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Linear Power Supply wiring best practices?

levimax

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#1
I am working on a DIY monoblock project using a salvaged transformer. The transformer is 48 volt (58 volt no load) ~ 500 VA from a Kenwood power amp from the 1980's (rated at 150 Watts continuous pre channel both channels driven) . Amp will be approximately 150 watts into 8 ohms and 250 into 4 ohms. I have two questions.

1. The original Kenwood amp used all 20 gauge wire in the PS (for both primary and secondary transformer sections). I have built some amps with new 500 VA Toroidal transformers that are using 14 gauge on the primary and 12 gauge on the secondary. This is a huge difference and doesn't make sense to me... I am sure the engineers in the 1980's knew about wire gauge issues and looking at specs for 20 gauge wire it can carry up to 11 amps so don't understand why the wire is so much heavier now. Is it just audiophile "fashion" or are there some technical reasons to use the heavier wire.

The spec sheet on the toroidal says "These transformers have heavier gauge wires then the normal requirement to avoid the copper lost during the full power output." Reading about "copper lost" I see that heavier wire in the transformer may make some sense but still don't see why the hook up wires needs to be so heavy.

2. The connections on the transformer have the wire "wound" around a pin and not soldered. I was going to solder the new wiring to the pins but then wondered why it was done this way originally. Again the engineers in the 1980's must have had a reason? Is there a reason that "winding" around a pin is better than soldering?

Picture of transformer attached.
 

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RayDunzl

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#2
The connections on the transformer have the wire "wound" around a pin and not soldered.
That's a "wire wrap" connection.

Stick the end of the wire into the bit of a rotary tool, slip the tool over the pin, zap, and done.

It's fast on a production line, and creates a reliable but easily removable "gas tight" connection.

---

One of many Telco Wire Wrap Applications:

1592758722508.png



Manual tool:

 
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#3
As for the ga. of the hook-up wire; the magnet wire copper in the transformer itself no doubt dominates the effective resistance of the supply, as it is hundreds of feet long and 16ga. if you are lucky - so a few inches of 20ga. makes no difference.

Back in the day, I built a lot of TTL logic boards with wirewrap ... and got a few puncture wounds from the stakes. As a technique it is very reliable.
 
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