[VE7SL] Drake 2NT And The Novice Rig Roundup (NRR)

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VE7SL - Steve - Amateur Radio Blog

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Drake 2NT And The Novice Rig Roundup (NRR)

Posted: 12 Sep 2017 09:04 AM PDT
http://ve7sl.blogspot.com/2017/09/drake-2nt-and-novice-rig-roundup-nrr.html


One of this summer's radio workbench projects was to refurbish my Drake
2NT transmitter for this winter's NRR event. The 2NT was introduced in
1966 with the 'novice' ticket-holder in mind, selling for $129. It was the
first and only CW-only transmitter produced by R.L. Drake.


As novice transmitters go, the 2NT was a cut above some of the others out
there, boasting interesting features such as a built-in antenna changeover
relay, sidetone oscillator, grid-block keying and built-in low pass filter.


The tune-up procedure was simplified as well and with Drake's reputation
for quality construction, the 2NT became a popular choice for Novices and
Generals alike.





My own 2NT was purchased, along with the matching 2C receiver and
speaker/Q-multiplier combo over 25 years ago at a Washington state ham
fleamarket. Ever since then they have been patiently sitting on the shelf,
trying to catch my attention.

The motivation and much-deserved attention finally arrived this year after
enjoying last winter's NRR and hearing several great-sounding 2NT's on 80,
40 and 15m CW. I operated the week-long Roundup with my
homebrew 'Longfeller' at 5W output, in order to qualify for the QRP
category.

6AG7 - 6V6 'Longfeller'I have to admit, the Novice Rig Roundup, was one of
the most enjoyable contests I have entered in many years! Hearing many rigs
from the 50's and 60's sounding so good was just a bonus. It was
particularly gratifying to be able to work the midweek daytime activity on
15m ... a luxury that we may not enjoy now for several years if most of the
long term solar forecasts are correct.

I eventually ended up with 68 contacts, but at 5W, it was a challenge ...
most of my many 'CQ NRR' offerings were unanswered, so it was mostly
a 'search and pounce' operation. With this in mind, I soon decided that
next time, I'll get the 2NT ready to go and hopefully, with a little more
oomph, can attract some callers.

Each entrant received an NRR certificate - a nice touch
Rather than hunt down and purchase the individual replacement
electrolytics, especially the multi-unit can capacitor which was
impossible to source, I ordered the '2NT re-cap kit' from Hayseed
Electronics. They supply replacement kits for several boatanchors and are
able to make and stuff multi-section can capacitors to match the original
size and specs ... and all at affordable prices.

After cleaning the chassis and all of the switches, re-tubing with new
tubes and removing / replacing all of the electrolytics, the 2NT was ready
to go. Using a crystal for excitation, the following results were obtained:

80m 103W input 75W output efficiency = 73%
40m 92W input 65W output efficiency = 71%
20m 92W input 65W output efficiency = 71%
15m 92W input 55W output efficiency = 58%
10m 92W input 50W output efficiency = 54%

Keydown voltages averaged ~520V while plate current ranged from 170-200ma.
All-in-all, right on target and not bad for a 51 year old transmitter!

The 6EA8 modified Pierce oscillator in the 2NT seems
particularly 'crystal-friendly', as every old style FT-243 style crystal
that I tried sounded great. Even the newer ones from AF4K using a modern
HC-49 crystal slab mounted inside a vintage FT-243 holder sounded great and
worked perfectly.

My newly refurbished 2NT - ready to go
A couple of days later, I returned to the bench to take some blog photos
of the rig delivering power into the wattmeter. When I turned the 'stby'
switch to 'transmit', the plate current suddenly shot up (with no keying)
and the meter on my Variac supply indicated over an amp being drawn by the
power transformer ... all with zero output and no crystal plugged-in!

A look at the schematic diagram revealed that with the grid-block keying
system, the final amplifier's cathode is always grounded and a low voltage
negative bias applied to the grid keeps the plate current cut-off until
being keyed ... with cut-off bias missing, plate current will soar, along
with transformer primary current. I suspected that something had gone
haywire with the bias supply.


A quick check of the 2NT's printed circuit board containing the bias
system components among others, indicated a discolored silicon rectifier
(D5) in the bias supply. An in-circuit measurement revealed that it was
indeed shorted, basically supplying raw AC across the filter capacitor and
shorting out the transformer winding, quickly elevating the transformer's
temperature in the bargain ... not good.

Although the diode only has to handle a small amount of current, it was
mounted with a heat-producing 2W resistor straddling its top surface. As
well, the phenolic circuit board was noticeably discoloured from the heat.
I suspect this was the main reason that D5 eventually failed.

My 2NT was an early one, serial #670, so perhaps this parts-arrangement
was re-engineered in later models. Once the diode was replaced with a much
smaller modern one, of twice the rating, everything returned to normal.
The last thing I would want to do at this stage is to burn out the
transmitter's unique power transformer, undoubtedly impossible to replace
nowadays.

The next bench project will be to refurbish and improve the stability of my
Heathkit VF-1 VFO and to mate it with the 2NT.

'55 QST VF-1 adThere are several things that can be done to a stock VF-1 to
improve its performance. Its wonderful backlit green dial will bring back a
lot of memories from my teenage operating days with the VF-1 ... most, but
not all of them, warm and fuzzy.



Another small quirk noticed on my 2NT is the meter mount. My early model
has the meter mounted so low that the silk-screened 'PLATE CURRENT MA.'
label is not clearly visible when looking straight-on.

My #670Later models show that this was changed by moving the meter a
little higher so that the label can be easily seen without having to look
down inside. Nothing major, but something apparently missed during the
initial panel design.

Later modelsI'll have more to say about the 2018 NRR later, but if it's
something that you may be interested in trying and you don't yet have a
suitable novice-style rig, it's not too late to start looking, building or
refurbishing.

You can read many interesting soapbox comments and see some nice NRR
station photos from the previous two events here and here, but read with
caution as you could easily get hooked. I find pages like this very
inspiring and they remind me of the days when QST would publish photos,
soapbox comments and exacting equipment descriptions used by each section
winner in the annual November Sweepstakes contest.

Winner's gear in '55 CW SS - remember these?NRR activity really skyrocketed
last winter and I expect that it will be an even busier event next time.
There are several CW contests that I'm looking forward to this winter and
the NRR is right near the top of the list. I hope to see many of you in the
2018 NRR!