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Sets, Parts and Service Information Wanted (private buyers only, no swaps) If you need help obtaining components, sets or equipment, post a message here. Private buyers only - no traders. No swaps.

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Old 10th Nov 2018, 11:42 pm   #1
GW4FRX
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Default Seeking screw insulator...

A Radford amplifier I'm restoring uses nylon screw insulators to isolate the output device heatsinks from ground. The originals had an outside diameter of 3/8in and a body diameter of 1/4in. Unfortunately all four of them are extremely brittle and one is cracked right across the body.

The nearest modern equivalent is a Silfox CAJ005D which conforms almost exactly to the imperial dimensions. Unfortunately they're only available from RS in multiples of 100 and a bag costs 44!

If anyone has four of anything like this in the spares box looking for a good home, I'd be very happy to buy them.

John
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Old 11th Nov 2018, 6:57 am   #2
60 oldjohn
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Default Re: Seeking screw insulator...

Car number plate nuts and bolts ?


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Old 11th Nov 2018, 10:08 am   #3
Bobdger
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Default Re: Seeking screw insulator...

Please can you give us the RS part number?.
Thanks.
Bob
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Old 11th Nov 2018, 10:10 am   #4
Station X
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Default Re: Seeking screw insulator...

Quote:
Originally Posted by Bobdger View Post
Please can you give us the RS part number?.
Thanks.
Bob
A simple Google search on "Silfox CAJ005D" found this:-

https://uk.rs-online.com/web/p/screw...ators/2031321/
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Old 11th Nov 2018, 10:28 am   #5
robinshack
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Default Re: Seeking screw insulator...

Those in rs link are 2.2mm long.
Is that rs item really what you want John?
If so, I will dig around.
Rob
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Old 11th Nov 2018, 10:40 am   #6
turretslug
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Default Re: Seeking screw insulator...

I can send you some NOS ex-US military maintenance stock T03 insulator bushes, assuming that this is what you're looking for- ivory colour Nylon, shoulder approximately 10mm diameter (slightly over 3/8"), mounting hole 1/4" diameter, centre hole is M4 clearance. The reason I ask is that the Silfox hardware mentioned has an unusually large 4.8mm fastener clearance, which implies early Ge single fastener power devices and not TO3.

I've always used M4 (or 4BA when equipment-appropriate) hardware for securing T03 devices, but there seemed to be a trend towards M3 (or even 6BA) and the insulating kits currently available invariably reflect this unfortunately- possibly it saves a sliver of a farthing per unit on a big run?,

Colin
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Old 11th Nov 2018, 11:49 am   #7
barrymagrec
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Default Re: Seeking screw insulator...

Quote:
I've always used M4 (or 4BA when equipment-appropriate) hardware for securing T03 devices, but there seemed to be a trend towards M3 (or even 6BA) and the insulating kits currently available invariably reflect this unfortunately- possibly it saves a sliver of a farthing per unit on a big run?
Me too but I think the modern tendency is to insulate the screw as well, hence the smaller bush - makes it a pain to connect to the case though.

The last time I needed to mount TO3 devices I turned up some bushes to suit 1/4" mounting out of 3/8 peek rod - bit tedious though.
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Old 11th Nov 2018, 4:29 pm   #8
David G4EBT
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Default Re: Seeking screw insulator...

Quote:
Originally Posted by Station X View Post
Quote:
Originally Posted by Bobdger View Post
Please can you give us the RS part number?.
Thanks.
Bob
A simple Google search on "Silfox CAJ005D" found this:-

https://uk.rs-online.com/web/p/screw...ators/2031321/
They're the ones that John referred to in his first post at 44p each Graham, but as he said, the minimum order quantity is 100 = 44.00 + VAT. (=53.00). The picture at the link is a bit misleading, as the body length is far taller than that of the rather poor sketch beneath it, which states that it should be 2.2mm (3mm total height), but it does say that the picture is 'representative of the range'.

I don't know if these would suffice dimensionally, at 2.85 for a bag of 50:

https://uk.rs-online.com/web/p/screw...ators/0178658/

Datasheet:

https://docs-emea.rs-online.com/webd...6b8150238b.pdf
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Old 11th Nov 2018, 10:16 pm   #9
turretslug
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Default Re: Seeking screw insulator...

A quick check of that RS link shows that they also do M4 and M5 clearance types of various lengths that give the OP plenty of options. I shall certainly bear them in mind for when the current TO3 bushes run out.
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Old 12th Nov 2018, 8:04 pm   #10
GW4FRX
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Default Re: Seeking screw insulator...

Firstly my sincere thanks to everyone who replied to this. Several people pointed out in PMs that suitable devices were readily available on eBay. I also hadn't put it together that TO-3 bushes were usable in this particular application, and four were duly found in the junk box.

There are indeed possible alternatives in the RS catalogue and I did investigate them but none of them offered the combination of ID, OD and bush length required for this particular application. Quite why the Silfox ones are so expensive is unclear -- you can buy the almost exact equivalent on eBay for about a twentieth of the RS price!

Once again my grateful thanks to all for the suggestions. Problem now solved...
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