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Fool for the 8656A Sig Gen
jrharley:
HP 8656A update here, thanks again for all the feedback and support from everyone!
I've been diving in to the attenuator assembly, trying to understand what makes it "tick". I've made some progress, learned how to take the actuator forks out and witnessed first hand the o-ring failure that has been well documented by lazyelectrons. (www.lazyelectrons.com).
All of the remaining actuator forks in my unit have cracking o-rings. We're going to be re-building the entire attenuator assembly, there's just no escaping that. I've been working on how to replace my missing forks, we'll see how that goes. There may be a solution developing as I write this. "I get by with a little help from my friends"....... We'll see!
So, for anyone interested, I'll try to document the re-build here, starting with the attached pics.
JRH
Swainster:
--- Quote from: Brumby on March 11, 2023, 08:08:31 am ---
--- Quote from: Swainster on March 05, 2023, 03:50:45 am ---Hi Brumby, spares unit you say?... Actually my 'B came with a spares unit which is only missing its power transformer (and a burnt out inlet filter). I understand that the previous owner of the 2 units 'repurposed' the transformer for a DIY project. I'd be interested in buying a replacement transformer to complete the unit. That said, posting a heavy item like that to Singapore is probably pretty painful on the wallet.
--- End quote ---
Partially pulled out the transformer. Pictures below. The cut wires were already that way. Weight is over 2kg which puts it into the range of AUD$62 - AUD$68 for basic shipping. (Actual cost will depend on packed weight.) I can include the cover and mounting hardware. I would be inclined to supply as shown up to the DB15, cutting the 4 smaller wires (long enough to be usable).
If you are interested in proceeding, let me know and I'll do some electrical checks.
--- End quote ---
Hi Brumby,
Yes, I'm definitely interested but so as not to distract from the restoration of the 'A' I'll drop you a private message. Or at least, I'll give the PM system a try as I've never used it before.
Swainster:
Hi JRH,
I was just thinking about how I'd have tackled this a few years back, before I picked up CAD. When I was back in the UK I would have just popped out to the shed and grabbed the nearest piece of scrap plastic (maybe a plastic ice-cream tub lid or an old chopping board) and started carving away with whatever tools were laying in the bench. Seems like the fork at least might lend itself to this method of improvisation. The cover might be easier as a 3D print
Tony_G:
I'm wondering if you could, as a test, not long term, get away with just pushing a cam into some modeling clay and then filling the resulting void with epoxy - Little trimming and sanding like Swainster said and you might have something that would at least give you the ability to do some testing while you look for a full long term replacement.
TonyG
jrharley:
I hear you guys, and I've been mulling over DIY fabrication options as well. Anything from direct milling out of plastic stock to resin casting are options.
In studying the assembly though, such an approach would be a heavy lift in order to achieve the precision needed I think. Not impossible, but one would spend a fair amount of time doing 2 forks and a cover, (which holds everything in place very precariously).
I've attached a sketch of how this crazy contraption switches. It relies on an actual deformation of the little gold contacts, to make or break the connection. Pretty wild.
As always, I really appreciate the interest and the feedback!
JRH
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