[amblin]

Hi all
 
 Finally, I crossed the bridge and gotten into the world of tube amplification.. (barely)    maybe someone'll say that it's not for noobs and they require alot of patience.  Yeah, i agree, and i admit i didn't think that far ... 

 Back on topic, when i cold start my amp, i see a rather bright flash from the base of the tube (one out of four AX7s), for around a second in duration and of the same colour when they're hot.

I already done a quick search and it seems that it's because the heater winding is very low resistance when cold, but how come the other three are perfectly 'normal'?  Does it mean this particular one is going to fail?  Or worse, it's the 'normal' three being un-normal...

And btw, i got slight oxidation on most of the power tube contacts , is there a simple and efficient way to clean them?

thanks and best regards

A

EDIT: if it's indeed caused by low resistance in the cold heater winding,  then there must be a surge, which could eventually toast the tube exactly like most light bulbs burn out at the time they're switched on, right? So what if i use the hair dryer to 'warm' them up abit before switching on?  my wife got a really powerful one..

[Ericus Rex]

Tube flash is perfectly normal with some types of tubes.  It doesn't necessarily mean they will wear prematurely.

[amblin]

Tube flash is perfectly normal with some types of tubes.  It doesn't necessarily mean they will wear prematurely.

Ah, thanks and that's good news. 

[wilsynet]

Check out your local Radio Shack.  Get some Deoxit contact cleaner (not protectant, but cleaner) and you can remove the oxidation with the spray and some Q-tips.

It's a good idea to clean tube pins and cable terminations once in awhile.

[InfernoSTi]

I have found that my Mullard CV 4024 has a huge flash that was very normal.  I thought only the British tubes did this, though....

John

[Ericus Rex]

I had a pair of Quicksilver Silver 60 monos and the 12DW7 supplied flashed at startup just as you describe.  I emailed Mike Sanders of Quicksilver and he said the flash was perfectly normal and not to worry about it.  I later replaced the tubes prior to selling the amps and I remember the replacement tubes (JJ, I think) did not flash at all.  I can't remember what was in that spot originally though, but given when the amps were manufactured they very well could have been Yugo.

[bunnyma357]

My East German RFT ECC82 (12AU7) tubes flash, the RFT ECC81 (12AT7) tubes don't.

Jim C

[pehare]

from the owners manual of my Music Reference amp...."You may notice a bright flash from the bases of V1 & V2 (both Ei 12AX7's) on turn-on.  This is perfectly normal & does not shorten the life of the tube in any way.  The flash is due to the fact that the filaments are coated to insulate them from the tube cathode sleeve.  In the process of connecting the tungsten wires to their pins, the coating has been removed.  This uncoated portion has less thermal mass & thus heats quickly, causing the flash."

My personal amp's tubes don't flash but a friend's identical amp has one 12AX7 that flashes on startup.  No sweat....

[amblin]

from the owners manual of my Music Reference amp...."You may notice a bright flash from the bases of V1 & V2 (both Ei 12AX7's) on turn-on.  This is perfectly normal & does not shorten the life of the tube in any way.  The flash is due to the fact that the filaments are coated to insulate them from the tube cathode sleeve.  In the process of connecting the tungsten wires to their pins, the coating has been removed.  This uncoated portion has less thermal mass & thus heats quickly, causing the flash."

Aww i wish my amp had such a helpful manual... i bet it even explained how to re-bias the tubes in fine detail along with some nice pictures......

i on the other hand had to spend some hard earned bucks on a man to re-bias the thing for me... Because the ports're all hidden under the chasis and my owers manual mentioned nothing about how , where to adjust and what value to shoot for...


  Thanks for all the replies

[ltr317]

I have found that my Mullard CV 4024 has a huge flash that was very normal.  I thought only the British tubes did this, though....

John

Mullard was a subsidiary of Philips, and its other subsidiaries like Amperex use similar tooling, so those family of tubes all flashed when they were new. 

[Faust3D]

This is perfectly normal and has to do with internal constraction of some ECC83 aka 12AX7 tubes. When the filament is first energized, it flashes very bright for a second and then dulls down to the normal soft orange glow. Other tubes do this as well such as Amperex Holland, Mullard, Matsushita and Ei Yugosolvia.  These tubes should do it all the time trough their life span.