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MTI SVT Fan Replacement

#21
Those are wires soldered onto the terminals that the fan plug would have plugged into.

the third wire is for bonding the back panel to safety ground.
 
#23
I am hearing that the air, shearing past the existing holes in the back panel, makes a fair bit of noise. I am also hearing that this fan was designed for more industrial purposes and is not terribly quiet, even without the shearing noise. Given this, I might fabricate a new back panel, with a cutout, then use a wire screen over the fan (sharply reducing wind shear noise). And then, if I install a quieter 115 VAC fan which moves, say, 50 CFM, then the amp would still have adequate ventilation and noise would be reduced to the best of my ability, right?
 
#24
I have some of these if they might work by chance....
20201014_143505.jpg
 
#25
I would start by just changing the fan and see before going down the road of a new grille.

Does the SVT even need a fan? Bill Hughes has said that the amp didn’t need a fan to receive regulatory approval (at least back in the day).

The 6550’s and cap cans can take the heat. Is it good to have a fan in this amp? Sure.

The SVT is a loud amp. On stage up to spec fan noise isn’t an issue. For quiet recording or home levels, the fan can be unplugged, a quiet external fan can be used to blow air into the back of the amp.


A7B8D48F-A5E4-43B4-818D-8A9A45AC2A17.jpeg





Old Fart said:
I am hearing that the air, shearing past the existing holes in the back panel, makes a fair bit of noise. I am also hearing that this fan was designed for more industrial purposes and is not terribly quiet, even without the shearing noise. Given this, I might fabricate a new back panel, with a cutout, then use a wire screen over the fan (sharply reducing wind shear noise). And then, if I install a quieter 115 VAC fan which moves, say, 50 CFM, then the amp would still have adequate ventilation and noise would be reduced to the best of my ability, right?
Click to expand...
 
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#26
So....one option is to KISS. Leave it alone. Put the fan on the backplate and reattach the backplate without plugging the fan in. If I gig with this, then perhaps I will turn sideways occasionally and and blow into the front panel. LOL
 
#27
Old Fart said:
Hm. I am forming the impression there may be little I can do here without significant modifications. FWIW, here is a picture of the 3-conductor plug. We think this is the twelfth MTI SVT made. It is more like a Magnavox-era SVT than a MTI. Except for the outward appearance.View attachment 4017861 View attachment 4017862
Click to expand...

You should be able to salvage the pins or buy new pins for the white Molex quick connect, so you are not limited in any way. I believe there is a special extraction tool you can buy, or just futz around with a dental tool or a jewelers screw driver and you should be able to get the pins out of the connector.

The fan I bought was plug an play for my amps because both existing fans already have this Orion connector on a pigtail. The pigtail is wired in to the same Molex you are showing.

upload_2020-8-19_16-54-27-jpeg-jpg-jpg-jpg.jpg


So the options you have are buy a fan with a hard wired pigtail and bare wire ends. Or buy a fan with a separate plug in receptacle.

FYI: The "TB" on the end of Orion fan part numbers stands for Terminal, Ball Bearing. I believe "terminal" refers to the receptacle for this plug. The pigtail with the plug is sold separate. This is because there are multiple options for the angle of the plug. If the part number ends in "WB," it stands for Wire Leads, Ball Bearing.

Since you are already running a 38mm fan, I believe the Orion P/N @agedhorse provided is the quietest. The 38mm EBM fan @beans-on-toast suggests is about 3dB louder, but pulls more air. Seems you have two great candidates and should try one of these before you go nuts fabricating a new back panel or modding your existing panel. Also do check to makes sure the fan is blowing the air out through the grating, as this should result in the lowest noise.
 
#28
Old Fart said:
So....one option is to KISS. Leave it alone. Put the fan on the backplate and reattach the backplate without plugging the fan in. If I gig with this, then perhaps I will turn sideways occasionally and and blow into the front panel. LOL
Click to expand...

:rolleyes:

Despite Mr Hughes brag on the amp not requiring a fan, let's keep in mind he did install one, and I would assume he did so for a good reason. IMHO try a quieter fan.
 
#29
BasturdBlaster said:
I have some of these if they might work by chance....View attachment 4018056
Click to expand...

Wrong size, that's an 80mm fan and will be much louder per cubic foot of air moved.

Wasnex said:
:rolleyes:

Despite Mr Hughes brag on the amp not requiring a fan, let's keep in mind he did install one, and I would assume he did so for a good reason. IMHO try a quieter fan.
Click to expand...
Correct, for long term reliability it's a very good idea. Just because it meets and older regulatory threshold without a fan doesn't mean that it's a good idea (and the regulations have changed somewhat which would make it more likely that it would need a fan today.
 
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#30
Just to be clear, I didn’t recommend not using a fan. It is common for people to disconnect the old noisy fan when recording.

Bill’s statement was “SVT's didn't need the fan, it will pass UL without one.” Well, at least at the time. Requirements are always changing. The V4B, another one of his amps, didn’t have a fan. That amp runs very hot. I wonder if his experience with the Stones may have prompted having one in the SVT, just to be safe. They really pushed those amps.

The maximum bulb temperature of the GE6550A was listed as 250 degrees C (482F). Of course the service life of other components has to be considered. Better to run the caps well under spec.

https://frank.pocnet.net/sheets/135/6/6550A.pdf
 
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#38
I received, and now installed, this fan which was suggested by Agedhorse. It is slightly less CFM, but only 25 db and has the exact same geometry as the outgoing fan. HUGE improvement. WAY quieter:

Invalid Link Removed

For those of you MTI owners looking for a quieter fan, this fills that bill. But......the fan I am removing is not the original fan, and I notice the fan fasteners do not match the holes in the screen. Additional holes in the screen, which I believe are visible in the pics I took, exist. They may have been created at the factory, or later. Just sayin'....check that out.
 
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#39
Old Fart said:
I received, and now installed, this fan which was suggested by Agedhorse. It is slightly less CFM, but only 25 db and has the exact same geometry as the outgoing fan. HUGE improvement. WAY quieter:

Invalid Link Removed

For those of you MTI owners looking for a quieter fan, this fills that bill. But......the fan I am removing is not the original fan, and I notice the fan fasteners do not match the holes in the screen. Additional holes in the screen, which I believe are visible in the pics I took, exist. They may have been created at the factory, or later. Just sayin'....check that out.
Click to expand...


If you mean the pic in post #1. That looks pretty typical to me. AFAIK the fans mounts do not typically match the cut out of the grating perfectly so a bit of filing is necessary. Did you need to cut new holes?
 
#40
No. The outgoing fan and the new one have exactly the same mounting fastener geometry. But since the outgoing fan is not original, I do not know whether the factory cut the new holes. Three of them it seems. My problem is solved, but I am just offering information for the next guy. Or lady, of course.
 
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