Midwest Radio Console Model DD-18 (18-36)
Restoration

In July 2013, I was contacted over a radio sale. The owner of the radio told me that "he had a very great radio and that the mark was Midwest ...” Without having a device with this brand and with the data received over the phone, I searched on www.museudoradio.com  . The first impressions were good and I foresaw a radius of real value to the collection. Seeing him, first impressions were confirmed and the negotiation was successful.

This is a receiver manufactured by U.S. Company Midwest Radio Co., Cincinnati, Ohio, Model DD 18 and chassis type 18-36, the year 1936. A huge radio with cabinet in hardwood console of one meter and twenty-two inches tall and 18 valves!

The state was very problematic. Although it was with the chassis and apparently intact box, the dirt, termites and some attempts to restore the electronics did more damage than recovery.

Cleaning and testing the input transformer

Aside from the dust that was not distinctive parts of the chassis, wiring, capacitors and other components were damaged or misused. The input wiring AC and the output DC (+ B) there was a situation of almost short circuit. Among many other flaws and adjustments with the originality, the speaker was not the electrodynamic model, but of permanent magnet. The output transformer of the double push-pull (4 valves 6F6) was replaced by a distinct in relation to the possible factory values.

After cleaning the chassis, isolating the input transformer of the rest of the chassis, I checked possible short circuits. I made measurements in ohms, have sorted the wiring and transformer called and voltage measurements were correct: high voltage and 5 V for the two 5Y3 (5Z4 original) rectifier valves, and 7 volts for the filaments and lamps in general (6.3 VAC). The input and transformer wires were remade.

Speaker and output transformer in push-pull

The next step was the difficult task of getting an electrodynamic speaker (with choke coil) and large diameter. The DD -18 was a non- original speaker (permanent magnet) with 15 inches of diameter. The most I could get the stock was an electrodynamic speaker 10 inch, U.S. origin and coil 2000 ohms, identical to the original value.

The second difficulty was about the output transformer in push-pull. The former had 80 and 100 ohms on each “side”. Not having the original values ??of the manufacturer opted for a transformer output with about 180 ohms on each side of the push-pull.

Identifying parts

I had never faced a receiver with so many tubes! The larger chassis I restored until then had 10 valves. Aside from the double -rectification and double push-pull had new functions to search and recognize. One way was by making a list of the 18 valves and their functions, based on the Midwest Radiomuseum.

The receiver has six wave bands. Each track has marking in frequency and meters with trimmers for calibration. Watching the dial and descriptions of the Midwest Radiomuseum, are in descending order:

Analyzing and reviewing tensions

Once put " in charge" (with all valves connected to the + B ) noted that tensions were excessive for the circuit , a constant in the restoration of receptors that have been made ??to an original voltage of 110 VAC season compared to 127 VAC current present . The easiest solution was to place a resistance of 5 ohms for 50 watts at 127 VAC input (125 volts the middle voltage of my workshop), which lowered and stabilized the output transformer more “calm” values ??line (photo below).

This resistance was put in a safe place the chassis due to heating. This way I could leave the stresses of the plates 4 6F6 output valves (two in parallel push-pull ) and the values ??of B + lowest of those submitted by hand at the factory and found in the table above in the site:          http://www.midwestradiomuseum.com.                                         

In my experience, I have habit of leaving the values ??of the voltages slightly below those maxima manual valve, factory tables and schemas, since, besides the 15% increase in current supply voltage, valves and other components have 70 or more years old ! Operating today a radio of the 1930s or 40s with voltages in the same limit when it was manufactured is the same as requiring that a citizen with 80 years old run the same way as when he was 20 years…

Thus, the output voltage of the cathode of 5Y3, chock after the filter and coil speaker, was in the order of 440 VDC representing a voltage around 300 VDC for the plates of the 6F6 and 240 + B more compatible than the values ??of 370 VDC shown in table factory to the plates and the outlet valves 320 to the +B.

