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[AMPS] 4CX1500A in grid driven AB1 for Ham radio

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Subject: [AMPS] 4CX1500A in grid driven AB1 for Ham radio
From: (Rich Measures)
Date: Thu, 22 Jul 1999 10:33:14 -0700

>Hi guys from the Netherlands !
>I have several used Eimac 4CX1500A which have run between 7000 and
>15000h in a mediumwave commercial broadcast transmitter of the 100kW
>class to drive the final watercooled final.
>Now I like to use these 4CX1500A in a single tube grid driven linear amp
>for Ham radio. I have the original data sheet from Eimac and already a
>lot of theory information (as well as the very good suggestions from
>AG6K's webpage)
>What really is missing are some ham's who really have practical
>experience with the 4CX1500A. Obviously this tube is totally different
>than the famous 4CX1500B (Bravo).
>However (probably because of the price ?!) I have never found anyone in
>EU, who has some practical experience with 4CX1500A (Alpha)
>for example:
>* the data sheet shows 1A at 5kV as maximum rating. 

? Only for Class C  (where anode dissipation would be minimal) .  For 
Class AB1, using AØ emission, the rating is 4kV. 

>How high is the peak
>current when the grid is driven to almost 0V just before grid current is
>starting to flow ?!

? According to the Eimac data sheet, using 750v on the screen, 4.0a-peak. 

>* what will be the approx. power output in amateur radio service ? Can I
>expect more output than Eimac datasheet, if considering (speech
>processed) SSB or CW for contest operation ???

?  If you use SSB/CW, have 20mm of manometer indication,  and you tune-up 
with 50wpm dits, my guess is that you could use a 5kV anode supply.  With 
4.0a-peak emission, and 750v on the screen, a healthy 4CX1500A ought to 
be able to make about 3700w PEP.  

>* are there any other suggestions for such a project to use this or very
>similar power tetrodes ???
>* any suggestions to minimise the fan noise (without minimise the
>airflow itself... hihihi)
?  A cooling problem with the 4CX1500A (and 4CX3000A) is extra noise 
caused by Eimac's use of verticillated cooling fins instead of using 
straight cooling fins.  .  .  When high pressure flows through a 
verticillated-fin anode cooler, it generates a sound like wind blowing 
through pine trees.  With my 4CX3000A amplifier, the noise from the anode 
cooler was so loud that I decided to install sound absorbing baffles in 
the output compartment.  This is why I recommend using a tube with 
straight cooling fins, like the 8171. 
 {note -  verticillated cooling fins have a protrusion that causes whorls 
of cooling air to form as air passes through the fin.  Whorling increases 
heat transfer.  However, more air pressure is required.  More air 
pressure equals more noise.) 

-  good luck, Ulli


R. L. Measures, 805-386-3734, AG6K,  

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