Auction item 1926 Kolster TRF radio # 4 Vol-23 2017 Old radio tube boxes with NOS tubes, Richard Majestic discusses Coming soon 2A3 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" headphone 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 (Continued on page Four)
The NMRCC March 12th, 2017 Meeting NMRCC 2017 MEETINGS 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. April 9th Code keys, bugs, sounders May 21st Spring Picnic (TBA) June 11th Field Trip ABQ Balloon Museum, plus Presentation on Stratosphere radios and history July 9th Early plastic, Catalan and Bakelite radios August 13th Radio repair workshop September 10th Unusual devices 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) 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) Two
NMRCC Auction Lite 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 collection. Thank you Shannon. A B&K 1471B oscilloscope. Some of the old tubes owned by Richard Majestic and radio history books from Chuck Burch s library - 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. Three
(Continued from page One) 50 db. up to 10 Mc. Above 40 coils are on polystyrene forms db. up to 15 Mc. Above 30 db. with air trimmers used up to 30 Mc. throughout. It is truly stable and selective. AUDIO FIDELITY: The frequency response of the audio Designed for the radio amateur, the NC-240D receiver is system is flat within +- 2 db. also suitable for general communications service in the cles. from 50 cycles to 10,000 cy- 490 to 30,000 kc. range. Calibrated electrical band spread POWER: Approximately 70 tuning is provided for the 80, watts; either 110-120 or 220-40, 20, 11-10 meter Amateur 240 volts 50/60 cycle, Phase bands. AC, A plug and socket is pro- FEATURES: Full vision, easy to read, calibrated dial 6 general coverage and 4 band spread dial scales Single tuning and band switching 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 microvolts input. IMAGE REJETION: Above vided for convenient external connection for battery operation. 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 panel 14 7/8" overall; Finish -- Gray Wrinkle; Enclosure -- Dust Cover. PRICES: Rack or Table Model (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 restoration 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 original 6K7 tubes but the circuit modified, the B+ build-out resistors values changed, cathode resistors changed, there were resistors across the primary of the IF transformer tanks however, the ham totally missed why the radio didn t perform well, the IF stage screen voltage dropping resistor 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 electrolytics, some oil bath foil capacitors in parallel, 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 Sparton 558 Sled Four
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 capacitors 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 stationary contacts that are connected to the tuning capacitor and appropriate LO and RF amplifier stages. Coils and air trimmers for the antenna input 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 trimmer adjustments. The entire block of aluminum that houses the coils and trimmers slides left to right on lubricated rods driven by a pinon 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 every electrolytic, every capacitor, removed every resistor, including a few wire wound resistors and removed all non-original wiring. I cleaned up all the tube socket terminals and other terminal boards. I then started building an original National NC -2-40D radio, starting 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 connector in its place. No resistor to terminate the 52 ohm coax, no Balum transformer either; so much for engineering knowledge. I used the original style lacquer covered linen and plastic solid copper color coded wire to rewire the radio. Since I didn t have any of the original paper covered foil capacitors I used the Chinese best Mylar foil capacitors. I found and purchased the original value can electrolytics. I used only the original value metalized resistors. The original BFO (beat frequency oscillator) tuned oscillator tank was in a aluminum box on top of the chassis, it had also been modified mechanically and electrically. It took some effort to remove cobbled and glued parts that connected the BFO tuning shaft to the nonoriginal 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 superheterodyne receiver, there are only two IF amplifiers, the first tuned circuit is a 455kHz. Parallel tuned tank with crystals to decrease or increase the band-pass width, followed by two additional typical dual 455kHz. tanks, mutually coupled, 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 detector 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 because of the detector. Performance and Features You probably noticed that the NC-2-40D does not have a typical band spread control, it doesn t need one because it has separate bands for 10, 20, 40 and 80 meter ham bands. The air trimmer capacitors 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 constant 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 Five
begins to rise at 10uV. The noise limiter is the typical compressor 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 measured. The radio is very quiet considering the high sensitivity and this makes for a happy user. nication receivers are better in sensitivity 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 Maybe two or three conversion commusix
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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 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 20 TH OF THE PRECEDING MONTH. RICHARD MAJESTIC PRO-TEMP NEWSLETTER EDITOR, SEND ALL SUBMISSIONS IN WORD FORMAT, PICTURES IN *.JPG FORMAT TO: RMAJESTIC@MSN.COM USPS Stamp FOR INFORMATION CHECK THE INTERNET http://www.newmexicoradiocollectorsclub.com/ Eight