Jim Barber wrote:
I have several Eimac 8877's I bought as tested new-equipment pulls
around 5 years ago. I tested them again myself at the time, then packed
them away.

Here it is 5 years or so later. The question for the panel is how long
should I "cook" the filaments before putting plate voltage on?

Thanks,

Jim, N7CXI
I don't think that the tubes will go bad just sitting on the shelf for 5
years, they should work the same as the last time they were used.
Having said that, it is always a good idea to wait until the cathode
reaches full emission before applying plate voltage and rf drive.

I would think that these tubes reach that point within a minute of
applying filament power. You could apply filament power to the tube on
the work bench and monitor the tube temperature. With the tube out of
the socket and heater power applied via use of heavy clip leads you can
feel the base of the tube with your hand and see how long it takes to be
able to feel the cathode heat reach the outside of the bottle. (It
won't be hot, just luke warm).

Thanks.

I wasn't concerned about them going bad per se, just tiny bits of gas
released from the inside not getting 'getted' and causing a flashover
when plate voltage is first applied after long-term storage.

It seems that any time I fire up an Eimac ceramic triode after it's been
sitting a long time it flashes over once just to spite me and stress
the supply. Maybe it's just bad luck or other operating practice on my part.

Jim, N7CXI


ken scharf wrote:
Jim Barber wrote:
I have several Eimac 8877's I bought as tested new-equipment pulls
around 5 years ago. I tested them again myself at the time, then packed
them away.

Here it is 5 years or so later. The question for the panel is how long
should I "cook" the filaments before putting plate voltage on?

Thanks,

Jim, N7CXI
I don't think that the tubes will go bad just sitting on the shelf for 5
years, they should work the same as the last time they were used.
Having said that, it is always a good idea to wait until the cathode
reaches full emission before applying plate voltage and rf drive.

I would think that these tubes reach that point within a minute of
applying filament power. You could apply filament power to the tube on
the work bench and monitor the tube temperature. With the tube out of
the socket and heater power applied via use of heavy clip leads you can
feel the base of the tube with your hand and see how long it takes to be
able to feel the cathode heat reach the outside of the bottle. (It
won't be hot, just luke warm).