In a previous discussion I wrote about the following possible problem.
Before using the GI7 and similar tubes to full output, check how the anode
cooler sit on the flat anode tube surface. I have a GI7 for which the anode
cooler is making properly thermal contact with the anode flate surface only
for a very small area surrounding the tube anode screw, and another with
similar, but less prominent such problem. The anode cooler sitting surface
it is not flat.
Put a light source behind the tube an look if the light can be seen between the
anode cooler and its sitting tube flat surface.
You may need to use some sort of heatsink compund there.
Not all of these tubes have this problem.
And about the heatsink compound, from some time, the heatsinks/coolers
for the computer CPU's came with another type of compound, made
(probably) from aluminum powder mixed with some sort of grease.
It is like a silver grease.
Is this type of heatsink compound better than the wide used before white one?
(other than if it touch some surfaces - like the ceramic it is VERY hard to
get it clean again!)
73's,
Traian
"Peter Frenning, OZ1PIF" wrote:
> Said Jim:
> > Max quoted a price of $15. for GI7Bs plus shipping, which is reasonable
> but
> > I'm not going to beat his door down. YMMV, etc. The anode cooler on
> these
> > tubes is not particularly effective for full-output 100% duty-cycle use,
> > and it should be replaced for these applications, or the tube derated.
> > Liquid cooling is a good option.
>
> I agree, I agree, but still... I'm using 1 of these (GI7bT variant, same
> cooler) beasties in my mostly HB 144MHz amp, which has been seeing a LOT of
> 100% duty cycle usage lately (WSJT), and other than having to watch the Ia
> needle and occasionally adjust the tuning, it has been turning out 300W+ for
> hours and hours (30s on, 30s off, I had the lid off a few days ago, and the
> "hood ornament" had become even more attractive! being colored a nice
> blue/violet shade along the edges and corners of the fins...
> The tube still works fine though.
> I also have to admit the it has indeed run away for me a couple of times:
> almost no output, 450mA Ia, and glowing a vivid red in the dark! But again,
> after cooling down, no apparent ill effects!
>
> What it all boils down to: How to get hold of a more suitable anode cooler
> thingie? For me liquid cooling is not an option, and I don't have loads of
> burnt out tubes to take apart for experimenting with reuse of cooling
> fins....
>
> > the cooler. The coolers make a nice Christmas tree or hood ornament.
> They
> > will also fit nicely on a rettysnitch without further modification.
> >
>
> Vy 73 de OZ1PIF, Peter
>
> ********** OZ1PIF **************
> email: oz1pif(no-spam-filler)@get2net.dk
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