in the office, though I could move it 3 feet further away from it. Though I suspect that it wouldn't change much.

I'll do the diode thing, like you said it wont hurt it.

I imagine trying to Z5U also wouldn't hurt. Can you give a bit more specification on the Z5U capacitor? is it better to go for 1, or 0.1, or in between? Voltage rating? Part number? Haha

[2wo]

Cell phones make that kind of noise when you are not actually using them, looking for towers, reporting your every move to central control, that sort of thing. You can try unplugging your router, it's process of elimination at this point.

On the other hand your tubes have some miles on them, wouldn't hurt to pick up a new set...John

[Doc B.]

Try cleaning the tube pins. Could be an intermittent connection in the socket from oxidation if the tubes have been in there for 6 years.

[Paul Birkeland]

I imagine trying to Z5U also wouldn't hurt. Can you give a bit more specification on the Z5U capacitor? is it better to go for 1, or 0.1, or in between? Voltage rating? Part number? Haha

Buy what's convenient to get if you can get something locally or conveniently.  The voltage rating doesn't matter.  I'd probably opt for 0.1uF.