HP 8640B brass gears

[Skywave]

Whilst my 8640B is partially dismantled and undergoing a few repairs, seems to be good opportunity to replace the nylon / Delrin gears in the A9 freq. range / fm control ass'y., since although they are functional, there are cracks in them. I have heard that brass gears are available - but from whom and where? Is there a U.K. source?

Al.

[MrBungle]

Yes there's a guy in India selling them. I think a set is about 70 USD.

https://www.ebay.com/itm/154054911606

[Mike Phelan]

Possibly:

sales@hpgears.com
www.hpgears.com
01246 268080

No connection with them, but 2 inch thick catalogue!

Please note that this information was from five years ago.

[Humber888]

Al, there is still a guy, I think, in the USA who makes new gear sets from brass and can be contacted via the HP/Agilent/Keysight test gear repair forum. They were very well made but pricey at maybe $300 a set. How bad is the cracking on your gears? If you only have minor radial cracks with no teeth missing, you might get away with using heat to relax the plastic sufficiently on the brass spindles to use Loctite All Plastics superglue to repair the cracks. This certainly worked on my 8640B. If you wish to discuss further, I am happy to do so by PM or phone.

Mike

[Skywave]

Thanks everyone for your suggestions.

When you have a problem such as this, it's always a good approach to investigate as many potential routes to a solution that you can find: the above suggestions are, therefore, apposite.

Many years ago, I did repair an 8640B for a friend that had this classic broken gear problem by using 'superglue', a.k.a. ethyl -2 cyanoacrylate adhesive: that 'repair' never came back; I kept in touch with the owner over a few subsequent years.
So, armed with that experience and result, that is the 'fix' I will now try. If that fails, one of the above suggestions will then be tried.

This problem is one of several that I have encountered in repairing this S.G.: other threads in this section refer, q.v. Hopefully, when (if?) all repairs are successful, I shall deliver a complete write-up. The intention of that will be simply to record what I did to fix said faults - the idea being to assist other owners of this S.G., which is rightfully popular.

Al.

[factory]

These are the brass gears I have (still waiting to be fitted), now I've moved some of my test equipment into storage I now have enough room to actually work on the larger items of test gear including my 8640B.



David

[Nymrod121]

Paul Koretko is the gentleman over in the States; I've spoken with him on the phone & he's still willing to supply. Happy to PM his contact email/phone number if needed.
Guy

[Humber888]

IIRC, the plastic used for the gears is of the 'greasy' type that normal superglue does not bond well. That's why I mentioned the Loctite All Plastics version which really does work. Probably teaching you to suck eggs!

[Skywave]

'Superglue': I didn't realise that there were so many variants made, all based on a common theme. The following extract from Wikipedia makes interesting reading . . .
https://en.wikipedia.org/wiki/Cyanoacrylate.

Al.

[Skywave]

Originally Posted by Humber888

IIRC, the plastic used for the gears is of the 'greasy' type that normal superglue does not bond well. That's why I mentioned the Loctite All Plastics version which really does work. Probably teaching you to suck eggs!

That helpful post does deserve a response - supplementary to the general information revealed in my post immediately previous to this one.

But I know what you mean by 'greasy plastic'. My knowledge of chemistry & polymers etc. is not up to the required level to be more descriptive.
Consequently, you're not "teaching me how to suck eggs!" at all! [How did that saying arise in the English language, anyway? No answers to that, here, please, to avoid going off topic].
In conclusion, I will say - which may be of interest to others - is that the 'Superglue' which I have found to be really effective is sold under the trade name of 'Hard As Nails'. Works really well on the 8640 gears.

HTH.
Al.

[Skywave]

One combination gear (the dual one: straight cut & bevel edge) now purchased; waiting for its delivery.
The other gears appear to be O.K.

Al.

[MrBungle]

Let us know how it goes. I have avoided buying an 8640 twice now due to this risk

[Skywave]

Originally Posted by MrBungle

Let us know how it goes.

Will do. I've just completed a report on my problem of 'The displayed frequency is wrong', q.v.

Al.