Tube troubles - 6080 [solved]

[Loquah]

Hi all,

The central ceramic tip on the base of my 6080 (as supplied with my Crack) broke off the first time I used it. Eileen was kind enough to send me a replacement which looks mint, but rattles as if something metallic is loose inside. I'm assuming that's a problem. I've turned the tube around in my hands and can't see a loose piece or anything moving significantly, but it sounds like a small piece of metal is loose within the tube.

I'll plug it in and test it tomorrow, but I'm worried that I've got another damaged tube. The trip to Australia must be rough!

Is this just a simple case of testing the rattling 6080 or is a metallic rattle an instant write-off in a tube? I.e. if it sounds OK could it be OK?

Also, is the missing central tip (the part that goes down into the centre of the socket) an issue if it sounds fine? Maybe I can stick with my original one if the central tip isn't crucial.

[Loquah]

I've managed to see what's making the noise in tube 2 (the rattling one). It looks like small pieces of glass. I can't see any broken parts so figure the glass tip of the tube (inside the plastic base centre pin) must be broken. Is that an issue? Are these tubes supposed to be a vacuum? I imagine the plastic base plate isn't air tight if the glass is broken.

[Laudanum]

The central "tip" is actually a small guide or "key".  Basically, a "keyed" tube/socket.  The only thing it really serves to do is to make sure the tube is oriented properly when insterting in the socket.  As long as it is, the key doesnt affect the tubes actual function.  In other words, the tube is fine to use.  Just always make sure it is correctly inserted into the socket which shouldnt be a problem if you remain mindful of it and if there is some remnant of the "key" so you can reference proper orientation.

Usually (or atleast most often) the rattle is caused by a small piece of mica (from one of the spacers) or spacer material that has chipped off and now rattles around in the tube.  If so, it is benign and doesnt affect function at all.   I have 3 or 4 tubes of different types that rattle because of this.  Mine are all fine.  It could be a potential problem if it's a piece of metal that can cause a short so I dont think it's safe to make a 100% guarantee that it's fine to plug in.  Try to ID the piece.  Look for a missing chip from one of the spacers as that's most likely what it is.  Although, sometimes you wont see where it came from but will still be able to ID it as a piece of spacer material or maybe even a piece of glass.  It's most likely fine, but again, I dont think one could make a 100% for certian guarantee in the off chance that it is a small piece of metal.   A tube tester would quench any doubt but doesnt help if you dont have one.  Plugging it in will quench any doubt as well  

[Laudanum]

Posted while you did.   You could have a chip or bead of glass loose in the tube without it losing vacuum.  It isnt necessarily an indicator that the vacuum seal isnt intact.  If you plug it in and getter goes white/gray, (normally silver/silverish) you'll know.  I think you would see it quick but dont think it can hurt the amp. 

[Doc B.]

Actually the getter would flash white within a few seconds if the tube had a leak whether you plugged it in or not. I've had lots of tubes with a tiny piece of loose glass and use them without any problems. It's probably fine. The tube with the broken pin will work as long as you are fastidious to install it with the pins in the correct holes. I usually mark the base of the tube with a line where the ridge on the old center pin was. You can buy an octal center pin "prosthetic" from www.tubesandmore.com to replace the broken one.

[Paul Birkeland]

The rattling material is very normal, especially on octal-sized tubes. I would say about 20-30% of the tubes I own of this size will exhibit this rattle.  It can sometimes be a small piece of glass or mica rattling around, which is not a problem. 

[Loquah]

Thanks for all your answers and information everyone. Very helpful!

[Loquah]

Ok, so I've tested the rattling 6080 and it creates the strangest sort of microphonics. When the 6080 is warmed up (I left it on for about 10-15 minutes before using, but after also watching for a few minutes to insure it din't burst into flames!) it creates a strange harmonic ringing sound if I bump the chassis. There is also some static in the circuit. I haven't yet isolated if this is coming from the replacement 12AU7 that Eileen also kindly provided.

