# 4 2017 Vol-23

April 9th NMRCC Meeting Theme: Code keys, bugs, sounders

By 1946, National had quickly returned the band spread option to the NC-240 and added the suffix "D" to distinguish that this receiver was the latest version. The 200kc to 400kc band was replaced with AM BC band coverage. National also added pedestal-type feet to the receiver cabinet and to the speaker cabinet. http://www.radioblvd.com/NC100.htm

The National NC-2-40D Communications Radio by Richard Majestic

The National NC-2-40D is a single conversion general coverage shortwave receiver that tunes: 0.48-1.04, .92-2.1, 1.68-4.05, 3.4-4.05, 3.4-7.4, 6.9-7.35, 6.65-14.6, 13.8-14.46, 13.9-31 and 26.9-30.05 MHz. Features include: ź" head-phone jack, S-Meter, antenna trimmer, RF Gain control, dial lamp, phono input, circular logging scale, noise limiter, mute, tone control and hinged top cover. Five selectable bandwidths: 6,

4, 2, 1, 0.2 kHz. 19.25 x 10.675 x 15.5 inches. This radio does not have a built-in speaker. The suggested optional speaker is the NC-2TS. From: Universal Radio Inc. The NC-2-40D is a professional communications receiver in every sense. Sturdy and dependable, it uses a cast aluminum coil set carriage for all tuned stages and a positive drive mechanism. All

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Auction item 1926 Kol-ster TRF radio

Old radio tube boxes with NOS tubes, Richard Majestic discusses

Coming soon

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The NMRCC March 12th, 2017 Meeting

Our meeting program speaker was Mike Langner retired chief engineer of KOB group of radio stations in Albuquerque NM. Mike talked about the history of radio with a great set of slides with old radio clips and old television show blocks. The Meeting theme was old and interesting tube boxes and old radio books. See the pictures on page 3. As you can see we need a Secretary, it’s not in my pay grade.

Kids today don't know how easy they have it. When I was young, I had to walk 9 feet through shag carpet to change the TV channel.

NMRCC Officers for 2017

• David Wilson: President

• Mark Toppo: Vice President

• Richard Majestic: Treasurer

• open Secretary

• open Membership

• Ron Monty Director

• Ray Truijillo Director

• John Anthes Director

• John Hannahs

• Richard Majestic: Newsletter Editor (President pro-tem)

NMRCC 2017 MEETINGS April 9th Code keys, bugs, sounders May 21st Spring Picnic (TBA) June 11th Field Trip ABQ Bal-loon Museum, plus Presentation on Stratosphere radios and histo-ry July 9th Early plastic, Catalan and Bakelite radios August 13th Radio repair work-shop September 10th Unusual devic-es to stump the experts October 8th Fall Picnic (Wilson’s) Field Trip to Goddard Hall-Klipsch NMSU November 12th Little known radio manufacturers December 10th Holiday party (Toppo’s)

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Some of the old tubes owned by Richard Majestic and radio history books from Chuck Burch’s library

Above was NOT part of the Auction

In the monthly auction was a Kolster TRF radio and matching speaker, donated by Shannon Laury from the late Tom Laury’s radio col-lection. Thank you Shannon. A B&K 1471B oscilloscope.

NMRCC Auction Lite

- Logic is a systematic method of coming to the wrong conclusion with confidence. - Whenever a system becomes completely defined, some damn fool discovers something which either abolishes the system or expands it beyond recognition. - Technology is dominated by those who manage what they do not understand.

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Sparton 558 Sled

coils are on polystyrene forms with air trimmers used throughout. It is truly stable and selective. Designed for the radio ama-teur, the NC-240D receiver is also suitable for general com-munications service in the 490 to 30,000 kc. range. Cali-brated electrical band spread tuning is provided for the 80, 40, 20, 11-10 meter Amateur bands.

