450V DC cables & connectors..?

[mcgruff]

I'm trying to design a modular system to cut costs which puts a rectifier, a set of transformers and a couple of power stages in one box so they can be shared between different amps. This "big box" would pass high voltage DC straight off the rectifier to a smaller box which contains power supply circuitry and preamp. The smaller box would feed B+ nodes (power tube plates, screens, and phase inverter plates) back to the bigger box.



I'm a bit of a noob at amp building so I'd like to ask for some advice about passing high voltage DC back and forwards like this. 6V heater supply I think must be in a separate, screened cable. Are there any lead dress issues with the power tube plate, screen, and phase inverter B+ together in one 3-core cable? Also, can I put rectifier DC and ground together in one 2-core cable?

If this is viable I was thinking about speakon connectors but it looks like they can't handle such high DC voltages. Any suggestions what I could use instead?

Incidentally, this whole plan started when I couldn't decide between a Matchless Spitfire or a 5E3 Deluxe. Funds are tight so I can only build one. Then I realised I could share transformers to cut costs. Then I discovered the \13 CJ11 shares (almost) the same power stage as the 5E3, and the Goldtone GA15 power stage is near identical to the Spitfire. Also, if you're building a Spitfire, it's fairly simple to add a Lightning option as well.

So that's five great amps. If I can find more designs which can all use the same transformers and power stages a modular design makes a lot of sense. Adding a new amp just means building a relatively simple preamp and power supply circuit, dramatically cutting costs and workload.

If not, I'll just put the above in one big box.

[Shadrock2]

I have an old (non functioning) McIntosh 50W-2 that uses a separate power supply from the amp unit and it uses a male octal type connector that plugs into an octal tube socket in the power supply section. That seems like a fairly safe way to hook up a rig like that. Don't know whether an octal plug like that is still available. It runs all the supply nodes and ground through the cable.

[mcgruff]

Great tip - thanks. A quick google turned up a few octal plugs.

Also good to get some evidence of supply nodes running alongside each other in one cable.

[Gingertube]

If you need to look for modern high voltage capable connectors then LEMO Connectors is the manufacturer to look at.
I use them in the day job.
LEMO Connectors | Push-Pull, Circular Connectors | Cables
Cheers,
Ian

[eschertron]

Another maker of those industrial-grade disconnects is Amphenol, there are probably several others available through Mouser or Newark.

As an alternative design, Randall makes (or made) amps with replaceable preamp 'cartridges' so the user could pull out his matchless clone and slide in a 5E3. I've also seen inside a Duncan Convertible; the 'convertible' tube modules slide into simple edge connectors. I have no idea what the voltages applied were, but the stages were set up like normal guitar amp triodes, with 100k Rp and 1.5k - 2.2k or so Rk values.

[Enzo]

I am a fan of the AMP circular connector line for things like this.

[mcgruff]

Great It's very easy to get stuck on little things when you're learning so all of these suggestions are a great help.

@eschertron

A cartridge design would be much neater. I'm not planning to gig with it though and lots of little boxes joined up with cables is less of an issue if it's just going to sit on a bench for home / studio use. More importantly, I feel a bit more confident about creating a solid connection with some of the socket types mentioned - not that modular is a bad idea just I'm not sure how to do it well. High voltage connectors have to be done right...

[nashvillebill]

A ton of hifi consoles were made in the 50's using Molex (or similar) connectors to carry B+ and heater voltage from the main amp to the preamp/tuner. They worked fine then and they're still functioning today.

Speak-on connections can carry some pretty high current, too, 20A to 40A, I bet's that's more than your heaters will draw!

[mcgruff]

I looked at Speakon. Current wouldn't be a problem and they can handle 240VAC but I couldn't find a DC voltage rating. The transformer I'm using puts out 300/300 so I probably need a minimum of 400VDC.

[trobbins]

If you are connecting and disconnecting energised DC (and AC) then you do have a problem with arcing causing aging problems. Some form of mechanical interlock with a power switch would be ideal (ie. the connector cannot be pulled out or pushed in if the power is on) - that could be done perhaps with a 'sliding door' of some kind, or a solenoid locking pin type - probably diy, as any industrial solutions I can recall are 'large'.

[mac dillard]

Chris Hurley the administrator of the AX84 site did a lot of work on this situation a few years back. You might try contacting him and see if he will share his info.