1969 Ampeg SVT Restoration Thread

[Chris 'Wighat' Jordan]

So many decisions to make. In any restoration, it comes down to how much you want to put into it. You can make it exactly as it was, improve on it, do just enough to make it work. At some point, you realize that you have more in it than you can ever get out of it if you sold the amp. At that point you are doing it for the technical challenges, because you are learning a lot, and for the love of doing this sort of work. There is so much involved. It runs from woodwork, cabinetry, upholstery, and metal work. The electronics is a whole other subject full of challenges and there's a lot to learn.

There is some information on the 4-pin connectors, cable, and Heyco bushings in the TalkBass Portaflex Wiki here: Technical - Amplifier - TalkBass Wiki

For the for-pin connectors I recommend that you use Switchcraft A4F and C4M connectors. For the 18 gauge four conductor cable, I use Belden 8454. In the past I've bought this cable from Surplus Sales of Nebraska but they are currently out of it. Other places sell it.

The bushings used to attach the cables were often made by Heyco. Details are in the Wiki. I find that on some amps, the holes have been enlarged and a different sized bushing is needed. Heyco (Strain Relief Bushings | Power Cord Strain) is still in business producing many of the same parts. The size of the bushing is based both on the cable diameter and the chassis hole size. Check out their web site. Samples are available from them and you can request different sizes so you can figure out what you need. Not sure about finding the square molding that was on the chassis power cord. My '71 had the same round bushing listed in the Wiki.

The Portaflex Wiki also details how to make adapter cables: Tips & Tricks (including modifications) - TalkBass Wiki.

For the power cord, I use Carol brand made by General Cable, 3/18 rubber jacketed cable (see attached, 01311). It is the same size as the original so works with the original bushing and chassis hole. I used to buy it at Home Depot but it seems that it is no longer available everywhere. Other places still sell it though, Walmart lists it (CAROL 01311 Service Cord, SJOOW, Black, 18/3, 50 ft. - Walmart.com For the plug, I buy a heavy black Leviton plastic plug from HD. This one: Leviton 15 Amp 125-Volt Rubber Grounding Plug-R60-515PR-000 - The Home Depot.

So many decisions to make. In any restoration, it comes down to how much you want to put into it. You can make it exactly as it was, improve on it, do just enough to make it work. At some point, you realize that you have more in it than you can ever get out of it if you sold the amp. At that point you are doing it for the technical challenges, because you are learning a lot, and for the love of doing this sort of work. There is so much involved. It runs from woodwork, cabinetry, upholstery, and metal work. The electronics is a whole other subject full of challenges and there's a lot to learn.

There is some information on the 4-pin connectors, cable, and Heyco bushings in the TalkBass Portaflex Wiki here: Technical - Amplifier - TalkBass Wiki

For the for-pin connectors I recommend that you use Switchcraft A4F and C4M connectors. For the 18 gauge four conductor cable, I use Belden 8454. In the past I've bought this cable from Surplus Sales of Nebraska but they are currently out of it. Other places sell it.

The bushings used to attach the cables were often made by Heyco. Details are in the Wiki. I find that on some amps, the holes have been enlarged and a different sized bushing is needed. Heyco (Strain Relief Bushings | Power Cord Strain) is still in business producing many of the same parts. The size of the bushing is based both on the cable diameter and the chassis hole size. Check out their web site. Samples are available from them and you can request different sizes so you can figure out what you need. Not sure about finding the square molding that was on the chassis power cord. My '71 had the same round bushing listed in the Wiki.

The Portaflex Wiki also details how to make adapter cables: Tips & Tricks (including modifications) - TalkBass Wiki.

For the power cord, I use Carol brand made by General Cable, 3/18 rubber jacketed cable (see attached, 01311). It is the same size as the original so works with the original bushing and chassis hole. I used to buy it at Home Depot but it seems that it is no longer available everywhere. Other places still sell it though, Walmart lists it (CAROL 01311 Service Cord, SJOOW, Black, 18/3, 50 ft. - Walmart.com For the plug, I buy a heavy black Leviton plastic plug from HD. This one: Leviton 15 Amp 125-Volt Rubber Grounding Plug-R60-515PR-000 - The Home Depot.

Wow, so thorough as always, thank you. I looked at the Heyco site and they do make strain reliefs for round cable that fit in a rectangular hole. I have to figure out what the original rectangular hole size was.

