[ARC5] Signal generator selection

[Tom Lee]

Although HP doesn’t guarantee it, I’ve never seen an 8640 fail to get to 455kHz. But if by chance you encounter a rare one that doesn’t quite make it, or if you want to extend downward a few more kHz, it’s an easy mechanical tweak to get there. But you bring up a great reminder that those who are working with receivers that have lower IFs won’t be able to use the HP8640.

Cheers
Tom 

Sent from my iThing, so please forgive brevity and typos

> On May 5, 2021, at 15:25, Sean Barton <seanbart at fidnet.com> wrote:
> 
> There is a fellow in India who has been reproducing the gears in brass and selling them on eBay.  A set will cost you $55 plus shipping.  I bought a set but haven't installed them in my 8640B yet.  Another drawback to the 8640B is it only goes down to 500 kHz but can be coaxed down to about 450 kHz.  HP came up with a scheme to use the 5 MHz reference and mix it with the RF output to get lower frequencies.
>  
> Sean W0KPX
>  
> -----Original Message-----
> From: "Tom Lee" <tomlee at ee.stanford.edu>
> Sent: Wednesday, May 5, 2021 4:26pm
> To: "Hubert Miller" <Kargo_cult at msn.com>
> Cc: ARC5 at mailman.qth.net
> Subject: Re: [ARC5] Signal generator selection
> 
> Short answer: Very prevalent. HP chintzed out on the plastics — the gears are actually nylon.
> If they’re merely cracked, they’re repairable without too much drama. Getting them out is a bit of a pain, but just from the number of steps. Not too complicated, just time consuming. Once they’re out, you can enlarge the center hole a tiny bit, then reglue the crack. I leave a wire “tourniquet” in place to help keep everything together. You can finish the entire set of gears in a weekend.
> The brass replacements are superb, so if you can get them, they’re worth it.
> Another congenital problem is the tendency for the little contacts to fall off. If they’ve fallen off into the unit, great — you can superglue them back in place. Otherwise, you’ll have to make your own (easy enough: I’ve scrounged suitably springy stuff from edge connectors). Again, disassembly is a little time-consuming, but no one step is particularly difficult. I’d do the contacts and gears in one go, so you only have to pay the disassembly overhead once. Even if the contacts are in place, I’d still put a drop of superglue on them all, to make sure that they stay that way.
> — Cheers,
> Tom
> 
> 
> Sent from my iThing, so please forgive typos and brevity.
> 
> On May 5, 2021, at 1:27 PM, Hubert Miller <Kargo_cult at msn.com> wrote:
> 
> How prevalent is the plastic gears breaking?
> Are there practical replacements, like has anyone produced 3D printer replacements?
> Are these gears extremely difficult to remove, or merely difficult?
> tnx
> Hue Miller
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