826 triodes vs. senility

[K1ZJH]

I remember playing with a stash of NOS 826 triodes back in the sixties (wanted to make an AM amp for my Twoer--never happened.)

Anway, I recall that when I tried powering up filaments on the first two tubes they immediately went open. The ones I slowly brought up the filament voltage on survived.

Was this the luck of the draw, or did these tubes require some sort of filament conditioning after being in storage for 20 years?

Just curious...

Pete

[W7TFO]

Not so much conditioning as using a high-reactance filament trans or soft-start.

Most TX fil trans had an adjustment rheostat (not a variac) in the primary to achieve this.

Modern bench supplies have a very low source impedance and can pop a filament instantly due to the current inrush.

Also, if those tubes were used, the filaments get very brittle and easily die from the thermal shock of lighting them up full bore.

73DG

[The Slab Bacon]

I used to have a pair of Gonstipated amps with them. Each had 2 in shove-yank. (one for 6m and 1 for 2m) They were very persinckity to come up with good spares. I ffound bunches of them at hamfests, but few had survived storage very well. I went through dozens to come up with a couple of good ones.

They either were damaged from shock (broken filaments or plates broken from supports) OR....................

The seal had lost it's seal and they were airbound or gassy. The ones that had lost all of their vacuum would let off yellow smoke inside the bulb and frost up the glass when lit off.

Due to the fact that they are a very fragile tube I would shy away from using them in anything. Electrically, if you get good ones they are hard to kill, and happy to run along all day with the plates lit up as bright as the filaments.

[Opcom]

The ones that had lost all of their vacuum would let off yellow smoke inside the bulb and frost up the glass when lit off.

Christmas ornaments!

[The Slab Bacon]

The ones that had lost all of their vacuum would let off yellow smoke inside the bulb and frost up the glass when lit off.

Christmas ornaments!

or target practice   

[KB2WIG]

or send 'em to that guy in France that makes his own tubes.


klc