Help me restore the jack on my early 70's squareback SVT 810

blockinlay · #1 12-23-2011, 02:40 PM

Need help with my early 70's 810 SVT cab. Jack issues.

I have never been happy with my jack on the back of my 810 cab. It's a Switchcraft 3-Conductor Female XLR.
It looks original, but I don't know if it is. Aren't these cabs supposed to have a 4-conductor jack?
The jack is missing the clip to unlock the matching cable, so I want to replace it with the appropriate correct receptical, which I believe should be a 4 pin. I can't find any info on wiring, or jack hook up for this cab. It has original speakers, and there are only two wires going to the jack that's there. It does work as it is though.
I read that there is a reason for the four pin cable, and that it protects the amp.

Can anyone give me some good information on restoring my cab?

BTW, I just got my 73 head back from service. A few microphonic preamp tubes and 2 questionable power tubes replaced, as well as a couple resistors, power cord, and new feet.
Jim Walton is the amp tech. He's in Philadelphia. Great guy. Really knows vintage tube amps, and came highly recommended for working on my SVT. Taught me a bit about my head before I left too. Interesting. I didn't know it was only 200watt at 4ohm with one cab, and 300 at 2ohm with two. He said these amps were made to be all purpose amps, not just bass amps, and showed me that the midrange is active. Really colors the sound when you dial it. He said the switch above the midrange will blow speakers if not careful, and he demonstrated the amp when I picked it up.

I also hooked up with a speaker repair guy this week. Miller Sound. World famous. His family's been in the business since the 30's. Lives right down the road. Says he's got cones to recone my vintage speakers if I ever need to. I told him I thought one was buzzing. He fixed a torn cone on a Celestion guitar speaker for me when I dropped off a couple shot vintage Sunn 15's for a friend of mine.

coreyfyfe · #2 12-23-2011, 02:49 PM

One the four pin jacks pins 1 and 4 went to the speakers, pins 2 and 3 were connected to each other to complete the standby circuit. If your head doesn't have the attached 4 pin connector using that jack is useless. I'd just change it to a standard 1/4" connector or a speakon if it's already a big enough hole.

blockinlay · #3 12-23-2011, 02:57 PM

The head has 1/4" jacks. I could just change the cab to a simple 1/4 jack then, right?

will33 · #4 12-23-2011, 03:24 PM

Quote:

Originally Posted by blockinlay

The head has 1/4" jacks. I could just change the cab to a simple 1/4 jack then, right?

Yes, simple tip +, sleeve - to the speakers. 2 wires, that's it.

Tim1 · #5 12-23-2011, 03:30 PM

"200watt at 4ohm with one cab, and 300 at 2ohm with two".....news to me for a 73 SVT?? News to me, but I don't claim to be an expert. Anyone else know anything about this?

will33 · #6 12-23-2011, 04:10 PM

Quote:

Originally Posted by Tim1

"200watt at 4ohm with one cab, and 300 at 2ohm with two".....news to me for a 73 SVT?? News to me, but I don't claim to be an expert. Anyone else know anything about this?

Yeah, it's bogus. SVT or any other tube will have maybe not exact but very similair output from all the taps. Some of the overall tone may change character slightly but output will be pretty close, assuming it's in good working order, biased properly, etc.

blockinlay · #7 12-23-2011, 06:18 PM

Well, the tech told me my head was in very good condition, and that it was putting out 200 watts at 4ohms. I'm guessing that was before clipping. When I said it was a 300 watt amp, he said it would put out more with a second speaker attached and running at 2ohms. I know he is very knowledgeable and uses the proper testing equipment. Perhaps the amp would put out more with a full set of new 6550's. He only replaced two that made pop noises when tapped, and he matched them to be close to the 20 year old chinese tubes that were there and still good. I said I wanted the amp back in dependable working order, not restored to 100%. Even if only running 200 watts at 4ohms, this head has way more power than I'll ever need.

JimmyM · #8 12-24-2011, 02:15 AM

A working SVT should do 300w at 4 ohms or at least close to it. If he tested the tubes and they were good still and he was able to match the new ones with them, I think something is up with his testing equipment.

popgadget · #9 12-24-2011, 04:08 AM

Quote:

Originally Posted by blockinlay

I also hooked up with a speaker repair guy this week. Miller Sound. World famous. His family's been in the business since the 30's. Lives right down the road. Says he's got cones to recone my vintage speakers if I ever need to. I told him I thought one was buzzing. He fixed a torn cone on a Celestion guitar speaker for me when I dropped off a couple shot vintage Sunn 15's for a friend of mine.

In Lansdale, works out of his house? He reconed some EV12's for me and did a great job. I'm only 15 minutes from him, we must be neighbors....

coreyfyfe · #10 12-24-2011, 05:59 AM

Amped definitely rated them as 300 watts at either 2 or 4 ohms, as said above that's just how amps with output transformers work. Amped also recommended two cabs because the original square back cabs were only rated for 240 watts each. They certainly seem to take a pounding and not complain though. I've been driving mine pretty hard lately and it hasn't been complaining.

blockinlay · #11 12-24-2011, 10:16 AM

Quote:

Originally Posted by popgadget

In Lansdale, works out of his house? He reconed some EV12's for me and did a great job. I'm only 15 minutes from him, we must be neighbors....

Hey, what's up neighbor? Yeah, Lansdale. Nobody knows Lansdale. I write Phila, and people know that.

For my cab, I just bought a replacement receptical identical to what was in the cab.

As far as the amp is concerned, I believe the tech just swapped in two new power tubes to put the amp back in working order and so it would hold bias. He also changed out three preamp tubes he thought were causing microphonic noise. I don't know if any tubes were tested. After changing out an open screen grid resistor and another resistor in the preamp, he found that two of the power tubes made pop noises when tapped on. He didn't like that, and in all likelyhood, that's what caused the one resistor to fail, so he swapped them for similar tubes. One is a Mesa, and one a GT, both are Chinese and look identical to the other four tubes. I don't know how he tested it, because I wasn't there, but when I dropped the amp off, he showed me quite a bit of electronic testing equipment and described how he goes through an amp. It was over my head. I'd wished I videoed it on my Iphone. The amp is working fine. I was just playing through it. If I crank it up, things will fall off the shelves in the next room. As far as wattage, all I know is what he told me. Perhaps I'll discuss it further with him.