The fan on my amp is supplied by a short piece of lamp cord that has an octal plug on it that goes into the relay socket. This doesn't strike me as original. If not, how was the fan hooked up originally?

 

[beans-on-toast]

The problem with the power connector, is that I've seen all sorts of adaptations. The power cord was removable, there was a plug and socket. The end of the cord had a molded rectangular end. TV sets used to have these sort of connectors. They weren't very good and people changed them out. They used adapter plates so that they could use a round or rectangular Heyco, The adapter plate used the two chassis mounting holes that the original male connector used.

I think that you would be better using a round Heyco like the later SVT amps had rather than replicating the original which wasn't the best. See the images below showing the connector.

The cables connections to the preamp was a 12 connector rectangular Molex. They are a standard part, available today. Two wires came off the Molex and went to a two pin Molex. The pin sizes were the same, 0.093") on both connectors. The molex connector snaps onto the chassis. The male and female are held in place by friction. A bundle of wires covered in a plastic tube (often it was a clear sheath) went from the 12 pin molex to the preamp. A shielded wire carrying the audio signal was in there. You want to position the shielded cable away from wires carrying AC as much as possible to keep noise down. To do this, some people run the shielded wire outside the of the plastic sheath.


TV type power connector. These are still available but they aren't very good to use.

Power cord plugged in. Note the original two conductor molded plug on the end of the power cord.

See below, this is timv's amp. It looks like an adapter plate is used but there isn't one. The plate is often mounted from the inside using rivets or screws, a round Heyco is used.

Original speaker cable and four-pin plug with Heyco bushing.

12 pin chassis Molex connector showing offshoot two pin fan connector and cable running to the preamp. In this case, the shielded wire is outside the bundle going to the preamp.

Two pin molex plug on the fan end.

This is one kit that I found. The parts are readily available from mouser and other suppliers. You have to order the male and female housings as well as the pins separately. The little chassis mount wings are clipped off when the fan connector is installed inline. The advantage of using a fan connector is that the back panel and fan can be removed and won't get in the way when changing tubes.

 

[timv]

The pic with the power cord is my amp. I actually didn't use an adapter plate, the heyco bushing fit tight in the narrower part of the rectangle cutout so I left it like that.

I installed a circuit breaker in place of the fuse but mean to reinstall a correct fuse holder next time I have it open.

 

[beans-on-toast]

The pic with the power cord is my amp. I actually didn't use an adapter plate, the heyco bushing fit tight in the narrower part of the rectangle cutout so I left it like that.

I installed a circuit breaker in place of the fuse but mean to reinstall a correct fuse holder next time I have it open.

Neat! Thanks timv, I'll correct my post above. So often temporary adaptations are made but they work out and become permanent. I assumed that a plate was used because it is dark behind the bushing.

Here is another one with an adapter plate shown from the inside of the chassis. This is johnk's amp if I recall correctly. It provides a good view of the circuit board.

 

[beans-on-toast]

Looking through my files, I found a tube chart label that was done for an early SVT. I use art drawing paper in a laser printer, scale it to size, soak it in tea to age it, rough it up. The file that generates the label is a keynote file that runs on a mac. The repros are not exact but pretty close. I can't seem to post it here. I've attached a V4B cabinet label as another example, it looks a little more yellow in person.



An original.

Repro tube chart.

 

[Chris 'Wighat' Jordan]

Looking through my files, I found a tube chart label that was done for an early SVT. I use art drawing paper in a laser printer, scale it to size, soak it in tea to age it, rough it up. The file that generates the label is a keynote file that runs on a mac. The repros are not exact but pretty close. I can't seem to post it here. I've attached a V4B cabinet label as another example, it looks a little more yellow in person.



An original.
View attachment 708167


Repro tube chart.

View attachment 708168 View attachment 708169

Incredibly helpful information, thank you again. My head box has the original tube chart. There is a manila envelope pasted inside the head box that I assume is original. I assume it held the schematic. It is empty now so I am looking to acquire or reproduce one.

 

[beans-on-toast]

Yes, the envelope was included. It was glued onto the side near the tube chart.

 

[beans-on-toast]

One of the hardest things to find are those clutch head screws: Tips & Tricks (including modifications) - TalkBass Wiki

The amp used both machine thread and wood screw clutch heads.

