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Acquiring an SWR SM-900, reasonable?

#61
Dave Hill said:
I had a few of the early ones and they were all 800w bridged/mono into 4 ohms. This capability was one of the reasons why I went with SWR and not the Eden WT-800.
Bridged into 8 ohms min seems silly to me…
You’re pretty much limited to a single cab in bridge mode.
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No, the earliest version was bridgable into 8 ohms only. Because it was not the “best” choice, adjustments were made to the design and the later models were bridgable into 4 ohms.
 
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#62
agedhorse said:
No, the earliest version was bridgable into 8 ohms only. Because it was not the “best” choice, adjustments were made to the design and the later models were bridgable into 4 ohms.
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I'm not trying to contradict you in any ways. But all of the SM-900 I found for sell were 4 ohms minimum in bridge mode. Even the oldest ones. Also, the one I'm interested in seems to be among the latest models, not the one from the 90s.
That's where I'm missing something probably.
 
#63
I will have to look at my records to verify that I am not mis-remembering from a different model in the line. There is an array of mixing and matching of power transformers and power amp modules throughout the line.

There was also a version of the SM-900 with two power transformers. I recall that being a later version as well. I do not have all of the data either, some was lost many years ago.

The number of later models is not very large, and there are several earlier versions. I will look to see what I can find.
 
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#64
agedhorse said:
I will have to look at my records to verify that I am not mis-remembering from a different model in the line. There is an array of mixing and matching of power transformers and power amp modules throughout the line.

There was also a version of the SM-900 with two power transformers. I recall that being a later version as well. I do not have all of the data either, some was lost many years ago.

The number of later models is not very large, and there are several earlier versions. I will look to see what I can find.
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Thank you very much for your involvement.
Yes, there was a version of the amp with two power transformer. And I actually wonder if this very one is not one of them. I heard they are among the most reliable.

Maybe also look by yourself at all the SM-900 for sell currently, and I swear you won't find any with this 8 ohms minimum bridged. Unless I really have to buy a pair of glasses.
 
#66
Dave Hill said:
Unless they went back and forth, I’m quite sure all the older ones were 4 ohm min in bridge mode. I had three, including a very early one…(SWR Engineering) all 4-ohm. Still have a later, but, pre-Fender model. (SWR Sound)
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You confirm what I witnessed too.
Would you say it's a reliable amp? Does the last one you have has black and white logo or red and black logo?
 
#67
I used to own a 900 with the early "purple" graphics, with the date on the power transformer indicating 1996 build. It bridged into 4 ohms.

It was rock solid, drove it hard for years. Only sold it because it was way loud for the gigs I started getting. Hugely regretting that move.
 
#69
If the amp was built using the SWR-2000 power amp module, or earlier and has 4 output transistors per module, it should be rated for 8 ohm bridged only. There was a protective limited that prevented (or may prevent) damage driving into 4 ohms bridged, and maybe some versions considered this acceptable for 4 ohm bridged operation but the later versions using the SWR-500/1000 modules with 8 output transistors (same part) were designed specifically for 4 ohm bridged operation.

This is what my documentation suggests and the circuitry directly supports this premise. The 500/1000 module was designed by Fender (Corona, CA) and it's significantly more robust/advanced. The pre-Fender versions had significant issues with thermal shutdown and failure, the Fender version addressed this specifically, plus it's UL/IEC 60065 compliant.

Here is the earliest (I believe this was rated at 8 ohms bridged only) and there may have been a version with a single SpeakOn for bridged output too:
361111B.jpg


Here's another version (the issue here is that 4 ohms bridged requires 2 ohm minimum load on the dual outputs. In this example, the dual outputs are rated at 4 ohms minimum load. I believe Fender carried this version over during the transition (while figuring out how to revise for compliance) and because there was a large quantity of work in process and inventory:
0ef3345a-2d94-41d0-9c47-083cdbdb8c44.jpg


Here's the older versions with the SWR-2000 modules:
NJI9E7O-iiwB0hKT3u9Up8npV38XOXExtgmsTxeGY4zLtaABXUwiAN_4ssG0rxxr-fZGXLkKhuEyxRCU0JGi42LPvry1O0bm.jpg


Here's the latest Fender version (I think this was differentiated with the 3 dimensional SWR badge) with the new modules, dual fans and transformers, it is 2 ohm stable in dual mode and 4 ohm stable in bridge mode. It's much more robust:
fetch?id=872974&d=1510347544.jpg



Of course, folks are free to believe anything they want to, should they so choose.
 
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#76
baxter_x said:
Well, I asked him if it was a dual transformer/fan version. He told me I should consider another amp......
I guess this was my last attempt to convince myself I should buy this amp.

Thanks a lot to all those who took time to guide me and answer my questions.
Click to expand...
Disappointing for sure, but a good call in the bigger picture IMO.
 
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#77
I have a SM-400 that I have played for years. I tried three times (recently) to buy a SM-900. Two of them came damaged. Not packed well enough and the mounting ears and hence chassis all bent up. The last one came well packaged in a rack mount but one channel didn't work. One of them, incidentally, they didn't even want shipped back so I will give it to you for the price of shipping. Good for parts, at least. I'm planning to sell my entire SWR rig: sm-400, goliath 4X10 and big ben 18". At 71, I can't really carry that stuff around anymore and busy acquiring a lighter rig. I will say, though, I still and always loved the tone and power. My SM-400 over these cabs was plenty of power, even for outdoor gigs.
 
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