[CW] Mackay 3010B tube receiver

Sun Sep 15 21:13:26 EDT 2019

I have a Mackay 3010B that Quincy Electronics gave to me in hopes of
selling it.

Info here:  http://www.w1vd.com/Mackay%203010B.html

*Mackay 3010B*

*Front end attenuator OFF:*

*Band* *MDS* *Blocking* *Two-tone D.R.*

*(20 kHz)* *(20 kHz)*

80 meters -146 dBm   93 dB 68 dB
40 meters -141 dBm   96 dB 67 dB
20 meters -140 dBm 102 dB 68 dB

*Front end attenuator ON 1st position:*

*Band* *MDS* *Blocking* *Two-tone D.R.*

*(20 kHz)* *(20 kHz)*

80 meters -135 dBm   94 dB 66 dB
40 meters -128 dBm   98 dB 69 dB
20 meters -126 dBm 103 dB 69 dB

*AM Audio S/N:* 43 dB

*AM Audio Frequency Response: *

*100 Hz* *200 Hz* *400 Hz* *600 Hz* *800 Hz* *1 kHz* *2 kHz* *3 kHz* *4 kHz* *5
kHz* *6 kHz*

-4 dB +1 dB 0 dB +2dB +2 dB 0 dB -2 dB -10 dB -24 dB -40 dB -

*AM Audio Distortion: *

*Mod%* *100 Hz* *200 Hz* *400 Hz* *600 Hz* *800 Hz* *1 kHz* *2 kHz*

30% 13% 8.9% 7.1% 6.3% 5.6% 4.5% 4.0%
50% 13% 7.9% 6.3% 6.3% 6.3% 6.3% 7.9%
70% 20% 13% 11% 10% 7.1% 6.3% 7.1%
90% 32% 22% 16% 14% 11% 7.9% 7.9%
100% 40% 25% 18% 16% 13% 8.9% 8.9%

*Notes:* This receiver is pretty uncommon so a few comments are in order.
With 0 dB front end attenuation and maximum i-f gain this receiver has
extraordinary gain and sensitivity - especially at the lower frequencies.
Designed mainly as a shipboard receiver it is likely this receiver would
have performed well on 500 kHz with the ships antenna fully encrusted in
ice and laying on the deck! Words can not adequately describe the unbridled
gain of this receiver - you'll just have to try one for yourself.

The receiver is extremely well built on a cast aluminum foundation in which
individual stages occupy their own compartments. DC and bias voltages enter
through feedthrough capacitors and signal openings from compartment to
compartment are kept as small as possible. One wishes all receivers were
built this way!

Unfortunately, the blocking and two-tone dynamic range numbers tested
disappointingly low - even with the i-f gain of the receiver cut way way
back. Considerable time was spent to insure that the receiver was
functioning, as best as one can tell, to factory specifications. All
voltages were correct, as was LO injection levels when compared with the
figures given in the manual. The rf circuitry used is somewhat
unconventional. The receiver covers from 70 kHz to 30 MHz and uses up
conversion to a first i-f of 38 MHz. The main signal path includes a
manually switched front end attenuator, manually switched front end
bandpass filters that feeds a single stage 7788 tube rf amplifier. Signal
from the plate of the rf amplifier passes through a 14 section 30 Mhz low
pass filter. This is applied to a 6C4 cathode follower that feeds the first
mixer - a quad of 1N82A 'VHF' diodes in a balanced design. The signal is
amplified and filtered by two tuned circuits, a single 6688 amplifier tube
and two more tuned circuits. A 6BL8 triode section forms another cathode
follower which feeds the grid of the 6BL8 pentode section as the 2nd mixer
with an output at 5.94 MHz. A somewhat unusual arrangement has the LO
injection in series with the rf signal to the grid. The plate of the 2nd
mixer passes through a 6 kHz wide crystal lattice filter. From there it's
on to the third mixer - a 6BE6 converter stage - for the final i-f of 455
kHz. Here, the signal encounters the Collins mechanical filters for either
SSB or CW. No additional filter is used here for AM - just the 6 kHz filter
in the previous i-f. The remainder of the circuitry is pretty
straightforward. One nice feature of this receiver is that it does have a
product detector.

This receiver was on loan so it was only possible to observe its
performance - not modify the receiver to try to improve it. In order to
locate the source of the poor dynamic range a high impedance probe /
spectrum analyzer setup was used to 'sniff' IMD stage by stage. The culprit
turned out to be the 6BL8 second mixer stage. With simple tests and limited
time I was unable to determine the exact cause of the poor IMD performance
but would suspect the 6BL8 biasing, or more likely the crystal filter in
the plate circuit or the VFO amplifier which has it's output in series with
the rf signal. Even if the IMD could be improved in the second mixer, next
in line is the third mixer - a 6BE6 converter - generally a dynamic range
'show stopper' in receivers where it's used. This would be one fun receiver
to modify for truly high performance!

The AM distortion numbers show the somewhat typical increase at lower audio
frequencies - most often caused by the low audio frequencies riding on the
AGC line. Also there is the usual increase in audio distortion as the
modulation percentage increases. This is due to the detector's inability to
cleanly demodulate the higher amplitude levels although this receiver does
pretty well.

It probably works but there is no schematic and there is no power plug.
The power plug it appears is like a vacuum tube octal plug.  It has no
outer cabinet, it's rackmount.

Obviously there are other connections there as well.

I'd have to crate it - either in wood or cardboard.

Then mail it - it's heavy.

You have to either pick it up in Marshfield, MA or have me pack it and post
it.

Cardboard is cheaper but I know a carpenter who can make a box as long as
the box keeps the package under 70 pounds, it's good to go.

Inside the crate will be anti-vibration materials.

You're paying for all of this if you want me to post it.

Or you can pick it up where I live.  Free no extra cost..

Make a reasonable donation $100 or more and agree to pay the shipping cost
and it's yours.

73

DR
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