Home » VintageKustom.com » Comment Board » Cooling Fan a good idea to run K100 at 4 ohms?
Cooling Fan a good idea to run K100 at 4 ohms? [message #2686] Sun, 27 April 2003 16:01 Go to next message
LesS is currently offline  LesS
Messages: 477
Registered: December 2002
Senior Member
The K100 head is designed for use at 8 ohms and will put out about 60 watts RMS. Both my K100C-8’s had 8 ohm speakers wired in series. So the amp is putting out about 30 watts at the 16 ohm load but could put out somewhere between 70 to 90 watts if I chose to risk running them in parallel (4 ohms). According to the website postings, some people are running the K100’s at 4 ohms with no problems, while others still advise against it. (My oldest K100C-8 (approx Sept 1969) has a speaker output jack on the back panel (appears to be factory installed) but the newer ones don’t). Has anyone tried mounting a cooling fan inside – it would fit easily since I am using it with the reverb pan out. -Les Strickland
Re: Cooling Fan a good idea to run K100 at 4 ohms? [message #2687 is a reply to message #2686] Mon, 28 April 2003 07:46 Go to previous messageGo to next message
stevem is currently offline  stevem
Messages: 4728
Registered: June 2004
Location: NY
Senior Member
Hi.A fan is a great idea for any amp, but even more important on a soild state amp as you drop the output impeadance and raise the output wattage. A K100 can run with a fan at 4 ohms but the circuit will not sound as good stock, as at 8 ohms, probibly more so if your playing bass thru it near its max output wattage, As you said running at 8 ohms will give you double the output wattage, but the amp will no be twice as loud. What you will have is a puncher amp with twice the amount of clean head room before the amp starts to distort.You would all most have to quadrouple the wattage or the amount of speakers to get get a doubling of the acoustic wattage, which is what the ear senses.If you put a fan in run it off a seperate power cord, and clear silicone glue it to the amp.You do not need a very large one, as the amp uses the hole chasis as a heat sink for the two output transistors.One thing you need to watch out for with a fan, if you live in a humid area, is the mosture that will stay in the amp after you turn it off since you are moving alot more air thru it. Keep a eye on it.
Re: Cooling Fan a good idea to run K100 at 4 ohms? [message #2688 is a reply to message #2687] Mon, 28 April 2003 09:29 Go to previous message
C4ster
Messages: 686
Registered: June 2001
Location: Mukwonago, WI (Milwaukee...
Senior Member
I am one of the typing heads who does not approve of running K100's at 4 ohms. (Here is the overtechnical B.S.) The emitter resistors are too large to run at a 4 ohm load. The voltage drop across these resistors cause too much negative feedback into the differential amplifier. This causes instability problems and increased crossover distortion. It won't hurt the amp, but you WILL hear the distortion as your notes sustain out. It is not very melodic. Sorry about the tech talk. Conrad
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