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200 Watt SVT? How to do it?

#121
big90sbasshorns said:
That being said, I would now like to throw the suggestion of an isolation box for your cab into the ring. If you can find the rig specs for a lot of major touring acts just about everything on stage is just for show, the real rig is screaming with the volume at "10" under stage in the tech area in an internally mic'd iso. box.
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I've actually had the idea for a while to take a single 6" or single 10" speaker, mount it in a FULLY CLOSED box with an RE20 pointed at it. Put a big brass handle on top and all the stupid necessary jacks it would need.

Then push the heck out of if with whatever I want. A fuzz pedal that produces speaker-cone distortion.

OR, instead of these cute little fuzz pedals made with one 12AX7, build a fuzz pedal with one 6550.

(But Jimmy's right... part of the appeal is the pant-flapping, sternum-vibrating effect the 15"s produce on stage.)
 
#123
I've never tried it before, so I don't know what would happen or if this even makes sense to try - what about using only 1 cab to mic (provided you do mic at gigs) and actually push volume on stage and setting the remaining ones on their "face" so they fire right into the stage giving you the physical sensation of bass without the punishing volumes?
 
#124
big90sbasshorns said:
I saw your pic with the full 4 cabs, is that your gigging rig - or do you scale back when you gig if you're not playing a HUGE room?
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Usually just two 15"s, or two 18"s if I'm in the mood. I've never gigged those two particular 18"s since they're kind of bulky. I used to have some more compact 18"s (EVs) that were easier to lug around and sounded great, but I sold them when I had to move. I'm planning to sell these particular 18"s and get another more-compact pair, or just build some TL505s to keep the EV vibe going.
 
#125
MAMMOTHvolume said:
also @ paul, not sure i'd want to run el34's at that kinda voltage without properly regulated screens. They can take it but i think you'll burn through them far to quickly
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With todays high voltage MOSFETs regulating the screens would be fairly simple. Limiting the screen current can be accomplished by increasing the "standard" 1KΩ 5W screen resistors to 2K2Ω 5W. I didn't say it would be easy! :)

Paul
 
#127
BassmanPaul said:
Back in the day when 100W amps were all we had, I'd add a slave and a second cabinet. Taking a V4 and cloning the power amp section would be fairly easy and comparatively inexpensive.
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Yeah, we tossed this idea around earlier in the thread. One V4B preamp with two V4B output stages, built into one headcase.

V4Bs are cheap enough nowadays to try it, but the weight would absolutely kill you if you kept all 4 transformers.

But I'm willing to entertain it... practicality is not my goal. Simplicity is.
 
#129
ampegfuzz said:
Ok doin a little messin around now with the amp but what bass should i use since i have no RD? My ric with neck solo, tone off, and rounds or jazz neck pickup, tone off, with flats?
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Thanks ampegfuzz.

Either should work. To be honest, the bass you use is irrelevant. The RD pickups are nothing special. Once the amp is turned up that high, and you roll the tone all the way off on the neck pickcup, it's fuzz city no matter what bass you use. The only difference would be how much sustain each bass has.
 
#130
I guess I'm still thinking in terms of 'other ways' to approach this, and I'm stuck thinking on the cab... It sure seems like you could push the hell out of a single 15 and get the tone you're after... if the only goal is to alleviate "soundguy frustration" it seems like you just need to get the tone you currently have, with less volume. The instant solution to me seems to be use less speakers, as long as they can individually handle that amount of power. Depending on your drivers those TL606's should be fine with SVT power, right?

Or another way -- and maybe this wouldn't work with a tube amp, as I'm a SS / hybrid guy myself -- couldn't you run two 8 ohm cabs in series to get a 16ohm load to reduce power and volume that way? I have a feeling there's a reason why you couldn't, but it popped into my head, so why not.
 
#133
ishouldbeking said:
Generally speaking you could safely do this with a SS head though, right?
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a SS head without an output transformer. I know the Jonas Hellborg amp is a SS power amp with an OT, but I don't know of any others that use that kind of setup.

fu22ba55 - I have a quick and dirty sample of my fuzz through my B-15 (couldn't do the SVT - my neighbors are home). Send me a PM and I'll email you the file.
 
#134
ishouldbeking said:
Or another way -- and maybe this wouldn't work with a tube amp, as I'm a SS / hybrid guy myself -- couldn't you run two 8 ohm cabs in series to get a 16ohm load to reduce power and volume that way? I have a feeling there's a reason why you couldn't, but it popped into my head, so why not.
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on an SS amp, yes you'd have less power, but it wouldn't work because you don't ever want to hear a SS amp's power amp clipping. :eek:
 
#138
johnk_10 said:
i'm recommending lowering the plate voltage on the output tubes, not the preamp.
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That's what I was thinking in adding a half wave rectifier in addition to the existing rectifiers, dropping the plate/screen voltages to the output stage only and maintaining the same voltages on the preamp stages. That could be switched to yield 2/3 or full power I suppose. I was thinking not to make more heat in the chassis by adding dropping resistors. That's more of a caveman approach to the problem.

OTOH, look at the dual/triple rectifier guitar amps. This is basically what they do, with the addition of a tube rectifier option and/or half wave/full wave rectifier.

Now if you really wanted to dirty the SVT up at 200W, you could use a 5U4GB parallelled for half wave to power the output tubes...:D

What you can do in the power supply is somewhat limited if you choose not to replace the (expensive) power transformer.
 
#139
DavidLopezJr said:
Well the big thing now a days for guitar amps to get that power amp grit at any volume level is the London Power Scaling system. I would contacting them and seeing if they could possibly do something for something with that many watts. It's something I've always wanted to do with an SVT.

http://www.londonpower.com/pscaling.htm
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I emailed London Power:

Have you designed a Power Scaling circuit able to withstand the output of a typical '70's or 80's Ampeg SVT? (300 Watts @ 4 Ohms)
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That would be the SF-1, which is rated for up to 900V. The screen voltage on this amp requires a simple mod to the SF-1, described in the kit notes. The current catalog description and photo shows the old version of the kit.

I'm interested in safely cutting an SVT's power down to about 220 watts (that seems to be the sweet spot).
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You can do that by pulling two tubes symmetrically: one from each group of three counting from each end.

Is this something I could have a London-Power-licensed-tech install on an SVT?
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Yes. You should also change the screen resistors from the 22R-500mW shunted by a diode to a plain 1k-5W with no diode. This will keep the amp from eating tubes and also gives the "loud" tone at low levels.
 

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