[Premium-Rx] ITT Mackay 3021

[Thomas Adams]

Greetings, All.

Of late I've been so busy playing with my Racal equipment that I
haven't done much with the other gear in my shack. Last night I
changed that pattern, and for the first time in months fired up the
Mackay 3021. The experience reminded me of a few things that
have bothered me with the rig, which I've been meaning to talk
about here for some time.

First off...   I suppose I've been spoiled by Racals; I find myself
using Racal performance as the standard by which all other HF
receivers are compared. Perhaps that's unfair, but that's the way
it is. It takes a damned fine receiver to compare favorably to most
Racal products!

As far as the Mackay 3021 is concerned, I have a question for the 
other owners of Mackay receivers on the list.

As long as I've owned the 3021 I've been badly dissapointed by 
it's strong signal handling characteristics, especially on the AM
broadcat band and below. At this point I'm not sure if I have some
problem with this particular radio, or if there are design proplems
with the front ends of the entire series.

According to the QST product review on it, they too had some rather
serious questions about intermod in the front end. They attribute 
them to the RF clipper circuit in the preselector, intended to protect
the RF amp (Q1, type CP632). The QST reveiw claims that strong
signals drive the clipper (a pair of 1N4001 power supply diodes!)
into nonlinearity, thus generating intermod. Incidentally, they too
had problems with local AM broadcasters in this respect.

Let me point out that my location is about a half mile from a 5 KW
AM broadcaster (I can see the tower tops from my back yard), which
is thankfully daytime only. When any other receiver in the shack (and 
there are PLENTY of them here!) is connected to my 160 metre Windom 
they ALL handle the signal levels fine,  except for the the hi - Z input of

my R-392, which gets sort of muddy. However, the 3021 becomes 
totally useless thru it's entire tuning range.

During the day, the AM broadcast band is a horrorshow here. The 10 DB
attenuator is MANDATORY, and the RF preselector becomes a serious
problem; local AM signals, peaked by the preselector, actually cause a
bit of feedback! The preselector has to be critically detuned to lower the
signal levels slightly in order to eliminate said feedback.

I've long considered building a band stop filter for the rig, covering the
AM
broadcast band, or at least putting in a suck out trap to knock down the
nearby AM station's level some...  just haven't gotten around to it (the
project list here is a mile long).

Is anyone else out there having similar problems with the 3021 front end?
If not, it looks like I'll have to tear into the preselector to look for
something
fried.


A hint to other 3021 owners...

When I got mine, someone had replaced a bad synth memory battery (on 
the back of the front panel, above the S meter) with three AAA nicads. Not 
a good move.

The charger circuit in the rig is pretty much guaranteed to destroy nicads
in
a BIG hurry; no current limiting. When I got the rig, the nicads were baked
to
the point of leakage. It appears that the original battery is a lead acid
type.
Unfortunately, exact replacements for the original don't appear to be
around.

A far better solution, tho not perfect...  I added a small 6 volt gel cell
(Panasonic
LCR6V1.3P) to replace the stock memory floater. Naturally, it won't fit in
the
same space as the original battery, so I extended the leads and routed them

to the only space available; between the left side wall of the rig and the
power
transformer. The transformer is, of course, a heat producer (BAD!), but it
seems
to not get that hot. The battery life has been 3 years so far, and I've yet
to see
any conditions where the transformer gets hot enough to seriously degrade
the
gel cell; it's 10 - 15 degrees above ambient and not much more, even after
all
night long wave DXing sessions. 


The Mackay 3000 series receivers are interesting, but we have to bear a few
things in mind with them.

These are early 1970s designs! If we're to take Osterman's book as gospel,
these are Mackay's FIRST GENERATION of solid state designs. I can remember 
some of the solid state stuff from other makers at that time...   the ham
stuff 
was atrocious! Unless you were wiling to pay huge amounts for commercial
rigs like the 3000 series (Osterman claims $4200 - $6000 for the 3021, and
the contemporary HRO-500 went for $1300 - $1995), you just weren't going
to find a decent solid state receiver. RF semiconductors and receiver
design
techniques for them were still in thier infancy, even tho they grew up
FAST...
five years saw quantum leaps in receiver performance.


Anyway...   you Mackay owners out there...   how's your front end
performance?



73's,


Tom, W9LBB
Owner & Operator of the
Mahon Loomis Memorial Monitoring Station
& Irish Setter Retirement Home
Sun Prairie, Wisconsin