FEATURES: · Full vision, easy to read, cali-brated dial · 6 general coverage and 4 band spread dial scales · Single tuning and band switch-ing control knob · Stable high frequency oscillator circuit · Flexible crystal filter · Series valve noise limiter · Auxiliary numerical logging dial

A.V.C. CHARACTERIS-TIC: Constant within +-3 db. from 10. to 100,000 micro-volts input. IMAGE REJETION: Above

(Continued from page One) 50 db. up to 10 Mc. Above 40 db. up to 15 Mc. Above 30 db. up to 30 Mc. AUDIO FIDELITY: The fre-quency response of the audio system is flat within +- 2 dB. from 50 cycles to 10,000 cy-cles. POWER: Approximately 70 watts; either 110-120 or 220-240 volts 50/60 cycle, Phase AC, A plug and socket is pro-

vided for convenient external connection for battery opera-tion. POWER OUTPUT: A 10,000 ohm output circuit delivers 8 watts with negligible distortion. PHYSICAL DATA: Table Model: NC-240DT; 19 1/4" x 10 5/8" x 15 1/2": Weight- 60 Lbs., Finish -- Gray Wrinkle; Enclosure -- Cabinet. Rack Model: NC-240DR; 19" x 10 1/2" x 17 1/2"; Weight- 65 Lbs.; depth behind pan-

el 14 7/8" overall; Finish -- Gray Wrinkle; Enclosure -- Dust Cov-er. PRICES: Rack or Table Mod-el (with tubes) Net $225.00 NC-2RS (Rack) or NC-2TS (Table) Speaker Net $16.44 Source: National Radio Products 1948 Catalog Restoration Details Okay, with the general specs out of the way, let’s dig into this great radio. When I received this radio from my friend and fellow club member for electronic resto-

ration it was easy to see it had been owned by a ‘ham’ and had been repaired, modified and generally destroyed over the years. The local oscillator (LO) tube had been changed and the circuit modified, the mixer tube had been changed and the circuit modified, the IF amplifier circuit had the origi-nal 6K7 tubes but the circuit modified, the B+ build-out resistors values changed, cath-ode resistors changed, there were resistors across the pri-mary of the IF transformer tanks however, the ‘ham’ to-tally missed why the radio did-n’t perform well, the IF stage screen voltage dropping resis-tor measured about 1Meg but it was marked 22,000 Ohms

and on the schematic it was 22,000 Ohm 1 Watt resistor. Even the power supply had been modified; different electrolyt-ics, some oil bath foil capacitors in par-allel, resistor values changed, the LO voltage regulator tube was the wrong voltage. One fortunate thing the ham missed changing was the audio circuits, I guess it was too hard to get at because of

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the band switching coil assemble was in the way even when at its max clearance position.

The band switching coil assemble is a mechanical work of art; the coils and their associated air trimmer ca-pacitors are in individual cast shield boxes, cast from one large aluminum casting. The coils and air trimmer switch contacts stick through the top

of the casting to connect to the sta-tionary contacts that are connected to the tuning capacitor and appropriate LO and RF amplifier stages. Coils and air trimmers for the antenna in-put circuit, the RF amplifier plate circuit and the local oscillator are

wound on a plastic casting too, that are designed to prevent the tuned circuits from drifting in value as the receiver changes temperature. The engineering

is nothing short of superior. The bottom of this cast aluminum housing is covered with a flat aluminum sheet with access holes for the air trim-mer adjustments. The entire block of alu-minum that houses the coils and trim-mers slides left to right on lubricated rods driven by a pi-non gear and a rack which is part of the cast aluminum coil housing.

I started this restoration project like no other I had done before, I removed eve-ry electrolytic, every capacitor, re-moved every resistor, including a few wire wound resistors and removed all non-original wiring. I cleaned up all

the tube socket ter-minals and other ter-minal boards. I then started building an original National NC-2-40D radio, start-ing with the power supply moving to the antenna terminals, which also had to be replaced since the

radio originally had a high impedance (400 Ohms) balanced antenna input circuit and the ‘ham’ had soldered an unbalanced PL259 52 ohm coax con-nector in its place. No resistor to termi-nate the 52 ohm coax, no Balum trans-former either; so much for engineering

knowledge. I used the original style lacquer covered linen and plastic sol-id copper color cod-ed wire to rewire the radio. Since I didn’t have any of the origi-nal paper covered foil capacitors I used the Chinese best My-lar foil capacitors. I found and purchased the original value can

