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Modifying SVT for 8 ohms-worth the effort?

poorbassist15

poorbassist15

Dec 29, 2009
1,372
148
Danville, VA
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#1
So, I should preface though I'm not a certified tech or anything I do know a little about tube amps, know reasonably how they work and of the dangers, both physical and monetary, that come with messing with gear.

So I have a Pignose B100V and I LOVE the sound of tubes, after making my jump from solid state about 2 months ago. I had been using borrowed SVTs for a while and tried pedals, effects, amps, anything I could to get that sound and now that I have actually bought a tube amp there really is no substitute.

My issue is, 100 watts ain't getting it done. It works for smaller stuff with a 410 but there are venues we play that require a little more and on rare, very rare, occasions I don't have PA support, there is absolutely no way I would be heard. I'm getting the volume I need but my amp is running out of headroom for strong notes below G. I'm using a 4003 that might occasionally be tuned down to C# but never lower.

I'm about to try running my Hartke 410 with the Pignose and slaving it to the power amp of a Peavey Valveking to run a Peavey 1516 and while this will probably get it done enough that I'm happy, it's a bit ridiculous. I know that I LOVE the sound of the SVT and that I'm really only trying to create a substitute for it.

The issue is, lack of 8 ohm taps on the output transformer. All of my cabs are 8 ohm except the PR410HLF I have but that would be suicide for a tube amp. It loves to eat amp power. I am really digging this new 1516 I just picked up but it's 8ohms. However, I've been thinking, someone has to have made an aftermarket output transformer for the SVT. Mercury Magnetics seems to have exactly what I'm looking for, a replacement output transformer for SVTs with 4, 8, and 16 ohm taps(part number ASVT-OM). Heyboer has one that doesn't list what the secondaries are, just that it has 2 of them and they are symmetrical.

Given that both of these are 400 freaking dollars, does anyone have anothersuggestion or even if it's worth the effort? I could get an SVT for 8 or 9 hundred bucks and have 400 more into it but I'd have exactly what I want, an SVT I can use anywhere. I know there's a bunch of y'all on here that know more than I do, so tell me how dumb I am.
 
#4
I can do both of the above, but transporting the full stack for smaller gigs is a bit nuts, and I really don't want to spend that much on an amp I can't use all the time. To get another 300 watt tube amp with an 8 ohm out for a reasonable amount of money only really leaves me with one option: the Fender Super Bassman. I've tried one and it sounded wonderful, but it's not exactly an SVT.
 
#7
I don't think there is too much of an issue running an SVT at 8 Ohms. That's not far enough off to cause the amp much worry even if you are pushing it. You will end up with a bit less than 300W from it though. If it was me, I would probably just do that. If you have an 8 Ohm, 4 driver cabinet (410, 412) you can rewire it (or even put a switch in) for 2 Ohms, then you can use the 2 Ohm tap on the SVT. I did this for a while with an old SWR Goliath III and it was fine.

That said, it wouldn't hurt to try it with the PR410HLF. It's not going to hurt the amp. I ran my SVT with an SVT410HLF for a while and had no issues with it in a loud band situation. It's only slightly more efficient than the PR.

I will say that I was never fully satisfied until I drove a sealed cabinet with the SVT. I love the Ampeg 810 but bought a Bergantino NV610 because it captures that 810 vibe in a much smaller and lighter package. I got rid of my 410HLF for it and the 610 is way easier to move than the HLF was.
 
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#8
Mark Reccord said:
I don't think there is too much of an issue running an SVT at 8 Ohms. That's not far enough off to cause the amp much worry even if you are pushing it. You will end up with a bit less than 300W from it though. If it was me, I would probably just do that. If you have an 8 Ohm, 4 driver cabinet (410, 412) you can rewire it (or even put a switch in) for 2 Ohms, then you can use the 2 Ohm tap on the SVT. I did this for a while with an old SWR Goliath III and it was fine.

That said, it wouldn't hurt to try it with the PR410HLF. It's not going to hurt the amp. I ran my SVT with an SVT410HLF for a while and had no issues with it in a loud band situation. It's only slightly more efficient than the PR.

I will say that I was never fully satisfied until I drove a sealed cabinet with the SVT. I love the Ampeg 810 but bought a Bergantino NV610 because it captures that 810 vibe in a much smaller and lighter package. I got rid of my 410HLF for it and the 610 is way easier to move than the HLF was.
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You will assuredly cook a power tube running the amp at 8 ohms. It won't happen immediately but it will happen. I used to run a 6ohm cabinet with my SVT.
 
