I have a Matsushita 12AX7 that every time I power on the circuit where it is connected will cause a flash inside the tube as if it got toom much voltage/current and the filament glows really bright and goes back to normal.
I have isolated it to be a filament thing, because once I give it the filament voltage it flashes briefly.
It does sound normal after that. Is there something wrong with the tube?
I have isolated it to be a filament thing, because once I give it the filament voltage it flashes briefly.
It does sound normal after that. Is there something wrong with the tube?
Thats normal.. I've had tubes do that before too,and it kinda wierded me out..But it's Not a problem.. (I think alot of Mullard and Tele tubes "flash" like that..)
Some Mullard and Philips tubes got same "flash" phenomenon, it seems like it's their characterisitc??
Mr. Stone
Mr. Stone
Excessive voltage ?
Hi Guys,
Did you consider that the tube must be having excessive voltage at the anode ?
On power up , before the tubes turn on , the voltage drops in the power supply components are practically zero and the full dc would appear at the anode . This could be higher than the tube can handle. As soon as it heats up the current will start flowing and the voltage will fall.
You should measure HT voltage at power on and after a while.
Cheers.
Hi Guys,
Did you consider that the tube must be having excessive voltage at the anode ?
On power up , before the tubes turn on , the voltage drops in the power supply components are practically zero and the full dc would appear at the anode . This could be higher than the tube can handle. As soon as it heats up the current will start flowing and the voltage will fall.
You should measure HT voltage at power on and after a while.
Cheers.
Thanks for the info Colt45.
Never seen this happen yet. Strange how it flashes at such low voltage. I assumed it was a white flash like a HV spark that you were talking about.
However if you are refering to the bright orangish flash from the heater , I have seen that in some ECC series tubes.
Cheers.
Never seen this happen yet. Strange how it flashes at such low voltage. I assumed it was a white flash like a HV spark that you were talking about.
However if you are refering to the bright orangish flash from the heater , I have seen that in some ECC series tubes.
Cheers.
Nichrome has a positive temperature coefficient, so if you have a heater wire with a few small sections of smaller diameter, they will hog all of the current for a very short time as they heat up and the resistance increases.
This could be wrong but it sounds as good a hypothesis as any.
This could be wrong but it sounds as good a hypothesis as any.
Tube heaters have a positive temperature coefficient, meaning that they have a lower resistance when cold that they do when hot. This causes a current surge to occur on turn-on, which can make the heaters glow white-hot for a short time. Some claim this shortens tghe lifetuime of the tube.
The "inrush" current can be limited by using a device with a negative temperature coefficient, such as a thermistor, in series with the heater transformer primary winding. The thermistor's resistance is a few hundred ohms when cold, falling to a very low resistance when hot (the opposite behaviour tio a tube's heater).
The "inrush" current can be limited by using a device with a negative temperature coefficient, such as a thermistor, in series with the heater transformer primary winding. The thermistor's resistance is a few hundred ohms when cold, falling to a very low resistance when hot (the opposite behaviour tio a tube's heater).
thanks guys. admittedly i freaked out since this is the first time i've experienced one.
on a similar note, i've owned a NOS RCA 5U4G that after first power on in a circuit gave some "lightning effect" on the top part (ST bottle). i though it was a "welcome, i'm alive" thing 🙂 it was never repeated.
on a similar note, i've owned a NOS RCA 5U4G that after first power on in a circuit gave some "lightning effect" on the top part (ST bottle). i though it was a "welcome, i'm alive" thing 🙂 it was never repeated.
Yes it may, but don't worry about it. The tubes in my uncles 1959 Philips amp do this, and they are still fine (after doing it for 45 years!).ray_moth said:
Best regards,
Mikkel C. Simonsen
If it bothers you (it bothers me- in my gut, I know it can't be good for the tube, no matter what my brain tells me), set up your heater supply to ramp up the voltage slowly for a few seconds rather than dumping the whole thing instantly on turn-on.
hi sy, unfortunately the unit is not mine - it is a TS Audio (Thailand) MM phono stage. but the tubes are mine and I contacted my source to have it replaced.
thanks guys!
thanks guys!
Hi,
Exactly....
The only reason you see the heater flashing is because part of it is not inserted deeply enough into the cathode sleeve.
This was the case for almost any old IDHT tube until the manufacturers decided to fix it as a lot of people considered it a flaw.
Nowadays you still see this on some NOS Eastern-European tubes and the occasional odd-ball.
Nothing to be afraid of, it won't prevent the tube from working properly and won't shorten tube life in any way.
ALL ABOUT HEATERS
THE A SUFFIX SOMETIMES JUST MEANS "CONTROLLED HEATER WARM-UP TIME"
Cheers,😉
Exactly....
The only reason you see the heater flashing is because part of it is not inserted deeply enough into the cathode sleeve.
This was the case for almost any old IDHT tube until the manufacturers decided to fix it as a lot of people considered it a flaw.
Nowadays you still see this on some NOS Eastern-European tubes and the occasional odd-ball.
Nothing to be afraid of, it won't prevent the tube from working properly and won't shorten tube life in any way.
ALL ABOUT HEATERS
THE A SUFFIX SOMETIMES JUST MEANS "CONTROLLED HEATER WARM-UP TIME"
Cheers,😉
hi guys, arnold,
this has happened to me before, remember my phono stage? on my 2 12ax7 (national), they look like light bulbs during turn-on. and like you i was very much alarmed.
solution, since i was using dc for the heaters, i just ramped them slowly - no more flashes! 🙂
regards,
jojod
this has happened to me before, remember my phono stage? on my 2 12ax7 (national), they look like light bulbs during turn-on. and like you i was very much alarmed.
solution, since i was using dc for the heaters, i just ramped them slowly - no more flashes! 🙂
regards,
jojod
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