Mike,
The L4B uses a constant speed blower.? In contrast, the L7 uses a "two speed fan" that accomplishes this task by using a resistor in series with the fan.? When the exhaust temperature exceeds the value on the thermostat, it shorts out the resistor, and the fan goes into high speed (i.e. normal, full 110 vac voltage to the fan).? It will stay in this condition until the temperature drops accordingly. Good luck with the Dentron and thanks for sharing your experiences. Happy New Year and 73s, Evan -----Original Message----- From: Mike Bryce <[EMAIL PROTECTED]> To: [EMAIL PROTECTED] Sent: Thu, 27 Dec 2007 1:31 pm Subject: [drakelist] Soft key and fan controller for HF amplifiers Boys...and girls... I have been working on a old dentron clipperton L amplifier...? after much research and email chatting,I have it up and running. Designed a new power supply pcb for it and it seems to work like it should.. One of the things I was told was the clipperton L is a really solid 1Kw amp and a so so 2Kw amp one thing that get's it goat is that is over heats.. The unit I have has a 390 ohm resistor in series with the ac supply feeding the fan motor. ?Shorting out the resistors puts the fan in high gear. it also makes it a lot louder So... a simple fix here's what I did? Added a softkey that is optically coupled to the radio. Instead of switching 25 volts at 250 ma, the radio only sees 12 volts at 10 ma. The amp is keyed by a high power MOSFET or you can select relay output keying (works with any amp that way) then I added a fan controller when you key the amp, nothing happens but keep the amp keyed a minute or two and the fan kicks up to high speed. after you unkey, the fan will run on high for a while and then drop back to low speed the amount of time will depend on how long you talk! the longer you key down, the longer the fan will run in high speed I don't know if the drake amps use any sort of resistor in the fan lead or not. but... you can always add an extra fan or add a fan to the back of the TRXX series rigs.. it was a fun project? anyone interested let me know mike Mike, WB8VGE SunLight Energy Systems The Heathkit Shop http://www.theheathkitshop.com/ J e e p o|||||||o? Note: No trees were killed in the sending of this message, but a large number of electrons were terribly inconvenienced = ________________________________________________________________________ More new features than ever. Check out the new AOL Mail ! - http://webmail.aol.com
