Insulation for component leads in point to point wiring - diyAudio
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Old 18th November 2015, 09:45 AM   #1
Beer30 is offline Beer30  United States
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Default Insulation for component leads in point to point wiring

So, I salvaged an old aircraft transponder (at least I think it's a transponder). Good for 3 or 4 pots, 4 stepped attenuators of questionable utility, a mess of tubes (about 8, I think) and loads of components.

I don't have any pics right now but I'm wondering if I'm doing point to point wrong. The transponder is loaded with components in a tight space. It appears the manufacturer cheated and put insulation on the bare component leads where they didn't want unintended contact. I haven't dug into it too deeply but I'm assuming it runs on the 24V batteries that are common in most light aircraft of the era.

The question, can I get some insulation for my bare component leads and considerably ease my voltage/arcing component placement anxiety or is this a case of OK for 24V, horrible idea for 300+V?

My amp chassis seems it would be a bit tight but insulating component leads might save this hack some grief when I put power to the circuit. Can't say I've seen it on here before and a quick google search on the site didn't pop anything that looked similar.

I'll post some pics if I can manage to figure it out.

Set me straight.
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Old 18th November 2015, 10:48 AM   #2
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A lot of people do it and it is a good safety measure, both to prevent unintended shorts during operation and also to make it harder for you to touch high potential wires during testing/servicing/debugging.

When I want to dress component leads I strip off the insulation of a normal 600V rated cable and cut to length. I may lose some of the bare copper but this way I know the insulation is good up to the hundreds of volts range.
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Old 18th November 2015, 12:54 PM   #3
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Firstly, with 24V and tubes, the h.t. is likely to be vibrator-increased to some 200 - 300V, or some other voltage increasing means.

Even then: Unless there is going to be considerable bashing and shaking with impractically thin component leads, such voltages compose no risk by arcing, in air. I do not have a figure right now, but arcing over <1mm would require a kV or more. (Been there, tested that.) That is not to say one should not provide a safety factor, but arcing would be the least of your problems - under normal voltages!

PS: OOPS! Sorry! I meant >1mm

Last edited by Johan Potgieter; 18th November 2015 at 01:03 PM.
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Old 18th November 2015, 01:15 PM   #4
DF96 is offline DF96  England
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Aeronautical electronics requires somewhat greater reliability in the face of vibration than domestic audio. If it was military it might need to continue operating with a few bullets rattling around inside the chassis, or after being dropped a few times.
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Old 18th November 2015, 01:28 PM   #5
JMFahey is offline JMFahey  Argentina
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^^^^^ that.
Military equipment, doubly so if airborne, often needs to be VERY compact and that is an understatement, so they can't separate parts leads properly.
But on homemade or standard audio equipment, you don't NEED to do that.
Unless building a Tube pedal or something inside a tight Hammond box or similar ... but I guess it's not the case.

In my youth (think late 60's), one common source of small allowance only budget Electronics stuff was buying surplus Military equipment, WW2 vintage, and modding/cannibalizing it.

Disassembling was a PITA, all parts had legs tightly wrapped around posts or inside terminal holes 3-4 times before soldering, all wiring wast tightly wrapped in waxed multicoloured string, accessing anything meant removing 50 screws (or so it seemed ) which were glued in place against vibration, the works.

But what FUN !!!!!!
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Old 18th November 2015, 02:11 PM   #6
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Quote:
Originally Posted by JMFahey View Post
In my youth (think late 60's), one common source of small allowance only budget Electronics stuff was buying surplus Military equipment, WW2 vintage, and modding/cannibalizing it.

Disassembling was a PITA, all parts had legs tightly wrapped around posts or inside terminal holes 3-4 times before soldering, all wiring wast tightly wrapped in waxed multicoloured string, accessing anything meant removing 50 screws (or so it seemed ) which were glued in place against vibration, the works.

But what FUN !!!!!!
AMEN!!

What memories, friend! (For your own sake, you hopefully a bit younger than myself! Still ...) Yes, money was scarce my side, and these surplus Military stuff afforded endless joy. One also got invaluable training form investigating such, putting me ahead of many others for life.

Thanks for memories!
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Old 18th November 2015, 05:09 PM   #7
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This is a typical production/rework/diy commodity widely known as 'spaghetti.' Personally I often use it just for added peace of mind regarding safety and reliability. Other times it's a necessity.
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Old 18th November 2015, 09:10 PM   #8
Beer30 is offline Beer30  United States
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Thanks for all the responses. I consider myself enlightened and maybe the next person with the same question will find this in the search!
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Old 18th November 2015, 11:38 PM   #9
lexx21 is offline lexx21  United States
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I use teflon tubing in areas where there is a possibility of the wires touching. Cheap, find it on the "bay" for about 10 bucks or so, and it works well. It fits the leads of the K40 caps perfectly.

Like was said above though, most of the time you really don't need to use something like that. I only use it if I am standing a cap in the vertical position and want to insulate the lead coming back down. The Russian caps that I use don't have a poly coating around them, so a short could be a real possibility with those.
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Old 19th November 2015, 11:26 AM   #10
M Gregg is offline M Gregg  England
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I use PTFE sleeving,

It doesn't melt if a component gets warm. And it doesn't melt when you solder the component.
As above it's not really needed, however if for some reason I use a long resistor lead to connect somewhere then its insulated.
Ie I might use a resistor with short connection to an audio circuit but have the other lead long connecting to Gnd or B+.

I might use it to stand off a component from a board or even sometimes ceramic beads. Depends on the temperature.
I sometimes strip off standard mains solid core PVC and replace it with PTFE I do this anywhere where there may be a warm environment and I am using any current and want some solid core copper.

I'm not a fan of PVC inside tube equipment..or anything that gets warm. Old PVC was also effected with solvents and cleaners.

NB remember components can be dissolved with some cleaners<<Plastic radios come to mind..
The old plastic tuning caps..weld very nicely and you don't even have to be there for it to happen..spray and walk away..
Watch the radio glue itself to the bench as well..LMAO

So when you clean sockets etc take a moment to look at whats under the socket and if its going to dissolve..

PVC is also known for the plasticiser to leach out and you can even get reactions between insulation and component parts..take a look at polystyrene and PVC as an example. (So sleeving a polystyrene cap with PVC insulation is not a good idea)

http://www.generalcable.co.nz/getatt...r-Bitumen.aspx

I have also seen reactions between some cable types and grommet material. Wires and tar is another example<<<used sometimes in old potting of components.

Regards
M. Gregg

Last edited by M Gregg; 19th November 2015 at 11:52 AM.
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