1. Should I burn the new 6080 in for a while to see if it rectifies or is it toast if it's creating these weird harmonic microphonics?
2. I'm guessing that the static could just be the result of the pins needing a clean. Is that true?

[Paul Birkeland]

Microphonics are also normal and not a cause for discarding a tube (unless it is set off by something like a sneeze).

For the static, you can remove the 6080 and scrub on the pins a bit with some steel wool.  Same for the 12AU7, just be gentle with those tiny pins.

If the static and microphonics only happen when you tap the tubes, then the solution is to not tap the tubes

[Loquah]

Fair point, CB - thanks! 

I'll try cleaning the pins and re-test, but have also just ordered a bunch of new (upgrade) tubes from a local supplier based on the various recommendations I've read on here. Hopefully I'll have a better than ever Crack before the end of the week.

[Laudanum]

Just a quick point.  And I didnt realize this until building Crack as it was my first tube headphone amp.   A tube that only proves to be microphonic when tapping on the tube or amp chassis etc;  obviously isnt  necessarily a problem in a heaphone amp or in the signal chain with a heaphone amp.  That is, unless you are dancing on a wooden floor, or maybe even toe tapping while listening through your cans   
But that same tube in the signal chain of an amplifier for a speaker system very well would be, or atleast could be.  If, the soundwave from the speakers agitate the tube enough to cause it to transfer the microphonics through the system so that they are amplified and reproduced by the speakers.   Nothing earth shattering here, just never thought about it before Bottlehead Crack.  But the point is that should you have any tubes that are too microphonic to use in the speaker system,  they may very well be usable with the headphone system, assuming compatible tube types of course.  I have a couple 12AU7's that would fit the bill here.

[dlefco]

Hi all,

The central ceramic tip on the base of my 6080 (as supplied with my Crack) broke off the first time I used it. Eileen was kind enough to send me a replacement which looks mint, but rattles as if something metallic is loose inside. I'm assuming that's a problem. I've turned the tube around in my hands and can't see a loose piece or anything moving significantly, but it sounds like a small piece of metal is loose within the tube.

I'll plug it in and test it tomorrow, but I'm worried that I've got another damaged tube. The trip to Australia must be rough!

Is this just a simple case of testing the rattling 6080 or is a metallic rattle an instant write-off in a tube? I.e. if it sounds OK could it be OK?

Also, is the missing central tip (the part that goes down into the centre of the socket) an issue if it sounds fine? Maybe I can stick with my original one if the central tip isn't crucial.

I'm a brand new Crack user, purchased an already assembled build from someone just prior to the holiday. Forgetting they are keyed, I naively jammed my large tube into the socket. Now the amp is not producing sound, the 6080 is not heating up, and the tube rattles like a blown light bulb. Will try another 6080 tomorrow but worried I've damaged the pins or worse. Any quick thoughts?

[Doc B.]

Need more info. Did you break off the keyed center pin? Did you try putting the tube in the correct way before you determined that it is not working? Does the Crack have the Speedball upgrade? Do you have a copy of the manual in case you need to troubleshoot it?

[dlefco]

Need more info. Did you break off the keyed center pin? Did you try putting the tube in the correct way before you determined that it is not working? Does the Crack have the Speedball upgrade? Do you have a copy of the manual in case you need to troubleshoot it?

Thanks so much for the quick reply!
No, all is intact; nothing seems to have broken. Yes, tube is inserted correctly and no longer heats up, and no sound produced from the amp. Does include Speedball. The seller did send me the user manual and here is what I see as reccommended troubleshooting:


No sound - something isn't getting voltage or it isn't getting signal. Before you dive in to tear things apart, check the obvious - are your speaker cables hooked up properly? Interconnects? Is every- thing switched on? We see some slightly embarrassing moments at Bottlehead meetings, where the equipment is often swapped in and out of the system at a frantic pace. About 95% of the time a "dead" piece of gear just isn't hooked up right.[/i]

[dlefco]

Unplugged all cords, removed and reinserted both tubes and all is back to normal! False alarm. Thanks again for your attention