Simple solution to the noise problem: use a closed air handling system
(pipe air in and out) and remote the blower.
-----Original Message-----
From: Rich Measures <measures@vc.net>
To: ulli@wxs.nl <ulli@wxs.nl>; Amplifiers for Ham radio
<amps@contesting.com>
To: <amps@contesting.com>
Date: Thursday, July 22, 1999 1:34 PM
Subject: Re: [AMPS] 4CX1500A in grid driven AB1 for Ham radio
>
>
>
>>
>>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
>
>
>Rich...
>
>R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
>
>
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>
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