Tube flare on power-up?

[moosapotamus]

Howdy,
I think I might be in need of some educated advice...

My first HV tube curcuit built up from scratch... an Alembic F-2B. Sounds great, awesome with my Vox hollow-body bass.

But, when I power it up, I get a quick (~1 second) little white flash inside the 12AX7, down at the base near the pins. I've never noticed anything like this with any of my other tube gear, so I'm assuming it's not good.

Can anyone tell me if this might really be a problem? Am I doing something dangerous? Am I gonna fry somethin'?

Power supply is ~314VDC plate, 6.3VDC filament. The rest of my build info is here...
http://moosapotamus.net/IDEAS/F2B/alembic.htm

Thanks!
~ Charlie

 

[12afael]

http://www.groupdiy.com/index.php?topic=9027&highlight=light+tube

is already treated.

 

[rodabod]

You get flashing or flaring with some brands /models of valves.

Have you tried an alternative model?

 

[moosapotamus]

Thank you, gent's!
Yes, seems to be just this Ruby 12AX7 (Yugoslavia).
None of the other tubes I have on-hand seem to flare on power-up.

Thanks!
~ Charlie

 

[Gus]

Charlie

I like to add a resistor between the diode bridge and the first cap of the fil supply. Adjust it so you have >2 volts more than the fil reg voltage you want at the input to the three term reg.

less switching noise from the diodes, limits the turn on current surge, limit the heat in the reg.

FWIW getting ready to build a funny cat.

 

[dabo]

Our Chilean friend got it right in the earlier posts. The heater resistance is lowest upon cold start and increases as soon as it heats up.
I've never had a tube fail due to this effect.

 

[moosapotamus]

Thanks, dabo!

Gus, that's a great tip. Thanks!
That LM317 does get awfully hot. Heat sink is definately a must.
Also, as an aside, I tried 12V, 6.3V and 5.6V on the heaters and didn't think the difference was huge. But, 12V did sound kinda thin compared to 6.3V and 5.6V. I'll probably just keep it at 6.3V.

The funny cat is a blast. Don't know if you noticed, but I've got all my info on that one back up on my site, including some pics of an original on my IDEAS page. Definately try replacing the feedback resistors on the opamps with 1M pots. Wild stuff. :wink:

Thanks, again!
~ Charlie

 

[Andre]

I've built one of these for my bass player. They're quite nice. It has turret board construction with A/C heaters that produce just a little too much hum. I've been thinking about doing another one with 1 channel F-2B and the other Amp*g- and regulated DC heaters. Then maybe to complete the setup I'd built a Hiw*tt style output as a seperate unit.

Anyway, may I recommend using JJ brand tubes for your tube gear. I say this from my own limited experience as well as countless listening tests performed by others who write into the AX84 board.