temporary intense glow/dull flash on filament when heaters are turned on

[unparalleled]

200 XL - 6550s, it was ready for the dump when I got it!
Replaced everything except the preamp pcb and the transformers.
Made a new power amp PCB, original board was charred.
restored the cabinet also.
I used 3x 33uF 450v electrolytics to replace the ones on the PCBs, I have plenty of these NOS caps if you want some. (they are small axial lead type and fit perfectly)
Some of the diagrams on anz site are missing cap values I can fill in the gaps there.
Roly the web site owner wants me to send him pics which I will send him when I have written some blurb to go with them.

There is now a feature on ANZ amps about my rebuild, although it describes making a new PCB he has put up a Photo of the wrong board. I have advised him and he will no doubt change the photo in due course.

[black_labb]

There is now a feature on ANZ amps about my rebuild, although it describes making a new PCB he has put up a Photo of the wrong board. I have advised him and he will no doubt change the photo in due course.

just had a look, very well done.

[Steve Conner]

I don't buy the "burning air" thing either.

(To be pedantic, your V8 burns air already, or rather burns the oxygen in it by combining it with gasoline. If you don't believe me, try bunging up the carburettor so no air can get in. This really improves the gas mileage because the engine won't work and you can't drive anywhere.)

If a tube flashes, it's because there is a relatively long piece of heater wire left uncovered by the white stuff that forms the heater-cathode insulation.

The resistance of tungsten increases with temperature, so if one part warms up quicker than the rest, it will drop more voltage and heat even more, in a vicious circle until it's dropping nearly the full 6.3V and glowing white hot. This is what the uncovered lengths of heater do, because the lack of white stuff reduces their thermal mass. As the rest of the heater begins to warm, the white hot ends dim down and eventually go out.

Some people say that this is deliberate, as it slows the warm-up of the rest of the heater, protecting the white stuff from cracking due to thermal shock. I suspect that Philips just found it difficult to coat the heater all the way to the ends.

[rockon1]

I don't buy the "burning air" thing either.

(To be pedantic, your V8 burns air already, or rather burns the oxygen in it by combining it with gasoline. If you don't believe me, try bunging up the carburettor so no air can get in. This really improves the gas mileage because the engine won't work and you can't drive anywhere.)

If a tube flashes, it's because there is a relatively long piece of heater wire left uncovered by the white stuff that forms the heater-cathode insulation.

The resistance of tungsten increases with temperature, so if one part warms up quicker than the rest, it will drop more voltage and heat even more, in a vicious circle until it's dropping nearly the full 6.3V and glowing white hot. This is what the uncovered lengths of heater do, because the lack of white stuff reduces their thermal mass. As the rest of the heater begins to warm, the white hot ends dim down and eventually go out.

Some people say that this is deliberate, as it slows the warm-up of the rest of the heater, protecting the white stuff from cracking due to thermal shock. I suspect that Philips just found it difficult to coat the heater all the way to the ends.

No,nothing to do with burning air. European manufacturers didnt feel the need to worry about the phenomenom. US manufacters did and built in a slower thermal warm delay time into the design. Bob

[Enzo]

Just don't crack the glass. if the burning air inside the tube manages to get out, it could catch the earth's atmosphere on fire, and then we'd be screwed.

[unparalleled]

Just don't crack the glass. if the burning air inside the tube manages to get out, it could catch the earth's atmosphere on fire, and then we'd be screwed.

You could avert that kind of disaster, just use your Goniometer to track the radioactive "white stuff" from the burning filaments.

[6267]

I read somewhere that 12AX7As and 7025s don't do this, it's just 12AX7 (early US) and ECC83 (euro) valves, something to do with 12AX7A being designed for series string operation. It's most definitely the low initial resistance of the heater. For what it's worth, most of my mullard 12dw7/7247s do this too. Sure makes startup look dramatic !

[tubeswell]

Sure is dramatic - its a little fireworks party when you flick the switch on.

Hey unparalleled, where d'ya get them gonzo meters?

[unparalleled]

Sure is dramatic - its a little fireworks party when you flick the switch on.

Hey unparalleled, where d'ya get them gonzo meters?

How about DC filament supply with slow switch on? Should be simple enough to arrange a 3 pin reg with a capacitor.

Goniometer, google it ( direction finding device. )
(Not for detecting severity of VD)

[wookie winder]

Filament flash or Bright glow

Most Euro made ECC83 tubes do this on power up.

No harm is being done, the filaments just flash or glow bright for a few seconds.
My friend has a few ECC83 tubes in his Hi Fi amp.
They have been inservice and doing this for years in his amps.

I believe they do the same thing in regulated D.C. filament supplies.

NO worries