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#9
DiabolusInMusic said:
You will assuredly cook a power tube running the amp at 8 ohms. It won't happen immediately but it will happen. I used to run a 6ohm cabinet with my SVT.
Click to expand...

I've cooked a scattered power tube in mine (and seen lots more) operating at 4 Ohms so that's not limited to running it with an impedance mismatch. That mismatch really doesn't tax the amp very much, it's not far enough off the nominal to worry about. Open circuit? Yeah, you're going to flash over the OT insulation or plate to cathode in a power tube but 8 Ohms? I wouldn't worry about it. And it's not just my opinion. Bill Hughes (one of the guys who designed the original SVT) has posted on TB that it's not an issue for that amp.
 
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#10
It would be better if you obtained a 4Ω cabinet that will handle the output of your SVT. Changing out a perfectly good OPT just so you can run an 8Ω cabinet is false economics.

I’ll add that on this amp, working at the voltages it does, it's not a simple wiring job. The feed back loop has to be correctly done otherwise you’ll have a 300W oscillator.
 
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#11
DiabolusInMusic said:
You will assuredly cook a power tube running the amp at 8 ohms. It won't happen immediately but it will happen. I used to run a 6ohm cabinet with my SVT.
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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.
 
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#12
poorbassist15 said:
The issue is, lack of 8 ohm taps on the output transformer. All of my cabs are 8 ohm except the PR410HLF I have but that would be suicide for a tube amp. It loves to eat amp power.
Click to expand...

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.
 
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#13
DiabolusInMusic said:
You will assuredly cook a power tube running the amp at 8 ohms. It won't happen immediately but it will happen. I used to run a 6ohm cabinet with my SVT.
Click to expand...


Yes I unknowingly ran one at 8 ohms for a while and while it didn't hurt the head, it had less power and went through tubes quickly, i knew there was something wrong when i went and jammed with a new band that was pretty loud and it just didn't have the oomph it needed.
 
#14
Mark Reccord said:
I've cooked a scattered power tube in mine (and seen lots more) operating at 4 Ohms so that's not limited to running it with an impedance mismatch. That mismatch really doesn't tax the amp very much, it's not far enough off the nominal to worry about. Open circuit? Yeah, you're going to flash over the OT insulation or plate to cathode in a power tube but 8 Ohms? I wouldn't worry about it. And it's not just my opinion. Bill Hughes (one of the guys who designed the original SVT) has posted on TB that it's not an issue for that amp.
Click to expand...

It won't hurt the amp but sounds like krap, lot less power and goes through tubes quickly, ask me how I know that?:roflmao:
 
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#15
OP: If you feel that the 4-ohm SVT-212AV cab suggested by beans in post #5 is "too much cab" for you, then an option you may wish to consider is having Don at Low Down Sound (LDS) make you a sealed cab that has only one 4-ohm speaker. I don't know which speaker Don would recommend for that, but I'm sure he would know!

Just a suggestion! :)

(And btw, welcome to the wonderful tone and feel of tube amps! I agree with your comment that there is no substitute!)
 
#16
Wait a second...Poorbassist, you were referring to the SVT 212av when you said it was "too much cab" when you're using a PR410hlf or a Hartke 410 already? It's the same size as your basic 410, considerably smaller than the PR410hlf, and weighs a good bit less. Use any less of a cab than one of them and there's not even a point in using a 300w amp in your situation.
 
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#17
JimmyM said:
Wait a second...Poorbassist, you were referring to the SVT 212av when you said it was "too much cab" when you're using a PR410hlf or a Hartke 410 already? It's the same size as your basic 410, considerably smaller than the PF410hlf, and weighs a good bit less. Use any less of a cab than one of them and there's not even a point in using a 300w amp in your situation.
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The PR410HLF is a real PITA to move, I'd rather lug my 810 cabs than that one. It weighs as much as my 810 if not more and is very awkward to move, it sounds great though. It's probably double the weight of a SVT 212av.
 
#20
JimmyM said:
Wait a second...Poorbassist, you were referring to the SVT 212av when you said it was "too much cab" when you're using a PR410hlf or a Hartke 410 already? It's the same size as your basic 410, considerably smaller than the PR410hlf, and weighs a good bit less. Use any less of a cab than one of them and there's not even a point in using a 300w amp in your situation.
Click to expand...

I was going to say the same thing but you already did.

OP--get the 212. It's a great sounding, easy moving, one-cab solution to using an SVT all the time. It's become my most used cab for this reason, allows me to take an SVT to any gig I want and is obviously easier to drop an SVT on than hoisting one up on an 810 (not that I'm opposed to hoisting one up on an 810 ;)).

11800142_866729953401977_2691324328491113050_n.jpg
 
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