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Author Topic: Cooling SB-201  (Read 1348 times)
AE6RF
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« on: April 08, 2007, 12:41:46 AM »

Hello all,

Finally got to to participle in my first RTTY contest running power. 500+ Watts (as opposed to 100W) makes running a frequency marginally more productive.

Anyway. The amp gets warm... really warm... when "running."

I've got the drive dialed back so the amp is only putting out about 500W, but it still gets plenty warm on top.

Would it help to add a muffin fan? If so where?

Thanks & 73 de Donald
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KA5N
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« Reply #1 on: April 08, 2007, 01:47:46 AM »

RTTY has a 100% duty cycle when transmitting.  The SB201 isn't designed for this type operation.  The best bet would be an amplifier which can take the gaff.  Harbach Electronics sells a replacement fan with larger blades which provides marginally more cooling.  To get much more cooling would require provision for better "breathing" i.e. getting more air through the amp.  The major heat producers are the tubes and the transformer.  Since air flow depends on convection as well as forced air (fans) one has to be carefull not to install an extra fan and inadvertently block the air flow.  
Best bet is to get an amp stout enough for "brick on key" operation.
Good Luck Allen
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K6AER
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« Reply #2 on: April 08, 2007, 07:26:15 PM »

The 572B’s in your amplifier are only good for 160 watts each with proper cooling. That is 320 watts CW, FM or RTTY with the best cooling available.  The SB-200-201 amplifier was designed for Morse CW (50%) duty cycle or SSB (20%) duty cycle. If you want to run RTTY, I would suggest using a ceramic tube amplifier which has a much high duty cycle and more efficient cooling.
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KI4NX
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« Reply #3 on: April 09, 2007, 07:19:08 AM »

I use the SB-200/201 daily. However, it's only for SSB use. I added two muffin fans using wire wrap to keep them together. I place them on top of the amp just above the tube compartment and have the air flow drawing warm air out of the amp. I used an independent 12V supply to power the fans. I turn on the amp and then turn on the fans. I plan on connecting a relay to the internal power to switch the fans on when the amp is turned on; however, that's a summer project.

GL with your amp,
Ken, KZ4Y
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