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

[black_labb]

in my old holden/wasp amp 1 of the 12ax7's filament will have an intense glow as the heater is turned on, and settle to the normal glow after a second or 2. all other tubes slowly start to glow over a couple seconds, but this one is instantaneous and much brighter than usual (but only for a short period). i repeat, the intensity is only for a moment, and it returns to normal over the next second. it is only one tube

any explanation for this? is it a bad thing? is it maybe a different material used for the filament which reaches the operating resistance once heated (as resistance rises with heat)?

[Enzo]

SOme heaters do this.

[black_labb]

thanks, i was a bit worried, as there are 3 of the same tube type in the amp, and only one does this.

[Sweetfinger]

This comes up every once in a while here. Some tubes were designed for a faster turn on in TV's, radios, etc. Those are the ones that 'flash'. Usually there's no clue on the box or tube if it is fast or slow, just plug in and watch.

[andrew_k]

black_labb: I don't suppose this was with an Aus made tube was it? I was having the same thing happen with an old AWA Radiotron 12AX7 today and it freaked me out!

[Steve Conner]

I've seen quite a few preamp tubes that do this. I don't know why it happens, but it doesn't seem to cause any harm.

[black_labb]

black_labb: I don't suppose this was with an Aus made tube was it? I was having the same thing happen with an old AWA Radiotron 12AX7 today and it freaked me out!

was a miniwatt, another aus tube but not a radiotron.

[TD_Madden]

all my Phillips 12AX7s do this.

[unparalleled]

in my old holden/wasp amp 1 of the 12ax7's filament will have an intense glow as the heater is turned on, and settle to the normal glow after a second or 2. all other tubes slowly start to glow over a couple seconds, but this one is instantaneous and much brighter than usual (but only for a short period). i repeat, the intensity is only for a moment, and it returns to normal over the next second. it is only one tube

any explanation for this? is it a bad thing? is it maybe a different material used for the filament which reaches the operating resistance once heated (as resistance rises with heat)?

Lots of info on your amp on (Google) " anz amps".
Your heater glow is quite normal.
Does your Wasp still have 4 preamp valves?
Quite a few of them were severely modded to only use two valves, I have just completed a complete restoration on a 200 Wasp.

[black_labb]

Lots of info on your amp on (Google) " anz amps".
Your heater glow is quite normal.
Does your Wasp still have 4 preamp valves?
Quite a few of them were severely modded to only use two valves, I have just completed a complete restoration on a 200 Wasp.

i've been on the anz amp site a fair bit, its a great resource. was going to send in a schematic of the wasp amps, but i lost the diagram i was doing and need to redo it. i've got 2 200w wasps, one XL and one VBL. both have 4 6550's. great amps. i changed a coupling cap and cathode bypass cap on the xl as they were pretty small, making the amp a bit too bright.

which one did you restore? any pics anywhere? did you change the electrolytics? i've been meaning to do that, but they seem to be fine.

[unparalleled]

i've been on the anz amp site a fair bit, its a great resource. was going to send in a schematic of the wasp amps, but i lost the diagram i was doing and need to redo it. i've got 2 200w wasps, one XL and one VBL. both have 4 6550's. great amps. i changed a coupling cap and cathode bypass cap on the xl as they were pretty small, making the amp a bit too bright.

which one did you restore? any pics anywhere? did you change the electrolytics? i've been meaning to do that, but they seem to be fine.

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.

[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 are some photos of my work online: Google "guitar amplifier repairs howick"
You will find my local Trade and Exchange (online newspaper) work wanted adverts.

[rockon1]

all my Phillips 12AX7s do this.

Yep Philips and other Euro pre amp tubes will flash. Totally normal.

[SteikBacon]

My old teacher explained this that the valve wasn´t 100% completly sealed and burned air.

[unparalleled]

My old teacher explained this that the valve wasn´t 100% completly sealed and burned air.

Interesting theory, my understanding is that air does not burn.
Wish I could get my old V8 to burn air!
If there was air in the tube the silver coating on the inside from the getter would oxidize and the tube would turn white.
The filaments are designed to handle the inrush current on switch on.

My old employer used to fill out service sheets " Replace rectumfire valve and tune for maximum smoke"