Other stages of the electronic restoration

As usual and urgent necessity electrolyte were removed and restored by inserting new capacitors in the old original aluminum casings. Thus, the four electrolytic capacitors filter have been summarized in two units, each containing two new capacitors with higher values ??(22 - 47 microfarads) than in the original scheme (image). The other electrolytic and common capacitors and resistors were replaced with the factory values ??.

The Panel

A cleaning with sandpaper and steel wool and retouching with aluminum paint left the dial looking new (pictured right). The dial of the Midwest DD - 18 recalls the symbol of flying (wings of an airplane) and has four control knobs on. The center is the line that splits into two with vernier knobs, for a fine tuning. Below this are the wave selector switch and volume controls and tone. Among the latter there are two push- buttons. The left is called " silent tuning push button” that cuts all the sounds for the adjustment of a new season: the audio for quiet tuning. On the right is the whistle: the radio emits a high frequency also varies according to the desired station tuning. After almost 80 years of its manufacture , the "ocean " noise and radio frequency interference that flood our homes and the blurring of AM stations and OC , gives these controls a mere historical aspect .

The panel lamp (tunalite) low brightness every time a station is tuned. To this end there is a valve V16, one 6C5 tube.

Unlike most other radios where the pointer drifts on a fixed dial, the DD -18 there are two light “fixed pointers” (above and below the circular dial) composed of a "gap" light . They are the luminous pointers where spins circular plastic dial. The light from the bottom was destroyed and I need to produce one using thin plates of old computer diskettes. Above this blade was glued a piece of cardboard to match the color of the “pointer” enlightened, as the photos below.

The cabinet

The Midwest DD -18 is a receiver with cabinet called by “radiophilous” floor, as a mobile supported directly on the floor. This is an example of a mobile Art Deco of the 1930s. It has a large vertical dimension (1.21 m after deducting 0.5 cm supports felts), 68 cm wide and 42 deep. Those who restored the chassis feel its enormous weight: the complete set exceeds 40 kilos!

The wood seemed no major problems until I decided to replace the front fabric. The friend Sergio Caon moved the floor just below the speaker: I almost had a heart attack upon seeing the volume of wood destroyed by termites!

Carpenters Midwest or the company that manufactured the cabinets was not careful to put a wooden beam of such poor quality (white pine) in a hardwood cabinet ... and it is well hidden inside. Thinking the work had already finished, I saw that It was far from over. There was a lot of work ahead! Although termites were not already there, I would not expect to return: it was done the traditional bath of liquid to kill termites

Then, any loose parts removed and some more inner areas filled with plastic mass with catalyst to increase the rigidity of the timber. The finish was decent for me to spend countless hands mass for wood volume. So I filled with common plaster and sanded the surface. Below are respectively, the two work phases.

The piece of wood section of 2.5 cm x 2.5 cm (batten) that appears at the top of the restored beam was included to allow a better finish plaster. It was a week of hard work for all the senses: the heavy cabinet had to be standing or lying position to each face fill and sanding plaster...! After many coats of paint and sandpaper, there are the photos below.

The Tissue

The cloth that covered the speakers was completely torn and unrecoverable. The great friend Daisi Guindani donated a few meters of a suitable fabric brought from Uruguay Republic. Following photos below, the change of the support slats and the final appearance of the fabric are presented.

The Final Touch

The chassis was painted with automotive lacquer paint in aluminum color. Below the chassis ready and metallic stickers, shown below with their metallic labels featured.

Midwest Model DD-18 (18-36) Console Radio, 1936, USA.

Take a look at the radio running: https://www.youtube.com/watch?v=mZzhGWBXBCU&feature=youtu.be

Thanks to :

Brazil
Arthur Victoria D’Arisbo, son and website manager
Daisi Guindani, great friend
Sérgio Moraes Caon, friend and radio partner

Canada
Jean Yves Bourget, great friend

USA
Philip I. Nelson    http://antiqueradio.org/MidwestDD-18.htm 
Mike Simpson      http://www.midwestradiomuseum.com           

Radio AntiqueRadio OldRadio Collection Daltro DArisbo
Todos os direitos reservados Museu do Rádio®