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An ugly but working HP6060B Electronic Load

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amc184:
I was lucky enough to get a Agilent 6060B for a great price a few years back, and one of the first things I did after fixing* it was to relocate the binding posts to the front panel.  Here's a few images for my unit:


Front panel with binding posts and custom panel I had made.


Inside front panel with posts installed, showing the pre-existing holes for the posts.


Where front panel cables are connected, former location of binding posts at the rear panel.


Overall view of the modification.

Some tips and information I recall from when I did this:

* The front panel has three layers.  On the inside is the aluminium sheet chassis, which has holes ready for front panel binding posts.  Then there is the main front panel plastic moulding, this also has holes moulded into it it, easy.  Then there's an outer aluminium sheet with the button legend label.  This outer sheet is the only bit that needed modifying.
* To make the holes in the front panel I drilled a hole through the rough center with the largest drill bit I has to hand (12mm) for each, then grabbed a round file.  I then used the file to enlarge the holes to match the size of the holes moulded into the front panel plastic moulding.
* I designed and got made a custom plastic sheet to go between the posts and front panel.  This is made of a two layer acrylic - there's a thin outer white sheet with a thicker black layer underneath.  Any laser etched lines or areas cut right through the black layer, with can be used for markings.  I tried to match the style of the original button legend.
* I'm actually in the middle of redoing this panel along with making some others in aluminium.  Aluminium backed PCBs with with white soldermask and black silkscreen achieve a very similar look, but are more rigid.  Now that cheap prototype aluminium backed PCBs are available I've been using these for tonnes of stuff like this (and I'm ashamed to say I haven't made one that has electrical functions yet, just mechanical).
* The 6060B doesn't really need this panel to be mechanically robust.  It's just sandwiched between the bind post and a tightly fitting hole in the front panel.  This is not the case for a 6644A and many other models, where there's a thin label then a plastic moulding with open holes for multiple post styles.
* For this unit and others I've relocated the posts on I try and reproduce hop HP / Agilent did the front panel binding post option.  I think the way I did it is the same, where the original current carrying brackets bolted to the PCB remain and heavy gauge cables are added.  I used a 16mm² cable to minimise the voltage drop, with soldered on heavy lugs at both ends.  I would have liked to crimp these - I don't have a heavy crimper at home, but I do have a soldering iron capable of soldering to 16mm² cable (Metcal MX500).
* I also made a blanking plate to close off the original rear panel holes.
Once I've received the new aluminium backed PCB panels I've ordered I'll check they work, and if so I'll post the gerbers up here for anyone to use.

* I bought this in the US and brought it back to New Zealand, and the first thing I always do it set the voltage selector to 240V.  I was reading the silkscreen and realised that it was in the 240V position already .... no way.  Yeah, that was the whole fault, it had been set like that while they had tried it with a 120V supply.  It was USD210 for a tidy example built in 2007, one of my best test equipment buys ever.

AMR Labs:
Very nice work you did there, and look forward to the Gerber files if your prototype plates work out. Its a good idea, and perhaps even a piece of regular FR4 blank fiberglass PCB might also be strong enough even without the aluminum backing.

One thing I noticed in your pictures is that you set the holes of both posts vertically (where the wire goes into), which would make it a bit difficult to insert the wire into the lower post unless you come from bellow, except for example if the unit is sitting flat on a bench as shown in the picture. In the original 6060B with front panel posts these holes are set to be on the horizontal plane so both wires can easily be inserted from either side of each post.

AMR Labs:

--- Quote from: jwrodgers on January 17, 2023, 02:35:18 am ---Managed to get 2 Black from RS, but they have discontinued the Red ones. A further search led to the same parts, and other 60A binding posts from Cliff Electronics:

https://www.cliffuk.co.uk/products/terminals/touchproof.htm

Seems like an audio-foolery site, but nice terminals :) Hope they don't have audio-fool prices.

--- End quote ---

I saw those generic 60A Cliff posts a while ago on ebay, but I wondered if that 60Amp rating is for real and how good the manufacturing quality really is. Just compare the threaded shaft diameter to the original HP posts and there is a huge difference. I am assuming the original posts must be rated well in excess of the maximum 60Amp that the load can actually handle. But I guess they might still be a better choice than any of the regular run of the mill binding posts out there, as long as they are well build electrically speaking, and are not just bulked up for appearances.

I was close to ordering these to give them a try but then I found the pair of original posts. I just checked and these generic posts are still available on ebay, look at items 401469598445 (red) and 372181908331 (black). At the time I also did find them I think it was at Newark but not sure if they might still have stock left.

jwrodgers:
Thanks, I've ordered a few from RS, and I've been thinking about how some folks here have moved the original posts from the back to the front. I am considering doing that, as it will look pretty original. Then I have to decide if I want to put the new cliff posts onto the rear of the case.

I suppose there is no real need for any posts at the rear if the unit is only being used on the bench and not in a production/rack setup. Also, need to check, but I am sure some mods need done to the sensing circuitry when putting the posts on the front to make sure the sense is picked up close to where the posts are installed, I will have a look in the service manual and report back later.

If I decide to move them, I will think about options for sealing the holes at the back of the case to make it look good. Probably acrylic in grey shade to match case with 'connect input to front terminals' or something similar in the right font :)

AMR Labs:
BTW does anybody else also find it a bit annoying that the 6060B starts the fan at low speed immediately after power on and runs it continuously even without a load even attached? Mine does, and although it is at the lowest speed, I find it still a bit noisy and unnecessary. Is this normal?

So as a test I did put one of those KSD-01F TO-220 N.O. thermostat in series with the fan supply wire and mounted it on one corner of the heatsink under one of the existing screws. The one I used triggers at 55-C but I think I need to lower the triggering temperature as when the fan comes on after some use it is already running at high speed and the air coming out is already quite a bit warm, although not yet too hot. I ordered and already got a replacement thermostat of 45-C and had been waiting to find time to replace it.

To me ideally the fan should just come on after the temperature of the heatsink rises enough to justify it. That would also prevent some premature dust build up, and in my case I live at at an almost constant 70% humidity and about a mile from the sea coast. So constantly pumping air into an electronic equipment without really needing it seems like something I would like to lessen as much as possible. Any thoughts on this?

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