SWR 350 redhead 1997 schematic? Fan is dead

[stevesamps]

Hi

I was hoping for a little help with this one, anyone know how to get a schematic for the bass 350 SWR redface amp?

or how they power the fan, I did a little test this morning.

I removed the 24V fan and tested with a PC power supply 12v the fan is not "bad" it spun with the computer supply.

I could not see any voltage being applied to it in circuit.
IT is the same size as a 12V computer fan, I was just looking for
a way to fix this quickly as this is a guy with gigs coming up fast.

The amp is fine I think the driver circuit has failed somehow
I was tempted to make my own 12v rail and use the PC case fan

anyway thoughts and Ideas appreciated.

This amp has a "fan defeat" switch, perhaps I should read that again
does that mean its still based on thermal temp until the fan will go on?

This guy says it never went on, and he is concerned about it.
He also mentioned he wants to be able to kill the fan for recording.

I guess I am wondering if the fan will engage with the amp cold
based on the switch, or if there is more to it than that.

Steve

[Enzo]

Hmmm...

I got Bass 350, I got 350x, I got Redhead, and I got SUper Redhead. I don't see 350 Redhead.

On the Bass 350, the fan is simple, there is a series thermal switch. The fan would come on only if the heatsink gets hot enough. SOme other models had a series resistor with the thermal switch across the resistor. SO when cold the resistor slowed the fan. Once hot, the thermal switch shorts across the resistor for full speed. In that case, an open resistor would kill slow speed.

[stevesamps]

I tried to reply earlier..

anyway I think its the thermal switch that is open

I ordered one but It is the 50C not the 90C
part number oops...

but maybe in a good way thats 122 degrees vs 190
and thats all the way out at the edge of the heatsink
so worst case he will have to turn off the switch more often..

This is the bass 350 model

does that part number cross over to anything like NTE?

67F040

I found the 67F050
and I have one coming

[Enzo]

There is the Bass 350. I threw in the later power amp, but that seems to be after yours was made.

Got a heat gun? Hit the thermal sensor with it to see if it trips.

[stevesamps]

Thanks so much Enzo you rock as always

[jp3zone]

Enzo, could you please advise on the bias voltage settings for the WM4004. Im replacing the whole poweramp pcb module, but it comes without the output trannies, so I have to install a set.

Thanx!

[stevesamps]

The fix was the thermal switch

Just for the record I installed the little two leg critter
the replacement I found actually spins up the fan
sooner, like 124 degrees as opposed to 194!

perhaps that will keep the whole thing a bit cooler
I found the part on ebay last two digits were 50 not 40 like the
original.

just FYI

and Thanks

[Enzo]

Bias is set by applying a sine wave, scoping the output and adjusting bias for where crossover distortion just disappears. Or we use the mains current drawn by the amp and run the bias up from cold until just the point where cirrent draw starts to increase, then back off a hair.

I don't use voltages to set biases on SS amps. If there is some specificed test point voltage, whatever information I have is what is on the schematic.

[Prairie Dawg]

I just finished up some work on one which included replacing a very noisy fan. As part of that I did an extended temperature survey to make sure everything was working right. The manual says the temperature switch triggers at 50 deg. c and opens at 40 deg. c. The surface temperature of the heat sink gets pretty hot but the exhaust air temperature measured with a Fluke digital thermometer runs at between 41 and 42 deg. c. It heats up fast, so I advised the owner to keep the fan on always and consider hard wiring it.

[jp3zone]

Cool, thanks, I'll run her on the scope and adjust for minimum distortion.

[heribertogj]

hello, good night!

I'm new here and I would like someone to help me solve a problem with a blue tablet 350 redhead, I can not run the fan in the diagram 350 Power Bass Amp Module and BOM (Board Blue Version). Pdf says connected to the headers 6 (-) and 7 (+) but this does not give me any terminal voltage only when taking v-as common but I get 75 volts this measurement, the fan can work 24 volts with 75, and happens to the capacitor 1000/35volts,

The settings in the header is as follows:

1 2 3 4 5 6 7 8 9
V- SPK THERM OUT GND IN IN GD AC V+

thank you very much for your attention.