Vintage amps full of insulated leads?

[mort]

WOW, in a tight little mess like that maybe they use the insulators simply to make it easier to get meter probes in there without inadvertently contacting other components on the way in. Just a wild guess.

[Kazooman]

Yes, these things are a crowded mess. You can see that the old paper caps were in rough shape so I replaced all that I could. To get to one I had to unsolder one end of most of that row of resistors. I will attach another picture that shows my collection. The U-shaped chassis is just that. You can remove the end pieces, but there is no way to get a better approach deep down in. The unit on the right is the one I posted before with some new caps. The unit on the left in the new pic is a slightly more recent vintage model that has PBS in it. Not a really big improvement and they did some really strange things with component placement so trying to trace off a schematic is a challenge. The large silver square at the left end of that one is the tape drive motor. If you look at the rats nest of wires below the filter cap cans you can see that as the OP posted in his last message they use pretty light gauge wire for the B+ (about 380 V). I finally decided I needed to replace the filter caps on that one and this is a work in progress. Both cans hold caps and you can't get them in that size any more. I did find dual cap cans but one is going where the originals were and the other will stand in the middle of the tubes. Not ideal, but just about the only option.

In addition to the electronics there is the tape drive and all the recording and playback heads to deal with. Quite a challenge.

[Tom Phillips]

The use of insulating tubing varied a lot. My take is that some manufacturers instructed their assemblers to use the tubing on every lead because they didn't want to worry about the occasional leads that may short together if the components where later pushed out of their initial position. Other's may have just felt that it was good practice. The assembly line people were just doing their job. They were not designers or techs and they were not left to "make it up" as they went about their task. They needed to work to keep costs down and there was probably significant variation in parts placement.

Another manufacturer may have specified tubing for just a few selected locations where the component leads were long or the routing was difficult.

Manufacturers of higher end equipment would spend more time planning the physical layout and generating instructional documentation for the assembly line staff. They also used assemblers with a higher skill level. Take a look at the attached gut shots of a 1960 Tektronix square wave generator. They certainly didn't feel the need to insulate the leads.

[g1]

Yikes! Looking at some of Kazooman's pics, I sure don't understand why people gripe about repairing pcb amps .
Even something like this
Sure, it looks great, but if I had to replace a socket or that pot at the top right...I'd much prefer replacing a pcboard mount pot or socket.

Wouldn't want that there wire coming off if Nicky desides to launch a few.

who's Nicky???

[Jazz P Bass]

who's Nicky???

Nikita Khrushchev,
Soviet Premier, circa 1956.
Remember him banging the shoe?

[g1]

Ahhh, wasn't thinking "period correct"-ly .

[Rhodesplyr]

Tom,

Thanks for a very thoughtful post. I definitely see what you're talking about in the Premier 120, where some component leads are carefully insulated with tubing, while, at the same time, the ground connection for the speaker output is through the steel chassis--as is most of the amp's grounding. Filament wires aren't twisted at all. In other words, I definitely see someone building this amp following instructions without particular regard for practices that might actually make the amp quieter at idle or ensure lasting ground integrity.

[Enzo]

The thin tubing placed around bare wire leads was called "spaghetti." You could buy rolls of the stuff. An easy way to make it was to strip off some insulation from a piece of 18ga wire or something. SOme of it was stiff plastic, some was woven, like pushback wire. It came in simple fiber, it came in fiberglass, which could withstand high heat.

When things were wired point to point, wire leads crossed each other all the time, so a piece of spaghetti prevented shorts. I think Tom is right, assemblers were simply instructed to sleeve all leads. Now no one has to keep track of which one did or did not need it, and it gave a uniform look to the product.

ANother consideration is that while two leads may be in little danger of touching, someone may have to place a probe from his meter down between things, and sleeving protects that operation from causing shorts.

[trobbins]

But the quirky thing being highlighted is that some groups of wires aren't sleeved, and there appears to be no reason for the unsleeved groups.

[Tom Phillips]

But the quirky thing being highlighted is that some groups of wires aren't sleeved, and there appears to be no reason for the unsleeved groups.

Ahh...But you forgot about the directive that said "all component leads shall be sleeved...except for those that are not."
I don't think that we will find a universal answer to the original question. There was just too much variation from manufacturer to manufacturer.
Cheers,
Tom

[Enzo]

[QUOTE][But the quirky thing being highlighted is that some groups of wires aren't sleeved, and there appears to be no reason for the unsleeved groups. /QUOTE]


Not sure to what you refer. Rhodes never gave us a photo of his. And the sleeving we are talking about is thin insulation tubing around individual component leads, like the two wires coming out of a resistor. Not groupings of wires as in isulated hookup wire.

[trobbins]

Ooops - my comment was biased towards Kazooman's photos showing groups of speghetti protected wires, versus groups without.

[diagrammatiks]

it looks like they insulated leads that looked like they would cross or shift.

cost saving measure.

tek didn't do it for their terminal mounted builds since the components were mounted firmly.

[Tom Phillips]

...tek didn't do it for their terminal mounted builds since the components were mounted firmly.

Yes but notice all the other point to point lead work that uses no sleeving.

[diagrammatiks]

yeah but tek's parts density is way lower then some of those radios.

you can get at everything without risking shorting two wires together with a probe.

:shrug:

they also stopped doing it because the available insulation at the time was terrible and would catch on fire or melt and explode.