Grid leakage in 6CA7
On Jan 28, 5:33*pm, diamondsouled wrote:
There is a way of waking up the getter flash in tubes such as this, it
is actually quite common in Tung Sol 6550s for them to test gassy/grid
leakage. Some people have built rigs where they can put enough voltage/
cuurent into the tube, gradually, that in will activate the getter
flash. Here's an alternative method that can work:
Here's how to bake one:
1. Put the cold tube(s) in a COLD oven; set the oven thermostat to 300
F.
2. Bake the tubes for 4-5 hours at this temp.
3. Turn the oven off and walk away. Don't peek! Let it cool very
gradually.
4. When the oven is completely cooled take the tubes out and retest.
They will likely be fine as the getter will have absorbed gas
molecules - but...
DO NOT SKIP THE RETEST!!
Some tubes may have some cathode poisoning too - the baking may help,
but just heating the cathode is often enough to remedy the situation.
For that a tube tester is fine - but you don't know what's going on
inside the tube so it's best to be safe. Let them sit in the tester
while after the baking process is complete, don't rush. .
Of course if there is little or no getter flash left there might be
nothing left to activate. ;^)
Cheers
Larry
I hope it's not a silly question but how does baking the tube differ
from running the heater for an hour or two? You could even wrap the
tube in a cloth to get it hotter - be careful! Or just run it at a
modest plate current for a while.
Cheers,
Roger
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