electrolytics. I used only the original value metalized resistors. The original BFO (beat frequency oscil-lator) tuned oscillator tank was in a alu-minum box on top of the chassis, it had also been modified mechanically and electrically. It took some effort to re-move cobbled and glued parts that con-nected the BFO tuning shaft to the non-original variable capacitor and replace it with original value and style parts. Again, the ‘ham’ redesigned the BFO and didn’t look at what caused the BFO oscillator drift; the resistor values had changed. I took apart all the IF transformers and checked the parts and performance, they had not been modified or destroyed. The NC-2-40D is a single conversion super-heterodyne receiver, there are only two IF amplifiers, the first tuned circuit is a 455kHz. Parallel tuned tank with crys-tals to decrease or increase the band-pass width, followed by two additional typi-cal dual 455kHz. tanks, mutually cou-pled, in the next two IF transformers. The second detector is unusual for a AM detector, it uses a triode (6SL7) B+ on the plate, grid to the third IF transformer output and the cathode has the detected RF envelope amplitude signal. This de-tector is very linear and lowers the audio distortion measurable. The only other radio I’ve run into using this detector was a McMurdo Silver 15-17 and it measured under 0.5% THD, most other radios are typically 3-5% THD just be-cause of the detector. Performance and Features You probably noticed that the NC-2-40D does not have a typical band spread con-trol, it doesn’t need one because it has separate bands for 10, 20, 40 and 80 me-ter ham bands. The air trimmer capaci-tors and plastic coil formers make this radio very stable and drift free on all bands. In my testing using HP 606A is was almost drift free after a few minutes of warmup, as tested with a frequency counter. The National after a few minutes only drifted a few cycles after an hour of testing. The sensitivity as tested remains con-stant at better than 1 microvolt, with 20dB S/N on all bands and from one end to end of each band. I didn’t bother to sweep the radio but would guess it has a constant bandwidth from 10uV to 1mV of RF sensitivity since the AVC voltage

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begins to rise at 10uV. The noise limiter is the typical compres-sor circuit that minimizes impulse noise. The audio circuits are designed for wide bandwidth and the output circuit uses push-pull 6V6s driven with a electronic phase splitter. The matching National speaker, the NC-2TS contains the output transformer and a large speaker. When I connected a better output transformer and speaker the sound quality was very good with frequencies above 4kHz. As meas-ured. The radio is very quiet considering the high sensitivity and this makes for a happy user. Maybe two or three conversion commu-

nication receivers are better in sensitiv-ity and/or selectivity but overall this National might just be the best single conversion communications receiver ever produced. It’s only limitations are the simple pointer style dial and it’s a true boat-anchor, it is very heavy, over 50+ pounds. `Richard Majestic

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The New Mexico Radio Collectors Club is a non-profit organization founded in 1994 in order to enhance the enjoyment of collecting and preservation of radios for all its members.

NMRCC meets the second Sunday of the month at The Quelab at 680 Haines Ave NW , Albuquerque NM Tailgate sale at 1:00PM meetings start at 2:00 pm. Visitors Always Welcomed.

NMRCC NEWSLETTER

THIS PUBLICATION IS THE MONTHLY NEWSLETTER OF THE NEW

MEXICO RADIO COLLECTORS CLUB. INPUT FROM ALL MEMBERS ARE SOLICITED AND WELCOME ON 20TH OF THE PRECEDING

MONTH. RICHARD MAJESTIC PRO-TEMP NEWSLETTER EDITOR, SEND ALL SUBMISSIONS IN WORD FORMAT, PICTURES IN *.JPG

FORMAT TO: RMAJESTIC@MSN.COM

N E W M E X I C O R A D I O

C O L L E C T O R S C L U B

New Mexico Radio Collectors Club Richard Majestic (Membership inquiries)

5460 Superstition Drive Las Cruces NM 88011

E-Mail: ronmonty@comcast.net Phone: 505 281-5067

E-Mail: rmajestic@msn.com Phone: 575 521-0018

FOR INFORMATION CHECK THE INTERNET

http://www.newmexicoradiocollectorsclub.com/

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