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Using a dummy plug on an early 70s blue line Ampeg SVT

#42
Is all this information the same for the SVT-VR?
Click to expand...

In terms of impedance switching, the SVT-VR is not designed the same way was the vintage SVT. The dummy plug can not be used with the VR to do what you can with the vintage amp.

The VR has a 2 / 4 Ω impedance switch on the back of the amp. There are two jacks wired in parallel and a single speakon connector. If you connect two 4Ω speaker cabs to the jacks, you set the switch to 2Ω. If you connect two 8 Ω cabs, you set the switch to 4Ω. If you connect a single 4Ω cab, set the switch to 4Ω.

The vintage design did the switching automatically when you plugged in. The VR achieves the same end but does it differently. It's maybe a bit more versatile since it allows you to plug in two 8Ω cabs and keep the impedance matched when the impedance switch is set to 4Ω.
 
#43
Yes, Bill. One thing that makes me very typical (and I pride myself on being a weirdo) is my undying love for "that tone."

My first SVT was in the 80s. It was a limited production made of all first gen NOS. I think it was made to reboost popularity. It had a plaque on the back that said "127 of 500."

After being bullied by bandmates unwilling to help move it, I sold it and regretted it for over a decade. The two years ago I found the HOLY GRAIL! A blue line sitting in a little repair shop on consignment (literally the ONLY thing for sale at all there, he was selling for a friend). Bad back and all, I still can't part with it and use it as much as humanly possible.

Thank you for your involvement in making the SVT! To this day I have never played a bad one. I had a 2 PRO for a while too and miss it as well. Different animal altogether … but somehow the same. MUCH cleaner and modern sounding but sooo good.
 
#44
whitespikebass said:
My first SVT was in the 80s. It was a limited production made of all first gen NOS. I think it was made to reboost popularity. It had a plaque on the back that said "127 of 500."
Click to expand...

Those were the Skunkworks series, the first run of SVTs made by SLM after buying Ampeg from MTI. They used the same circuit design as the originals (although with 12AX7s instead of 12DW7s as MTI did) with as much original stock as they had on hand (hence the limited number). After that the SVT was retired for a few years in favor of the SVT-II until the SVT-CL was issued.
 
#45
Just curious, what do you think if te skunkworks amps? It's been so long since I've had it.
I remember loving it, but not like I love my blue line.
But I also knew less about tone, playing in general, and I had a different cab. Between time and different cabs I can't really give it a fair comparison.
 
#46
Never played one in person, I've had a modern CL and my current 74 blackline. Between those two I prefer the 74, but similarly I know much more about the amps, playing, tone, etc, now, and use different cabs.

As Jimmy likes to say though, a properly working SVT sounds good like an SVT. Little things are different here and there, but that's what the eq is for.
 
#47
beans-on-toast said:
In terms of impedance switching, the SVT-VR is not designed the same way was the vintage SVT. The dummy plug can not be used with the VR to do what you can with the vintage amp.

The VR has a 2 / 4 Ω impedance switch on the back of the amp. There are two jacks wired in parallel and a single speakon connector. If you connect two 4Ω speaker cabs to the jacks, you set the switch to 2Ω. If you connect two 8 Ω cabs, you set the switch to 4Ω. If you connect a single 4Ω cab, set the switch to 4Ω.

The vintage design did the switching automatically when you plugged in. The VR achieves the same end but does it differently. It's maybe a bit more versatile since it allows you to plug in two 8Ω cabs and keep the impedance matched when the impedance switch is set to 4Ω.
Click to expand...


Thank you. I appreciate the info.
 
#53
If you are using a dummy plug, I figure that it's safer to plug it into the ext speaker jack.

The dummy plug acts to switch the speaker out jack to the 2 Ω tap on the output transformer. The speaker out jack has a shorting shunt. When nothing is plugged in, the jack is shorted from tip to ring.

If you have the dummy plug in the ext speaker jack and if the amp is mistakenly turned on without a speaker cab attached, the speaker output will be shorted. This will help protect the amp in the short term.

If the dummy plug is in the speaker out jack, a speaker cab is not plugged into the ext speaker jack, and the amp is turned on, the speaker out sees an open circuit. For a tube amp, this is worse than a short across the output.

So plug the shorting plug into the ext speaker jack.

The original SVT had a loop back safety circuit in the four conductor speaker cable. If the amp was turned on without the speaker cable connected to a cabinet, the amp was disabled and it couldn't turn on. A similar idea, employing a different circuit, was used in the B-15. When they removed the speaker cable and substituted a ¼" jack (in 1972?) they need to do something else so they went with a jack with a shorting shunt.
 
#54
Bill Hughes said:
The V4, VT22 V4B were all mine. They were a family of products.
Click to expand...
Excellent! Then maybe you can settle a discrepancy that seems to have cropped up recently on here with the release of the new redesigned V4B (BTW, I think you would really like it...Dawn Pfund IMHO did a terrific job recreating your original magic for today's world).

I was always under the impression that the V4/VT22 and V4B had different centers for the midrange control, with the V4/VT22 having 300, 1k and 3k centers and the V4B having 300, 800 and 2.5k centers. But recently, someone floated the idea which was backed up on http://www.ampegv4.com that they all had the same tonal centers of 300, 1k and 3k. But checking a scan of the original manual on http://www.ampegv4.com/images/Ampeg_Manual_P2.jpg, it appears that the mid switch's tonal centers were, indeed, different for the V4B.

Which is right? Thanks in advance for your willingness to share info to all us Ampeg nuts.
 

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