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The Silvertone 1942 (later version) from about 1936 is
a large 8 tube superhet tombstone radio that receives the broadcast band
and two short wave bands. It has a large speaker and push-pull
outputs. It also has a two-position switchable bandwidth IF stage that acts as a
tone control (it also has a separate normal tone control). The set
has a tuned pre-selector on the broadcast band, but has no RF amplifier
stage. The set
is unusual in that it uses metal-glass tubes, an early and short lived
competitor to RCA's metal tubes! It appears to have
been made by Colonial Radio, and the build quality is quite high.
The radio had seen NO servicing that I could find - all the original parts were still in place, even the power cord. I decided to try to maintain the original above and below chassis appearance to the extent possible. The schematic for this radio can be found on-line at Nostalgia Air. |
My antique radio restoration logs
This radio was purchased on eBay. Unfortunately the cabinet has been stripped of its original finish. The grille cloth also MAY have been replaced. The knobs were original. The radio was sold as working on the broadcast band with scratchy controls (the seller did not know what the controls did!) There was no shipping damage.
There was no signs of electrical restoration or even repairs! I always avoid knowingly purchasing a radio that has been restored by a collector, as many take shortcuts such as removing the original capacitors and filters. When tested, the radio actually did work as stated, so all major parts should be OK.
The 5Z4MG rectifier had been replaced by a 5Y3GT. All the rest were likely the original Silvertone branded metal-glass tubes with similar date codes! The 6E5 eye tube was also branded Silvertone, but may have been a replacement.
All the original resistors were still in place.
All the original capacitors were still in place, including the filter capacitors (which still had liquid inside and actually worked!)
The AC plug had likely been replaced.
Even the line cord was original, but in poor shape.
My usual restoration procedure is to first make a complete survey of the condition of all components. The survey results guide my restoration strategy. If major and unique components are defective or missing and cannot be restored or replaced, I may elect to sell the radio rather than restore it. I always assume that all paper and electrolytic capacitors are leaky and thus should be replaced (I always "restuff" the original containers if possible). Any mica capacitors are assumed OK until testing proves otherwise. Since the radio actually worked, at least on the broadcast band, no major components were defective (RF coils, chokes, transformers, RFCs, etc.)
All tubes were removed. The tuning capacitor and dial assembly was removed for cleaning and access to other parts on top. At this point I made BEFORE photos of the chassis bottom. I use these photos to ensure that replacement parts and wiring are placed as close as possible to their original positions. Some radios are subject to problems (such as oscillation) if wiring is re-routed or lead dress is not the same as the original..
The top and sides of the chassis was cleaned with GoJo hand cleaner and 00 steel wool. Since this process may leave small steel wool fragments that can cause problems later, I follow up with a thorough vacuuming and go over everything with a small magnet and masking tape to pick up any stray fragments.
The power cord was simply shortened to eliminate several unsafe or broken areas. A more suitable old-style bakelite plug was installed. Some of the outer cloth braid is missing, but the inner conductors are now safe to use.
New tuning capacitor grommets were installed. I used type GLg-Tuner available from Renovated Radios.
The fuse holder ends were strengthened using solder. A 1-amp fast blow fuse was installed in the holder.
All of the original capacitors were restuffed using new 630 volt film capacitors. Most all were branded Sprague, with a few CD "Tiger" brands. Here is the process I use when restuffing capacitors. In order to maintain the underside chassis appearance, the out-of-tolerance dogbone resistors were replaced with the same or similar types. I maintain a collection of NOS and used dogbone resistors. Of course, most of these are also out of tolerance! So I select a resistor from my stocks that has drifted to within 15-20% of the needed value, and then repaint it to the needed value using hobby paints. In a couple of cases, I did not have a suitable 1/4 watt dogbone resistor that was usable, and I was forced to use a 1/2 watt resistor for R6 and R12.
The filter capacitors (14mfd and 8mfd) were rebuilt in their original cans using new 15mfd and 10mfd 450 volt electrolytics. My rebuilding process is as follows. First, the insulating cardboard sleeve was removed from the input filter capacitor - in this case there was no problem - but sometimes they are firmly glued on and cannot be removed without first splitting the cover. The capacitors were then chucked in my Unimat lathe and their cases deeply scored about 1" up from the bottom. The cuts were then completed using a hobby razor saw and cleaned up using an Exacto knife. This leaves only a thin straight line on the case - hardly visible. The original contents were then removed and the capacitor case cleaned inside and out. The original positive foil was removed and the stud was cut short and then drilled to accept a ground lug and 4-40 screw and nut. The positive lead of a replacement capacitor was attached to the ground lug. The negative lead of the new capacitor was extended, insulated using spaghetti tubing, routed though a small hole drilled into the base close to the threads, and attached to the original nut after the capacitor was mounted. The two halves of the case were rejoined using 3/4" plumbing PVC couplings which were wrapped with masking tape and secured using epoxy. The masking tape was needed to slightly increase the diameter of the coupling, and also perhaps permit the capacitor to be re-opened in the future, if needed.
All of the original metal glass tubes were left in place. I was able to find an NOS replacement 5Z4MG tube on the Antique Radio Forums Classified Ads. The original 6E5 eye tube was also left in place. It is dim, but usable (at least in a dark room!) The radio worked very well even though the original 6Q7MG and 6A8MG tested weak. I wished to maintain use of the original tubes if possible.
There's not much I could do with the cabinet, since the original finish had been stripped (and NOT refinished). I simply left it as is. At least it will be a simple refinish job for some future owner, since the messy part (stripping) has already been done, and the cabinet wood has no grain that has to be filled. New chassis washers were fitted. I used part CW5 available from Renovated Radios. The lettering on the wooden knobs was refilled as much as possible using gold lacquer stick. The knobs were placed on the correct shafts! The missing chassis bolt was replaced using a standard 10-32 round head slotted machine screw, plus a flat washer. The missing rubber centering insert was fabricated from a rubber bushing (not as long as the original, but it worked). One missing metal disc which fitted under the chassis washer and allowed adjustment of the chassis height was replaced using a knockout from an electrical box - which was almost identical to the three remaining originals!
Once the radio chassis was reassembled and the tubes installed, power was brought up slowly using a variac. AC power consumption was monitored using a watt meter, and a DVM monitored the B+. When first tested, the radio powered up but there was only some crackling noises and a few very weak stations received, even at full volume. It was discovered that the secondary of the second IF transformer had opened up - broken wire at the terminal. This could have been caused by removal and replacement of the transformer's top nut for cleaning the shield. Once this was repaired, the set worked well, even with the weak tubes (6A8MG and 6Q7MG).
The radio was then aligned, which was more difficult than usual since the trimmer locations are not indicated in Riders (Nostalgia Air) - but easily determined using a DVM by selecting each band and measuring the resistance to each trimmer. The radio performs very well, is quite sensitive and has very good tone. As is typical of radios of this age, there is excessive speaker cone movement on some stations if the tone control is set so as to increase the bass. I am told that today's stations have much more bass then in the 1930's (classic country or classis rock). The switchable selectivity IF works well - essentially a selection of WIDE or NARROW bandwidth. WIDE (position 2) sounds best for music. I suppose that NARROW (position 1) would be used when listening to short wave stations which are close together.
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