[Ice Max]

I just got my first headphone amp a few weeks ago, and of course jumped right into tubes and got a LD MKIII

. As i was patiently waiting for my amp, i throughly read the Tube FAQ, so that i could familiarize myself with tube amps and know how to take care of them. So far ive been enjoying every bit of it. However, i noticed that there was no mention of tube arching. I had heard of it mentioned here and there befor,e but never knew what it meant. so what exactly is it?

 

[vcoheda]

if you don't have an LD2+, which arches and arching is bad, then don't worry about it.

 

[compuryan]

I'm not exactly sure what causes it, but its something internal with the amp. It is somewhat common on the LD2+. You'll see a little lightening bolt "arch" between two tubes. Quite frightening I think.

 

[Logistics]

Sounds like arcing, not arching.

 

[Negatron]

I was kinda' having fun with the speed of light thread but this is getting good.
(Some times tube-rolling can have it's breaks in routine.)

A guy in a lab coat with his hand on a double-knife switch looks up at the storm through the hole in the ceiling as lightnining bolts arch between a couple of Little Dot Amps, over and over. He throws the switch and yells! "It's Alive, It's Alive!

Seriously what happened in the LD II+ was a number of poorly constructed tubes from China. (it has happened) Tubes are constructed with very tight tolerences, Aero-Space tight. The cathodes on the LDII+ were directly heated so when the heater voltage hit the cathodes, they were cold and very low resistance so there was a pretty good current spike. At the same time the Plates were hit with full plate voltage 220v or so. (cathode-inductive/voltage leads current)

With current not yet flowing through the cathode resistor, the grid was not negative in voltage to the cathode, they were both at gnd. or earth. With sloppy tolerences the current would arc momemtarily between the plate and grid-cathode. Makes a pretty blue glow for an instant but since the cathode has now heated up the grid is negative and restricts the flow of electrons like it is paid to do and the music can go to work.

And no one has yet to explain what happens to bass as it is stretched at the event horizon of a black hole.

 

[spunkmeyer]

Yes, the term is arcing. Not an expert, but I believe it is when the voltage gets built up and jumps from the assigned path. It is not good, as it can cause carbon deposits and cause arcing at lower voltages subsequent times. Some of the causes can be as simple as dust or dirt, miswiring, poor insulation, current surges. I believe the thumping sound when an amp is turned on and off is due to arcing across the switch. A good quality tube amp should be properly fused and built to offer protection against arcing.

I don't own a tube amp. Perhaps someone who's got one can post any dos and don'ts about usage and maintenance.

 

[Negatron]

The arcing was inside the tube, not outside, It was a known problem and was do to poorly constructed old tubes. In time, it causes the tube to become 'gassy' or vacuum contaminated. With properly functioning tubes there was no problem with arc. Also since the output capacitor was connected directly to the heater/cathode, the turn on could be heard and some who had heard about arcing would assume their amp arced when actually it didn't.

The problem sometimes grew to mythical proportions. lightning bolts and such.

 

[vcoheda]

fyi, the problem with the ld2+ was not due to bad/old tubes, but faulty design.

 

[musicmind]

Quote:

Originally Posted by Negatron /img/forum/go_quote.gif And no one has yet to explain what happens to bass as it is stretched at the event horizon of a black hole.

Lol..where is "Team Blackhole Event Horizon" when you need them.
I suspect all that Hawking radiation is going to cause a lot of unwanted noise

 

[Negatron]

Quote:

Originally Posted by vcoheda /img/forum/go_quote.gif fyi, the problem with the ld2+ was not due to bad/old tubes, but faulty design.

I have several and with hand culled/selected tubes there is no problem with them. But It has allowed me to get them cheap.

 

[Negatron]

Quote:

Originally Posted by musicmind /img/forum/go_quote.gif Lol..where is "Team Blackhole Event Horizon" when you need them. I suspect all that Hawking radiation is going to cause a lot of unwanted noise

Need to get the team to direct a wormhole to suck all unwanted amplifier noise from this universe.

 

[jamato8]

With arcing you also get cathode stripping and there goes the tube. One reason I like tube rectifiers is the slow warm up and gradual ramping up of the voltage so current can get the resistors resisting and doing what they are supposed to do.

 

[Negatron]

Quote:

Originally Posted by jamato8 /img/forum/go_quote.gif With arcing you also get cathode stripping and there goes the tube. One reason I like tube rectifiers is the slow warm up and gradual ramping up of the voltage so current can get the resistors resisting and doing what they are supposed to do.

I completely agree. Almost every thing I build in recent years is tube rectified. Tube regulated for that mater. I've finally come full circle and don't use anything sand state in my builds. And electrolytics are evil! (That however presents a problem with my OTL H phone amps.)