 

[Chris 'Wighat' Jordan]

Yes, the envelope was included. It was glued onto the side near the tube chart.

What was held in the envelope?

 

[timv]

The schematics.

 

[Chris 'Wighat' Jordan]

I'm still suspicious that some of the earliest amps may not have come with the labeled back plate. It seems quite odd that anyone would discard theirs and I've only seen missing on the amps with the unpainted chassis and the relay tube socket. To further add to my suspicion, the perforated rear grill on mine does not look like it would jive with the back plate. The little sections that hang down over the back plate/jack area would not allow the labeled back plate to fit correctly. How do the perforated grill and and labeled back plate fit together on later amps?

 

[JimmyM]

I would so like to believe that you're right Mine didn't have a back plate, either. I bought a replacement from Bruce. But I really can't see it...they'd have to write on there with magic marker what everything does, and that's less than pro, even by 1969 standards.

 

[Chris 'Wighat' Jordan]

I would so like to believe that you're right Mine didn't have a back plate, either. I bought a replacement from Bruce. But I really can't see it...they'd have to write on there with magic marker what everything does, and that's less than pro, even by 1969 standards.

So, Jimmy, how does the back plate work on yours? Seems like it wouldn't lay flat if it went OVER the grill....see what I mean about mine? Or is the repro backplate heavy duty enough that it can support itself and just float off the chassis the thickness of the grill?

 

[coreyfyfe]

Check out Spencer's amp here. Might be a repro back plate since it's so clean but it's an early model with the tube relay socket.

Post Your 70's Ampeg SVT | Page 5 | TalkBass.com

Here's another I found on google image search, lists as a 1969, has the "pat pend" back plate

 

[beans-on-toast]

Have you decided what you are going to use to recover the cabinet? I use black marshall levant from tubes and more. It's a lot of work to strip, prep the wood and recover.

 

[Chris 'Wighat' Jordan]

Check out Spencer's amp here. Might be a repro back plate since it's so clean but it's an early model with the tube relay socket.

Post Your 70's Ampeg SVT | Page 5 | TalkBass.com

Here's another I found on google image search, lists as a 1969, has the "pat pend" back plate

I spoke with Spencer. His amp is a 69 and that is a repro plate from Fliptops. Like most all "69" SVT's, I don't believe that second one is a 69. One more little hint that the earliest ones may not have had back plates, the Fliptops repro - which is supposed to be exact for early SVT - does not appear to be a perfect match for my various jack holes, etc. Did yours line up perfectly, @JimmyM ?

Have you decided what you are going to use to recover the cabinet? I use black marshall levant from tubes and more. It's a lot of work to strip, prep the wood and recover.

Oh, yes, I'm all-in now! I have not been fretting over the head box because that is familiar territory to me whereas the electronics aspect is not. But, yeah, new corners, handles, grill cloth, shock absorbers and Tolex.

I heard back from my sheet metal savant today. He's on board to patch the ugly mod holes in the back of the chassis! This a relief because this guy is GOOOOOD.

 

[Chris 'Wighat' Jordan]

Well this showed up on eBay. It looks like a legit 69. It has the unpainted chassis, relay tube socket....but lookee there: a back plate. Obviously a factory back plate as it has the regulatory sticker and serial number tag. You can't see in the picture whether the grill has the lower tabs, but I'm thinking it does. All the screws have been removed from the backplate. So this tells me the grill goes under the backplate; note the three screw holes at each end and the four across the top.

 

[beans-on-toast]

The orange stickers that I've seen state City of Los Angeles, Approved for Electrical Safety, Department of Building and Safety. Electrical appliances had to have safety approval.

I don't know how it happens but a number of SVT's have the back plate missing. Some also don't have the back screen.

 

[JimmyM]

Yes, my repro back plate fits...well, it would if my tech hadn't replaced the courtesy AC plug with a detachable AC jack. As for laying flat, it doesn't but I don't think any of them do.

 

[Chris 'Wighat' Jordan]

I disassembled the pre amp this evening. Wow, what a difference from the power amp. I don't think anyone has ever been in there. Very tidy, clean and factory-like. Pardon all the pictures but I'm trying to be thorough in documenting this project.

Edit: forgot to add that the pot codes throughout the amp are split between 68 and 69 with the earliest being 35th week of 68 and the latest being 21st week of 69.