Jerry:
Good answer. I agree!
73
Bob K4TAX
Dr Gerald N Johnson electrical engineer wrote:
>
> If the LM2940 is true of all Scouts (its was pin and mounting
> interchangeable with the LM7810 that would guarantee that 12.8 volt
> limit without fuse and connector drop).
>
> 1.1 volt drop through the connector and fuse is unreasonable. One should
> be certain that the fuse is a 32 volt rated fuse rather than 250 volt
> rating. The higher voltage fuse has to use a much longer fuse wire to
> cause a much longer gap to interrupt the load properly and will always
> have a greater voltage drop under load. It might be that the automobile
> industry has learned about voltage drop since they have practically
> universally changed from 1/4" cartridge fuses to fuses with blades that
> fit into female spade connectors.
>
> The round stamped Molex or Molex like connector pins universally used
> for Ya-Com-Wood HF radios are known to occasionally cause voltage drop
> problems. I suspect that may partly come from a manufacturer's
> specifications that are a bit optimistic about voltage drop and partly
> from looseness coming from a user not aligning the pins perfectly and so
> squashing the male pin and expanding the female pin. I've always
> preferred the Jones 300 and 400 series but their (perhaps honest)
> voltage drop claims are higher than Molex stamped pin connectors so are
> hard to justify based on manufacturer's claims alone. The Japanese
> in-line fuse holders are often sources of far more than 1 volt drop,
> likely from the use of high voltage fuses and from sprung brass springs.
>
> Removable connections are a problem. The spade lugs in the old 6 volt
> beetles were a constant maintenance problem. They often were just bare
> brass and not very springy. When there was any electrical problem the
> SOP was to remove and clean each one, squeezing the female side with
> pliers to close the springs tighter. Today Ford and others apply
> silicone grease to connector pins and lamp sockets to slow corrosion
> (Ford pn F8AZ-19G209AA). Perhaps that would be a good idea for radio
> fuse clips and connectors. I did that for all the lamp and spade lug
> connections on my camper last June and so far they are all lighting
> reliably.
>
> Another possibility is the contact grease specified for aluminum power
> connections. There are many brands, the grease is black and filled with
> crystalline zinc which serves to break through surface oxides. I know
> electricians who use that on copper connections (at least on mains) and
> who think it cuts their call backs for heating connections. It can't
> replace a good connection but might help the marginal connections. One
> must be careful to not get it on insulators as it can be a conductor. I
> used it on all the ground connections on my camper last summer. I
> replaced those that depended on the spring pressure of a pop rivet
> squeezing a connection through plastic, with solid metal with stainless
> steel star lock washers and aluminum contact grease. I expect those
> connections to stay for decades with no further care. Time will tell.
>
> The Koolamp company makes a silver filled grease for improving marginal
> connections in power panels. Last time I tried it, the electricians
> globbed it on instead of using it sparingly as they should have. Its not
> especially cheap and thick layers are not much benefit.
>
> I notice the power connector dangling from my latest TM-262 mobile is a
> pair of flat spades, not the stamped round connectors.
>
> Tin contact surfaces will never be as good in the real world of
> basements, cars, and outdoors as silver plated contact surfaces. Those
> silver plated pins can be had for the connectors Tentec uses but cost
> quite a bit more. Oxidized silver is still a pretty good conductor. Most
> other metal oxides turn into semiconductors or true insulators (ala
> aluminum).
>
> One should not only use fuses rated at 32 volts but fuses made only by
> Buss or Littlefuse, not something made in offshore. Buss and Littlefuse
> parts have more attention to detail, such as voltage drop and the proper
> metallurgy so that they blow at the predicted current than offshore
> products sold by the corner convenience store or super import department
> store.
>
> When looking for the minimum voltage drop through a low voltage fuse it
> might be worth looking at the fuses made for semiconductor protection,
> if they can be had in 32 volt versions. The super fast fuse elements are
> generally made of silver, not some lead based alloy and so should have a
> lower fuse element voltage drop. But that may not be true of the 250
> volt rated fuses compared to an ordinary 32 volt lead alloy fuse. The
> silver element fuses will cost ten to 50 times as much as plain 32 volt
> fuses, but will protect finals a little better. However my experience
> with fuses still seems to be that the fastest, most expensive
> semiconductor fuse is still primarily a costly and reliable indicator
> that the semiconductor has shorted. Though the 15 amp buss ATC that I
> use in the cable I made for my TenTec Corsair II has blown a couple
> times before the finals have fried from high SWR loads.
>
> I wonder if a Jones P402 plug would fit the back of the Tentec radios
> without too much chopping?
>
> 73, Jerry, K0CQ
>
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