The instruction manual is available on the American QRP Web Site as a free 2.4mb PDF file
down so you can review it before ordering so I will not go into it here.
Top an bottom views of a real pretty PCB
All the resistors were installed one at a time. Each resistors was measured with a
DVM to ensure correct value BEFORE installation and the solder joints were checked
before clipping the leads. Also note that you can read the color codes L to R and
top to bottom making it easier to trouble shoot
All the transistors have been istalled, again one at a time.
Checking joints before clipping the leads.
All capacitors have been installed, one at a time.
Checking joints before clipping the leads
T1 and L1 have been installed. Hardest part is counting the turns on the cores[g].
Now that all the through the hole components have been installed it is time to clean
the underside of the PCB to remove residue. the white specks are from the scanner
and are not on the PCB.
The final construction is primarily putting the case together and alignment of the
receiver coil "L1". This process is covered very well in the supplied manual and I was
totally suprised at the ease my "TIN EAR" came together. When the battery was hooked
up and it was turned on "CW" tones greeted my ears. Alignment of the coil also was a
snap to accomplish.
My next step after allowing the epoxy to cure over night is to hook up a
Tuna Tin 2 to it (the instructions are there also) and see it we can get a contact
Total time from start to finish was 7 hours.
My Hat's off to Wayne McFEE NB6M for a nice Job on a good product.
NOTE! I've shortened the brass 6-32 tuning screw to a length of 3.5cm decreasing the
tunable range of the VFO from 400khz to 125 khz. The range is now from 6.990mhz to 7.09 mhz.
Making it better for the CW portion of the 40m band.
Now to carry it one step further. I have taken the last Tuna Tin II that I built several years ago checked it out with the
Tin Ear and it seems like the two of them are compatable. Neat Idea, HUH [g].
Using 2N2222a's as Q1 & Q2 and a 7.040 mhz crystal with 12.98vdc battery the Tuna Tin draws 67ma key down for a
WHOPPING 867mw ( I think I got the math right). ought to be fun on straight key night..
A testemonial from WA5BDU
"Nick Kennedy" WA5BDU
A Tin Ear Tale
Date: Monday, April 19, 2004 1:11 PM
Just finished my tin ear receiver so here are some impressions.
First a quick look at the schematic and Ö I didn't see anything. I'm
not one of those guys who can just glance at a schematic and then
understand the radio. So some closer scrutiny is in order. No ICs. So
it's a purist rig, like a 2N2/40 but less complex, like a tuna-tin, but
more complicated. It occurs to me that in the 60's, the ad on the box
would have described it as an "8 transistor radio". So eight transistors
and no NE602 and no LM386. Can this thing really work?
It's full of interesting quirks that take a different road from the ones
in the standard QRP community cookbook. The first thing that stands out
is the permeability tuned VFO. Pretty sure I've never built one before,
probably because I didn't know that such a simple design could work this
well. Other than being cool, its nice feature is to give multi-turn
tuning without resort to VCOs and 10 turn pots, or capacitors with
reduction drives. Wayne noted that brass gives a *reduction* in
inductance, so tuning is clockwise "up", as is normally expected. So
you gotta ask, why does the brass slug reduce inductance? I think it's
a different phenomenon than a typical iron or ferrite slug, which
contains magnetic particles that can align with the field. In this
case, currents induced into the brass create fields that oppose the
field caused by the coil thereby reducing the inductance. Is that
right? The VFO doesn't have (or need) any buffer, it connects right to
the mixer port, which being a JFET gate, doesn't require any driving
The mixer (product detector) is unusual too. Kind of like a dual gate
MOSFET mixer, only in this case, two JFETS are connected in cascode
(series). The LO goes to one gate and the RF from the antenna goes to
the other. The manual credited EMRFD for ideas for this receiver. Both
the mixer and the audio amplifier are described in that book. EMRFD
says this mixer has some gain, so there's more advantage over a passive
mixer than just being unusual.
