Ampeg SVT-3 Pro fan?

[drewl]

Hey I forget, is the fan supposed to run at all when this amp is turned on,
or only when it warms up?

It's got about 16v DC on it at startup, on a 24v fan which I assume is the stock Rotron unit.

[Jazz P Bass]

The schematic shows an LM35 temperature ic (TS1) driving an NPN transistor (Q16), which turns 'On' the fan.
The LM35 is a really cool ic.
The output voltage versus temperature is very linear.

So unless there is more than 0.6 volts on the base of Q16, no fan.

[drewl]

The manual says the fan will run slow at power up then increase speed with heat.
everything in the fan circuit tests okay in circuit.
16v on a 24vfan at power up seems about right.

Pull the fan plug and you get the 65v supply across the plug pins.

[g1]

With 16V on the fan, I would expect it to be moving somewhat.

[The Dude]

^^^^ Agreed. Apply 24 (or so) volts with an external supply to the fan and see if it works. I'll bet not.

[Jazz P Bass]

So if the fan is not there or open circuit, the tubes do not get heater voltage?
Tricky if true.
Though it doesn't help if the fan has continuity & still doesn't spin.

If the fan spins at 24 volts, try a drop of oil on the fan bearing, that may help it run at 16 volts.

[drewl]

The fan works, it's just noisy as hell so customer wants it replaced.

And Dude, why wouldn't the fan work with 24v applied?
It does and should, it's a 24v fan.

[The Dude]

Well, you said it didn't work with 16V, so I mistakenly made the leap that the fan itself was shot. Apparently, I was wrong in my assumption.

[Jazz P Bass]

Although in the initial post it was never explicitly stated that the fan 'works' when connected to a 24Vdc supply.

[gui_tarzan]

I have a non-pro SVT III and I don't hear the fan unless I plug two cabinets into it to run it at 350w. With one 8 ohm cab it runs 200w and I don't think the fan has ever come on in that mode. It might be running very slowly, but I can't hear it if it is.

[drewl]

No problem.

Fan always worked, just loud as I mentioned.

The owner mentioned the fan circuit being a problem with these amps (?) which is why I asked about the operation of the fan.

[gui_tarzan]

Could be with the pro series, I don't know. I can't find much information on the 'net about my non-pro at all. There is very, very little available.

[soundguruman]

There is a huge variation in LM 35, and there is several different temperature ratings...
so they are not all the same.

The Chinese convention lets the amp get really, really hot, before the fan turns on....and I feel that this shortens the life of the components.

I would rather have the fan ON, when I turn the amp ON. At least, at a slow speed, and then increase the speed as the amp warms up.
And you can modify the circuit to do that.

But basically, I disagree with the Chinese design conventions. I think that it's very poorly thought out.
It's definitely not the best way to cool the components, to extend the life cycle.

[mozwell]

svt3 pro & non pro

[R.G.]

The Chinese convention lets the amp get really, really hot, before the fan turns on
...
But basically, I disagree with the Chinese design conventions. I think that it's very poorly thought out.

OK, let's do this again.

I have over a decade of experience working with Chinese factories. If *you* have direct experience with Chinese factories, let's hear about it.

Also, I'm very interested in these "Chinese design conventions". Design conventions as such were very difficult to enforce in the one design lab I worked in, let alone across a multi-location corporation or a very large nation. If you have any direct proof that there *are* "Chinese design conventions", let's see it.

Or, you could just admit you don't like Chinese produced stuff, but have no rational basis for this dislike. That is, it's an ethnic bias with no basis in fact.