[Amps] running redlined

["John T. M. Lyles" <jtml@lanl.gov>]

Ed, N1TS, was certainly on target in his thorough explaination about 
the facts of running red or orange anodes in glass triodes and 
tetrodes. In some very old data sheets from Taylor tubes I have seen 
reference to the use of Graphite anodes that should not be run red. 
Typical modern glass tubes like the 3-500Z almost always run with 
some slight color, in 'econonically' engineered systems. Obviously 
one could design a system to run with 50-100 watts of dissipation in 
these tubes and they would look grey/black inside. Not necessary 
though, since they are capable of running orange in service. As long 
as the cooling is there for the seals, most important.

One more link to add to Ed's already excellent collection is this one 
from E2V, the former English Electric Valve/Marconi company.  Check 
the link on lifetime improvements.
http://e2vtechnologies.com/technical_notes/grid_tech_notes.htm

I remember seeing 833s in a Gates BC500H TX on 1250 KHz when I was a 
kid. The engineer (ham) told me that he would adjust the idling bias 
to set the current in the modulators and roughly the color of the 
anodes. It was impressionable to me.

In the Continental 314R1 that I am restoring for AM service, there 
are three 3-500Zs. They are all Amperex. The two in the RF side 
(paralleled) show no color at all with 1 kW into Dummy Load. But the 
switch tube (running 70 KHz PDM with audio) runs orange. When I first 
fired it up, the clamp diode was shorted on the PDM output, and that 
tube came on with 8 kV across it into a dead short. Should have seen 
the color, almost like a white light bulb. Also lots of blue streaks 
on the glass from the beam. It survived the momentary event (5 
seconds), and is now running fine.

When making tubes, anode color is sometimes used to indicate 
temperature during processing. Final exhaust of large (w/handles) 
tubes is done with high internal temperature to bake out the 
molecules of gas, before pinching off the seal.

73 and happy holidays
John
K5PRO



> Some tubes are made to exhibit red color under maximum CCS or ICAS ratings.
> The transmitting tube datasheets often contain text such as  "the plate
> shows a dull red color at maximum CCS ratings", or "The plate shows a bright
> cherry red color at maximum CCS ratings" or even "shows an orange read color
> at maximum CCS ratings".  For, some tubes description says "the plate shows
> no color at maximum ratings".
,,,,

> My own advice would be, use the amp, enjoy it. The more you read about
> obscure failure modes, the less you'll enjoy it. ;-)
> 73s
> Ed
> N1TS

right on.
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