Following the detector is a single transistor amplifier configured for
high gain. It's a really simple circuit with just two transistors, on
in the collector lead and one from collector to base. It has some
drawbacks in controllability of gain and maybe frequency response, but
is ideal for this application. I've seen similar things as frequency
counter front ends, microphone preamps, and I think in NA5N's regen
receiver of a few years ago, as a preamplifier.
Finally is an audio output section which EMRFD describes as being
roughly an LM386 built with discrete parts. So you might call it a
disintegrated circuit. I spent some time trying to figure this one out.
I think I finally understood the "floating voltage source" thing (Q6),
but the overall gain and DC biasing escapes me so far. Jeff Furman?
There are kits from "bag-o-parts" to precision engineered radios. This
one fits into the latter category. The manual and overall design and
packaging remind me of Heathkit. I built the board in my own sequence
(audio amp, mixer, VFO), and then went to the manual for the tricky
assembly stuff. My first (and maybe only) issue was with the famous
California Burger straw. I couldn't find it. Did they leave it out?
Did it get pitched as trash? Or is it lost in the vast expanse of
detritus on my work table? Anyway, I dug out a replacement straw from
the kitchen. Same sporty red stripes, but will a low-Q Arkansas Sonic
straw function the same electrically? It seemed to do OK when I
soldered it in and energized the board, but when I got to the part where
you mount the thing, I discover that my replacement straw is way too
small in diameter. They must really gulp down Coke in California! So
now what? Do I order one from Mouser? Hope a plane to California?
First, I decided to root through my collection of sleeving and heat
shrink tubing. Finally found a piece that's a nice fit for the PEM nut
(whatever that is) and brass thingy and proceeded to rewind the coil.
After assembly, I check my tuning range and it's 7160 to 7675 kHz. Holy
cow! I'll never get that much adjustment by compressing turns. But I
did. Bunched 'em up good and got down to 6915 to 7395 kHz. Just about
perfect. (I'm not keen on broadcasters in the area anyway--most of them
spend way too much time denouncing the religion I was brought up in, and
many other religions too, for good measure. I'd rather copy tbe Bible
broadcasts on 7041.)
Everything goes together just fine; the little case is a beauty, rugged and tiny.
BTW--having the manual on a little-bitty CD rom was a nice touch. You
can also get the manual from the AmQRP site. Only one thing I didn't
like about it was that the schematic was kind of fuzzy. Like a lot of
PDF drawings I've seen, it prints out that way and component designators
and values are hard to read on the print-out. I kept having to go back
to the screen, which was marginally easier to read.
As predicted in the manual, I got motorboating when I used a cheap
"heavy duty" 9 volt battery, but it went away when I put in a good
alkaline unit. An NiMh rechargeable out to be good, because they are
high on the voltage scale. One guy on the web said a big capacitor
across the power terminals would help with motorboating. I'll have to
try that and see if it allows me to use the cheap batteries. I didn't
hear any of the hum mentioned as a possibility in the manual, even using
my "big" 40 meter antenna.
For the first few minutes after turn-on, the radio drifts a bunch. Then
it settles down and becomes pretty stable. I guess it's the battery
deciding where its voltages is going to sit under load.
I like the sound. There's no explicit filtering--just roll off from the
selection of capacitor sizes and maybe a couple RC networks. I haven't
tried to listen to much AM or SSB, but CW sounds nice. I developed
pretty good noggin DSP filtering in my younger days.
I'd guess that the sensitivity is not up there with receivers designed
with that in mind. I haven't done any tests, but I'm copying what I'd
consider moderate to strong signals just fine.
On the Air?
Could you use this for actual communications? Well, I'd have gladly
traded my first two or three receivers I used in my teenage years for
this one. It does seem like making a QSO is a necessary initiation for
a new piece of equipment, even if itís a receiver. So I got on
somewhere around 7025 with my 2N2/40 as a TX this morning and called a
few CQs. Eventually, AK4G in Huntsville, AL came back and we had a
short QSO. Copy was fine on the Tin Ear.
There. Another adventure in the books.