GK fan replacemant, puzzled about DC volts

[Mad Tango]

I have a GK backline 600 practice amp that the colling fan went out. The orginal fan is 24 volts dc on label. I can find a direct GK replacement fan that also varifies the 24 v DC input voltage for my model. However; when I measure the DC volts at PC board output two pins (W/fan disconnected) it is 60 volts DC. I realize that the fan load/resistance will drop some of the volts when connected, but from 60 to 24volts- thats a big drop needed. I was wondering if the way the amp might have been wired, do I need a 48 VDC fan. Anyone here ever replace a fan?

[craig.p]

Switch your meter to AC volts and measure again. If you get a reading, that may provide a clue as to what's going on.

[Mad Tango]

OK, I'll check It will about 5 min to do this.

[Mad Tango]

I get 0 volts ac

[fdeck]

It may be 24v under load.
Still, to be safe, it's best to contact gk.

[Mad Tango]

Also, I forgot to mention that now I realize the fan never worked when I bought it about 3 months ago. This is my first GK and I thought it was air cooled because its an entry level GK amp. I noticed it had that hot electronic smell. I had to look closely into the small vents and see the fan inside. I am wondering if the fan got blown up right away w/mismatched voltage.

[B-string]

There is a 24Volt zener diode that falls out of circuit with the fan disconnected. 24Vdc fan is correct.

[B-string]

Originally Posted by Mad Tango

Also, I forgot to mention that now I realize the fan never worked when I bought it about 3 months ago. This is my first GK and I thought it was air cooled because its an entry level GK amp. I noticed it had that hot electronic smell. I had to look closely into the small vents and see the fan inside. I am wondering if the fan got blown up right away w/mismatched voltage.

The fan is only supposed to come on when needed to lower heat sink temp. It does not run all the time.

[Mad Tango]

Thanks for the info. I just ordered a $3.95 fan that fit ALL the requirements besides 24 VDC (size, amp draw, RPM etc.) of the orginal Jamicon fan on E bay so I won't be out much if it doesn't work.

[sconix]

The fan is the load off of a variable regulator. The source is 60 volts but there is a 24v zener limiting the output v under load. A temp sensor at the bottom of the circuit varies the ref with temp.
At least that's what it looks like to me. There maybe a different explanation. The amp calls for a 24vdc 160ma 80x80mm fan. Unless Q28, Q29 the 24v zener or temp sensor are bad, you should be good to go.

[Mad Tango]

Thanks to all!!- for the quick and informative responses. The fan by it self reads open ohms, hope it its JUST the fan. Now, I feel better that it does take a 24 volt fan.

[fdeck]

Originally Posted by Mad Tango

Thanks to all!!- for the quick and informative responses. The fan by it self reads open ohms, hope it its JUST the fan. Now, I feel better that it does take a 24 volt fan.

Two or three 9-V batteries in series should be able to run the fan just briefly to see if it works.

[two fingers]

Originally Posted by Mad Tango

Thanks to all!!- for the quick and informative responses. The fan by it self reads open ohms, hope it its JUST the fan. Now, I feel better that it does take a 24 volt fan.

Doesn't take but a minute or two around here. Awesome.