Fortunately one was used and the other was a rebuilt tube. The filament
went open like a bad light bulb when they failed.
The price of rebuilt tubes has doubled over the past few years. They were
around $1200 with a discount coupon now about $2500. While this sounds like
a very high price, the tube is very capable of 3KW plus at 1296 MHz. If the
filament issue is resolved, one can expect a lifetime of use at amateur
power levels. This makes the $2500 price a bit more acceptable.
So far so good with the relay scheme. That has been in use for a couple of
years now.
73,
Gerald K5GW
In a message dated 8/28/2009 4:04:14 P.M. Central Daylight Time,
jtml@losalamos.com writes:
Gerald, that's unfortunate, I hope you didn't pay list price for those
tubes and have them fail like that.
Your relay scheme seems like it would have prevented problems. Did the
filaments burn out or did they just short to grid and stick there?
73
John
K5PRO
> I lost a couple of good TH347 tubes due excess filament current at turn
on.
> I thought there was sufficient turn on current limiting but apparently
> not.
>
----
> 73,
> Gerald K5GW
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