Modifying SVT for 8 ohms-worth the effort?

[bassmeknik]

I used my JBL K-151 (8 ohms) in a custom made cab with my SVT for 30 years without incident. Finally got an 810 then had to sell the SVT to pay bills. :/

 

[Korladis]

You will assuredly cook one no matter what you do. It is not official company policy, but Bill Hughes, one of the inventors of the SVT, has said on here that SVT's are so overbuilt that they can easily withstand a 2:1 impedance mismatch, even if you crank them hard. Obviously if you crank it hard, you'll burn out tubes quicker, but that's to be expected when you crank it hard.

Indeed. Power tubes wear out eventually, faster the harder you're pushing the amp.

Using an 8 ohm cab I assume would wear out the power tubes faster, but presumably the OP is using just one 8 ohm cab for smaller gigs when he's not going to be turning up that much.


That said, getting a V-4B would also be an option for said smaller gigs.

 

[Mark Reccord]

I haven't read anything else yet but I have a PR410HLF and it sounds great with an SVT head, in fact i think it is just as loud as my 810's. I don't know why they have a rep for being power hungry, I get a lot of volume out of it if I need it and have never pushed my head with it.

I did suggest that he should just use his PR410HLF with the SVT in my first post.

It won't hurt the amp but sounds like krap, lot less power and goes through tubes quickly, ask me how I know that?

I do think an SVT does sound a bit off when running at 8 Ohms. Kind of constricted sounding to my ears. I have done it with mine a bunch of times and always found it a bit lacking sound-wise. I don't think it affects tube life much though.

Indeed. Power tubes wear out eventually, faster the harder you're pushing the amp.

Using an 8 ohm cab I assume would wear out the power tubes faster, but presumably the OP is using just one 8 ohm cab for smaller gigs when he's not going to be turning up that much.


That said, getting a V-4B would also be an option for said smaller gigs.

If you're running an 8 Ohm load where 4 Ohms is expected, the tubes actually have to supply less current to the load than they would at the same (voltage) level and would run cooler than they would at 4 Ohms. The load impedance has no effect on the DC parameters (bias current etc.) only the AC ones. Peak AC voltages will be higher but if those are within the limits of the tubes/OT, I don't think it's much of an issue.

What I'm saying is that the danger in an impedance mismatch towards open circuit is not heat it's exceeding the voltage withstanding ability of the insulation in the OT or the plate-cathode of the power tubes (flashover). This is usually catastrophic when it happens and you really need to get into a gross mismatch before it becomes a problem in any sensibly designed amp.

 

[JimmyM]

I do think an SVT does sound a bit off when running at 8 Ohms. Kind of constricted sounding to my ears. I have done it with mine a bunch of times and always found it a bit lacking sound-wise. I don't think it affects tube life much though.

I agree with this, but it's still pretty darn good...just not as good as it could be running it at spec.