[Premium-Rx] Premium-Rx Digest, Vol 51, Issue 4

[jensoz8so]

Hello all...


I have been working on these amplifiers for the last 15 years and 
restored about 10 of them. The noise from the internal fan is quite 
annoying. I measured the noise level on an unmodified amplifier as 78 
dBA at a distance of 70 cm. Then I added an outside silencer similar to 
the one used by VK5ABN. This reduced the noise to 70 dBA – still way to 
much!

The internal fan is intended to remove 3500W off heat when the amplifier 
is delivering 1kW of output and the inlet temperature is +50°C and the 
SWR is far from optimum, the supply voltage is down by 10% and the 
amplifier gain is down at 37dB!

And although I agree with Scott in his general observations, I think 
there is room for some reduction in the necessary airflow if we modify 
the operating conditions. It can be found that the outlet temperature 
should never exceed +90°C in the original operating conditions.


If we respecify the operating conditions to nominal mains voltage, SWR 
less than 1:1.5, the inlet temperature to +25°C, then it would be fair 
to say that the heat removal does not have to be greater than 1000W (50% 
efficiency) This makes a big difference in the required airflow. I 
calculated 149m3/h compared to the original 238m3/ h. The 149m3/h is 
equivalent to a velocity of 2m/sec at the amplifiers outlet.

I removed the internal 400Hz fan and fitted a 4” flange to the front of 
the amplifier. An external fan is now installed in the attic and ducted 
to this front flange with traditional AC ducting materials – The last 
piece being a flexible hose so that I still can operate the amplifier 
drawn out on the slides.


If you want to try out this arrangement, you will have to increase the 
size of the van on the airflow switch. Dont leave it out of circuit! It 
takes about 20 minutes to melt the chimneys to the tubes, and 
approximately 2 hours to chop them apart again, not to mention the time 
needed to replace the chimneys (The tubes survived!)

I have used this arrangement for years now, and considering that the 
amplifier is intended for 24/365 operating RTTY and only being stopped 
for tube replacement, I think this is OK for ordinary amateur 
operating.When adjusted according "to the book" (1250W PPC, 1000W APC) 
it delivers 1kW of CW output and 1500W PEP in SSB.

To keep the current consumption down, I always have my amplifiers tuned 
up to minimum 43dB of gain (50mW for 1000W out)

One final word about cooling. The RF-124 PSU has a 100W bleeder resistor 
that very much like cooling! It is expected to have one end fixed to the 
chassis, and the other end floating/sliding. If you tie up the right end 
of this resistor preventing it from thermal expansion it will explode, 
and this is an chocking experience...!

My final noise level is now below 40 dBA - even with the PA just below 
my operating desk.

73
Jens/OZ8SO





Den 12-02-2011 18:00, premium-rx-request at mailman.qth.net skrev:
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> Today's Topics:
>
>     1. Thermal Management Issues/Remote Operation in the UK
>        (John P Ceresole)
>     2. Fan Noise (Tisha Hayes)
>     3. Re: Fan Noise (W2HX)
>     4. Fw: Fan noise (Michael O'Beirne)
>     5. Re: Harris 110A 1 kwatt rf Amplifier question (Steve Sykes)
>     6. Re: Harris 110A 1 kwatt rf Amplifier question (Steve Sykes)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Fri, 11 Feb 2011 16:55:42 +0000
> From: John P Ceresole<veloce at tcp.co.uk>
> Subject: [Premium-Rx] Thermal Management Issues/Remote Operation in
> 	the UK
> To: Premium-Rx at mailman.qth.net
> Message-ID:<20110211175938.94F0024404D at smtp2.sst.tcp.net.uk>
> Content-Type: text/plain; charset="us-ascii"; format=flowed
>
> Hi List Members
>
> Was interested in Berndt Josef Wulf's predicament - well
> unfortunately I have to agree entirely with Scott Schappert's
> view.  Problem is (to re-iterate) is that quite a lot of kit now
> coming onto the second hand market was designed with the military in
> mind and the military does what it's told and has to endure whatever
> discomfort is thrown at them.
>
> I recently did some work on a (very new) transportable satellite
> system whose screeching HPA fans were unbearable 10 metres away!!
>
> I also worked with radios designed for use in audibly quiet
> environment which had 4 fans in them - and whilst new they were
> reasonably quiet but as soon as their bearings assumed a bit of play
> during use, they became quite noisy.  I am glad to say that the
> follow on equipment was much quieter and only had one fan.
>
> Has anyone considered using contact cooled valves and liquid thermal
> transport?
>
> I am thinking here of the 4CX-250B tetrode and it's contact cooled
> variant type of thing.  BTW I am no designer of such kit but have
> seen it in use which might get round Berndt's dilema.
>
> Has anyone got experience of remotely operating equipment - I am
> thinking receivers here remotely sited away from sources of
> interference such as telephone line ADSL and PLT and all the other
> sources of noise that are increasingly polluting our airwave
> environment such as Solar Panel Inverters (suddenly becoming very
> popular in the UK?  Transmitters similarly as Berndt relates in a
> block of flats will be anything but popular so remote operation
> becomes the only way to successfully pursue our hobby.
>
> Any pointers greatly appreciated
>
> Best wishes
>
> John G8BSD
>
>
> ------------------------------
>
> Message: 2
> Date: Fri, 11 Feb 2011 11:25:16 -0600
> From: Tisha Hayes<tisha.hayes at gmail.com>
> Subject: [Premium-Rx] Fan Noise
> To: premium-rx at mailman.qth.net
> Message-ID:
> 	<AANLkTimpMX2VNmXpo4h+MWE0aOhH-rc+EA4ssQ+XXJvE at mail.gmail.com>
> Content-Type: text/plain; charset=ISO-8859-1
>
> You can try to run the fan when it is removed from the transmitter. Some
> designs are just "screamers", usually this is due to the blade design but I
> have run across some with very noisy bearings. A good example of a loud fan
> is what is installed in the Harris RF-350K power supply deck. Many of those
> suffer from bearing problems.
>
> If you can find the right fan frame size you may run across a fan that will
> give you the same CFM and pressure rating as what you are using now. When in
> doubt, go higher.
>
> In my console I use eight additional 120 VAC fans to keep the air
> circulating for the tube based equipment. This is in addition to the fans on
> the RF-350K's and the Harris 500 watt amplifier. I recently ran across some
> 48 volt fans that put out a much higher CFM, even when running them off of
> 24 VDC. As I climb through the console I am replacing the AC fans with the
> DC fans one at a time. I even stuck a fan onto the RF-590 just to blow air
> through the chassis.
>
> I have a "break glass in case of emergency" type thermostat in the console
> so if the internal temperature rises above 120 F the fans that are running
> at 24 volts will cut over to full power, 48 volt operation. On the power
> control panel I have a latching relay tied to a switch and an LED to alert
> me that the temperature was exceeded at some point when I was not around. I
> never power down the console and some of the radios are operating in an
> unattended mode or across a remote Ethernet link (ROIP (radio over IP) and a
> digital control channel).
>
> I added a duct that pulls air out of the crawl space and goes into a turbine
> fan that came off of a high voltage switchgear cabinet (VERY NOISY and draws
> about 5 amps at 120 VAC, good thing it is mounted under the house). Since it
> is usually in the 50's and 60's down there (even in an Alabama summer) I can
> blow air up into the console for rapid cooling.