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Re: [Amps] TH347 filament ramping

To: jtml@vla.com, amps@contesting.com
Subject: Re: [Amps] TH347 filament ramping
From: TexasRF@aol.com
Date: Fri, 28 Aug 2009 17:33:18 EDT
List-post: <amps@contesting.com">mailto:amps@contesting.com>
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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