Tubes Asylum

Mortality rates for National Union 6F8G/VT-99 tubes

70.15.83.60

Zebra_Finch

A

greetings,

I have been using the venerable National Union round-plate 6F8G tubes
in my integrated amp (Cary CAD-300SEI). I have had 2 spectacular driver
tube failures, where there were literally fireworks in each bottle.

Both tubes had maybe 200 hours on them before they both died.

Is there an intrinsic problem with the National Union 6F8G?

I have rolled many 6SN7 tubes in this integrated amp and never had
problems like this.

I would be interested if other folks are having problems with this
specific tube.

david

Follow Ups:

RE: Mortality rates for National Union 6F8G/VT-99 tubes - Sondek 12:07:38 04/16/17 (0)
I used to use them as drivers in a Counterpoint NP100. Never had an issue with them. A really excellent sounding tube. Those and the GG NU 6SN7s might just be my all time faves.
RE: Mortality rates for National Union 6F8G/VT-99 tubes - DAK 10:20:46 04/16/17 (0)
If your amp should be running 6sn7gtb tubes then the plate voltages could be 350 to 450vdc. The 6f8 has a max plate rating of 300vdc with a recommendation of 250vdc. You should check your amp's voltages before running those tubes. Sometimes when a tube fails it takes out associated components. You might be pushing your luck.
RE: Mortality rates for National Union 6F8G/VT-99 tubes - FenderLover 18:45:59 04/15/17 (1)
Maybe, the setup is bit too hot for those tubes? I noticed that units which run input, gain stage, phase inverter hot often get premature noisy and failures in those tubes.

Just a thought...
- RE: Mortality rates for National Union 6F8G/VT-99 tubes - Mechans 18:10:11 04/18/17 (0)
  OP, I would also check the integrity of the adapter unless you are not experiencing problem with other6F8Gs.

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