McIntosh C-4 and C-8 Umbilical Cord 170-036 No Longer Available From McIntosh

tcdriver

tcdriver

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The title tells the story. The umbilical cable with octal plugs on each end is "no longer available and there is no replacement." according to Brian Scott at McIntosh Laboratory, Inc.

One might think that building a replacement cable would not be too difficult, however; the diameter of the octal plugs are different. The end that connects to the preamplifier has a diameter of approximately 28mm while the octal plug on the other end has a diameter of about 32mm. The smaller diameter plug will fit the clamp/holder on the preamp and the other end will not. The clamp is important because it reduces the possibility of the plug coming loose leaving exposed pins with possibly deadly voltage present.

My questions:
  • Is there a good source for the original cables at a reasonable price?
  • Is there a good source for the 28mm diameter octal plugs?
  • Are there other solutions for making the power supply / preamp connections?
Thanks

image showing the two different octal plug ends:
170-036 (2) (800x736).jpg

Image showing the cable and cable clamp on the preamp:
170-036 (1) (800x498).jpg
 
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The real problem I'm sure is the special sized plug availability, those plugs have been out of style for decades, when the stock was depleted they were gone. The tooling to mold those plugs went to the scrap yard decades ago, it would cost a fortune to have new molds made. Not gonna happen.
So if you need a cable, get it now.

BillWojo
 
BillWojo said:
The real problem I'm sure is the special sized plug availability, those plugs have been out of style for decades, when the stock was depleted they were gone. The tooling to mold those plugs went to the scrap yard decades ago, it would cost a fortune to have new molds made. Not gonna happen.
So if you need a cable, get it now.

BillWojo
Click to expand...

Bingo! One of the downsides of vintage audio. We can't expect manufacturers to stock obsolete parts forever.
 
tcdriver said:
I am thinking about hard wiring the cable at the preamp end. That is what Heathkit did on the WA-P2 and what Dynaco did on the PAM-1.
Click to expand...
That sure looks like a tube socket ending. Have you tried it in an octal tube socket? If it fits, should be no problem to make something. They make all kinds of sockets and adapters for octal tubes.

-Geoff
 
SomeGeoffGuy said:
That sure looks like a tube socket ending. Have you tried it in an octal tube socket? If it fits, should be no problem to make something. They make all kinds of sockets and adapters for octal tubes.

-Geoff
Click to expand...
I just measured a standard tube octal base. It is much too big. :(
 
$200 is pricey, but it’s simply supply and demand. Another idea would be to get one 3D printed. It looks like the old plugs were Bakelite material, which is very different from the materials used in 3D printers. Bakelite is a chemically setting plastic, and cannot be reground, melted, and injected again. Bakelite is also long gone from the market due to its toxicity. If the plug doesn’t get hot, I would assume a 3D printed version would be fine. You would need to pay someone to draw a 3D CAD model of the plug, have someone make the pins, solder the wires to the pins, make a nest to hold the pins, then try to print over it. That would likely cost way more than $200, and take a long time.
 
tcdriver said:
The title tells the story. The umbilical cable with octal plugs on each end is "no longer available and there is no replacement." according to Brian Scott at McIntosh Laboratory, Inc.

One might think that building a replacement cable would not be too difficult, however; the diameter of the octal plugs are different. The end that connects to the preamplifier has a diameter of approximately 28mm while the octal plug on the other end has a diameter of about 32mm. The smaller diameter plug will fit the clamp/holder on the preamp and the other end will not. The clamp is important because it reduces the possibility of the plug coming loose leaving exposed pins with possibly deadly voltage present.

My questions:
  • Is there a good source for the original cables at a reasonable price?
  • Is there a good source for the 28mm diameter octal plugs?
  • Are there other solutions for making the power supply / preamp connections?
Thanks

image showing the two different octal plug ends:
View attachment 2639859

Image showing the cable and cable clamp on the preamp:
View attachment 2639863
Click to expand...
What was the purpose — and the advantages — of the octal cables?
Why did caused them to go away?
 
aucjo01 said:
What was the purpose — and the advantages — of the octal cables?
Why did caused them to go away?
Click to expand...
The preamp didn't have 12 volt filament transformers, so the amps could supply it to the preamp, and they also were an audio connection (In addition to a regular RCA).
Even with a filament transformer you needed an octal plug to connect it.
IMO price and availability of hardware caused them to go away. They are only used with mono equipment....
 
Last edited:
Possibly, a failed power tube, rectifier tube with the glass removed, and the tube`s wires unsoldered and removed using a created, or something repurposed to cover attached to the old tube`s bake lite base, is how I would consider to try, if my purchased used in 1975 C8/C8S preamp, MC-30s package were purchased without the factory umbilical jumpers included, just have to be DIY creative, if non are available, or if considered too pricy.
 
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