I've decided to try making this "budget" SSB project from EA December 1970, which failed to work the first time round when my Dad and I attempted to build the kit; it's not the kind of project that's likely to be successful without test gear handy, something which the designer Ian Pogson glosses over in the original article. It's a double-conversion set with a 4-8MHz tunable first IF, covering from 550kHz to 24MHz in 4MHz-wide bands. Second IF is 455kHz and uses three of those little red box ceramic resonators from Murata. (That bit I've already built and tested.) The 4-8MHz band is direct, the others via a fixed first oscillator (not crystal, but could be made so easily) on 4, 8, 12, and 16MHz. There are going to be a couple of nasty spurious signals at 4 and 8MHz, that seems unavoidable; hopefully the direct 4-8 range can be made to cover the unusable areas of the adjacent ranges. One thing I can improve on is the uncalibrated manual RF tuning, which needs an accurate dial and a slow-motion drive, otherwise you don't know if you've tuned in on the correct frequency or an image. The top RF tuning range is 8 to 24MHz, four whole 4MHz bands on one small unmarked knob! Please bear with me on this project, because it's at my limit of understanding and I'll have a few questions to ask.

EA 160 SSB Receiver Circuit Diagram

OK, the first question. I know that in an audio amp it's usual to earth the circuit to the chassis only at the at the input connectors to avoid hum loops. In an HF receiver, do you instead earth each circuit tagstrip to the nearby chassis, and not bother with a negative wire from the power supply? It's hard to tell how they've arranged this in the prototype.

I was taught to always keep the number of chassis common earthing points to one (star connection), on the basis that every such connection has a resistance and variations in resistance create ground loops and associated noise.

I should add that wire lengths need to be minimised, too, so component placement is also a design issue.

If most of the circuit is built on tagstrip I'd use the mounting terminal of each strip as a local ground point. As long as you are using a metal chassis, there will be no issues in doing this. Running a separate 0v line to the tagstrips will probably introduce instability into the circuit due to all the extra stray inductance and capacitance of the various 0v wires.

Photo and circuit diagram uploaded.

I've completed and tested the RF strip, and this part has problems. The fact that it's far more sensitive at 1 MHz than 24 MHz isn't surprising, but the gain is so high at 1 MHz it oscillates. The 47 ohm resistor across the aerial winding of L1 was obviously added to stop this, but there's still a big peak in the middle of the MW band. Maybe it'll be OK once the AGC is working and the strip is earthed to a chassis. I've changed the 100 pF coupling capacitors to 10 pF and 20 pF to reduce the gain on MW.

The three RF coils were a bother, all of them needing turns taking off to tune properly, and then more turns needed removing once they were on the tag strip because they are so close to each other. I couldn't get the original Ducon ferrite toroids, so I used Neosid 19mm F25 type, which are the same material and roughly the same size. L1 for 0.5 - 2 MHz really needs to be in an earthed can, but I'll see how it all pans out before changing things too drastically. One reason for making this project is to find how well it works when built to spec. I think I can get away without slow motion on the RF tuning, but it will need some marks to indicate the tuning frequency.

I tried to look for errors and errata for that project, but cannot even find the original article in the EA index on the SC site. I guess that index is deficient.

The original article can be found through.

http://www.hrsa.asn.au/hrsa-files/ea-rth-index-090512.pdf

Dec 1970 EA Pg 72, The EA 160 communications receiver. .5 – 24MHz Ian Pogson.

Back in those days of typeset printing technology many of their projects contained errors and omissions that were reported months afterwards.

The index to Silicon Chip projects helpfully includes references to errata published, but the EA project index lacks that and looks to be very incomplete.

I haven't seen errata for this project, but I've not many issues from 1971 where you'd expect to find them.

Photo uploaded to Post 6.

Okay, I've blown the dust of my 1971 and 1972 issues and here is what I found in Notes & Errata:

May 71: The capacitor across the 4.7K second mixer source resistor shown as 0.1μF, should read 0.01uF.

June 71: The layout diagram of the first oscillator on page 81 shows the two 0.01 capacitors as ceramic types. The correct capacitors to use here are the 0.01μF 160V polyester type. Four of these capacitors are indicated in the parts list, the others being located in the base circuit of TR12 and connected from pin 3 of L6 to ground.

1972: No reference to this project found in notes and errata.

There may be further references in later years but I didn't dig deeper at this stage.

Ta GTC. I spotted the error on the RF diagram while I was making the RF strip. I presume the 0.01μF 160V listed are meant to be Philips mustard tubular, because one of these is visible in the close up photo of L6. I've got some, but they'd be a very tight fit on the first oscillator board; 0.01μF 100V greencap polyesters would be better. Would using those make any difference to the oscillator?

I've got EA complete from 1973 to 1976, so I'll check through the errata there.

There are so many 'poly' type caps around these days that I cannot keep up with them.

I'm guessing that EA was saying that ceramic is not suitable in those positions. And I don't know why they specified 160V caps for that application.

Maybe try greencaps and see how you go.

EA normally used the Philips mustards in the prototypes of their projects in those days, and I think 160V was the lowest voltage the Philips came in. The Elna greencap polys were much smaller, but they were fairly new, not made in Australia, and perhaps not trusted by the designers. I don't know if greencaps are different in construction or worse for RF; I'll give them a try as you suggest.