Dave Richards AA7EE

October 21, 2015

How Do Lacquered Boards Stand Up Over Time?

A query I hear from time to time about using copper-plated boards for Manhattan construction is what they look like after a few months or years. “How do they age?” is the question. My first such project, the WBR, was housed in an enclosure made from double-sided PCB material, and I could see that the outer surface had developed a bit of oxidation; a certain patina, if you will. My later projects weren’t made from this double-sided PCB – just single-sided, so I was going to have to open them up to see how they’d fared. Comparing how they looked, and remembering how I’d applied the lacquer to each did help in coming to some conclusions.

First of all, this is how the outside of the WBR looked shortly after I finished building it just over 4 years ago. It was already showing a few early signs of oxidation. However, it did fit together very well, and made quite a handsome enclosure –

The WBR in July 2011

I made 2 mistakes with this enclosure. Firstly, although the initial cleaning of the boards was done with Scotch-Brite scouring pads, the final cleaning was with Tarn-X. I later found that copper boards cleaned with Tarn-X develop streaking and oxidation. The streaking on this WBR enclosure was not anywhere as near as bad as I have seen with other boards, but it is definitely there. You can see it on the side panel in the next shot. The other mistake was to spray the lacquer too lightly. I was cautious about spraying it too thickly and causing it too pool, so I erred in the other direction instead. This is what it looks like from the outside today. Not bad, but definitely aged. You can see the areas on top where my fingers press against the case when I pick it up –

The WBR today (Oct 2015)

Here are a few more.

Before (July 2011) –

The WBR today (Oct 2015)

and today (Oct 2015)  –

The WBR today (Oct 2015)

The WBR today (Oct 2015)

If I were making the WBR again today, I’d stay away from the Tarn-X, and apply slightly thicker coats of lacquer.

Next, I decided to open up The Rugster. It was a little direct conversion receiver I had made by teaming up a standard NE602-type DC receiver front end with NM0S’ Hi-Per-Mite filter, set for maximum gain, so as to provide both 50dB of gain and narrow filtering. I built it into an enclosure made of single-sided copper-clad board on a red laminate. It had a really cool and compact look –

The Rugster in July 2012

It still looks the same from the outside today, but I was curious to know what the interior looked like. This was what it looked like when freshly-built 3 years ago, in Aug 2012. The treatment of the VFO toroid was my first ever attempt at using a hot glue gun, by the way. I am more skilled at it now. This particular toroid looked a bit of a mess –

The Rugster today (Oct 2015)

The same view today (Oct 2015), looking remarkably good. You can see that I added a high-pass filter on the back panel set to block signals from the AM broadcast band –

The Rugster today (Oct 2015)

I do remember that I sprayed slightly thicker coats of lacquer than on the WBR, leaving each coat for about an hour before spraying the next coat. Here are some more “after” shots –

The Rugster today (Oct 2015)

In the next one, the brighter patch on the red front panel is a splash of morning sun, and not a discoloration of the laminate –

The Rugster today (Oct 2015)

The 3rd project to be given a second look was the VK3YE Micro 40 DSB transceiver, which I built 2 years ago, in Oct 2013. Back then, the innards looked like this –

The VK3YE Micro 40 DSB Transceiver in Oct 2013

A couple of days ago (Oct 2015), it looked like this –

The VK3YE Micro 40 DSB Transceiver today (Oct 2015)

The VK3YE Micro 40 DSB Transceiver today (Oct 2015)

I used to clean my boards with Scotch-Brite pads but now find that fine steel wool scouring pads work even better. Then, when they’re clean, I dry them with clean bathroom tissue, making sure to blow any loose fibers off afterwards. Then I spray the first coat of lacquer. To this day, I still don’t always judge it correctly, and end up with boards that don’t age too well, but IMO, it is best to spray until it is just beginning to pool, ever so slightly. At this point, the lacquer is quite thick, but will smooth out before it dries. An hour later, you can spray the second coat. I’ll leave it up to your judgement as to whether you apply a 3rd coat (I usually do). From my experience, this way works quite well. I’ll be interested to hear details of anyone else’s experience with lacquering.

In the next post, I’ll talk a little about the methods I use when constructing Manhattan boards.

Advertisements

October 6, 2015

Some More Sproutie MK II Videos

Since finishing The Sproutie MK II and publishing the blog-post on it a few weeks ago, I have been listening to it, winding an extra coil or two, and also attempting to tweak the active audio filters. Coverage of The Sproutie is now up to 18.3MHz, and while I know from previous experience that it will cover up to 30MHz, I am going to leave the upper limit where it is for the time being. Any new coils will most likely be wound for more limited coverage on specific bands under 18MHz. PS – I just spent part of the morning testing out the upper limit of the newest coil by listening to SSB on 17M, and it’s working great – quite stable too.

I had wanted to give the CW and SSB active audio filters more gain, to compensate for the fact that in those modes, the RF gain needs to be wound down to prevent oscillator pulling. Because the narrower filters, even if they have the same gain as the wider filters, give the perception of lower volume, I wanted to design them with higher gain to compensate. Currently, the narrowest filter, a 700Hz low-pass, has a gain of 20dB. I tried building 700Hz low-pass filters with gains of 46 and 34dB, but they both oscillated, putting out a square wave with 10V amplitude at a frequency of somewhere in the region of 100-150Hz. I made sure to keep the Q below 3 – in fact the highest Q stage in the 34dB filter was just a little over 2, but this didn’t help any. For the time being at least, I have decided to keep the current filters as they are. If you view the videos, you’ll see that The Sproutie does indeed work on SSB and CW. If receiving a weaker station for which the set could use a little more gain, plugging headphones in helps and at this point, it’s a compromise I’m willing to make. Trying to build the perfect regen is a rabbit hole from which it sometimes feels as if there’s no escape, so I decided to draw a line in the sand and leave things as they are.

Once again, I feel as if I should apologize for the quality and resolution of these videos. I just entered the 21st century a few months ago with the acquisition of my first smartphone, a first generation Moto G. It’s a budget model, so doesn’t have the best video. It is an improvement on the videos I used to post from my decidedly old Canon Powershot A80 though. The one thing the videos do achieve, I think , is to give you some kind of feel for what the receiver is like to operate. For detailed views, the still photos are the way to go.

This one shows how a regen, if you nudge it into gentle oscillation, can provide some carrier injection for reception of weak AM stations –

Here’s the 25M SW broadcast band –

And another video on the 40M amateur band on CW and SSB, with a special brief guest appearance by Jingles the blind kitty –

Blog at WordPress.com.