|The Zenith 8H032 from 1946 is an 8-tube AC Superhet that
receives the broadcast band, the old FM (FM45) and new FM (FM100)
bands. This radio would have been used during the transition to the
new FM band (88-108mhz) starting in 1945. The old FM band is no
longer used for broadcast radio.
The schematic for the 8H032 can be found on-line at Nostalgia Air. For this restoration I had an original SAMs Photofact, which is fortunate since the Nostalgia Air schematic is very difficult to read.
The radio had seen major servicing in the past. Many paper capacitors, the filter capacitor, and perhaps all the tubes had been replaced. I decided to try to reverse these repairs and to restore the set to its original condition to the extent possible, yet get it working.
My antique radio restoration logs
This radio was purchased on the shopgoodwill.com auction site. This site combines items from many different Goodwill stores under a common auction site structure with search, auction style bidding and checkout capability. The radio appeared complete and in good condition, but was stated as not working. The knobs, bezel, dial cover, back cover, and grille cloth were all present and apparently in good condition. The listing noted some alligatoring and other finish defects. Unfortunately, the radio was not packed very well, and was delivered by UPS (not a good combination). The radio was in pieces when received. Previous experience with UPS claims has shown that UPS will not honor an insurance claim if the item is not packed sufficiently and/or there is no visible damage to the carton.
So I decided to request a refund (fortunately available from this particular Goodwill store). I sent them photos of the damage, and they refunded my debit card the full amount including shipping and handling costs in a couple of days. They did not request the radio (in pieces) back, but did later file a damage claim with UPS (which UPS likely paid, since this was only a $40 radio). So since the radio was basically free, I decided to at least attempt restoration IF the cabinet could be repaired. Otherwise, I would keep it as a possible future parts set when I find a better example.
All tubes had likely been replaced at some point. None were Zenith branded. The 5Y3GT had been replaced by a 5Y3G.
Seven wax-paper capacitors had been replaced (the usual suspects: the audio coupling capacitors, the limiter screen bypass, the line bypass capacitor, and several tone control capacitors including the output tube plate capacitor). Some were in very difficult-to-replace locations, so likely someone paid a lot of money to have this radio serviced.
There were several Sprague capacitors without Zenith part numbers. I assumed that these were replacement, but I was not sure. I have seen many Zeniths with Sprague capacitors, but these all had Zenith part numbers.
The LO BASS tone capacitor (.005mfd) had been replaced with a .001mfd unit. I'm not sure why, unless this was an attempt to reduce excessive bass (which does happen with modern radio stations).
The three-section filter capacitor had been replaced.
One resistor had possibly been replaced by a modern 1 watt type - unlikely due to a failure (tone circuit) - perhaps it was damaged when a paper capacitor sharing a terminal was replaced!
There was tape on the FM line cord antenna lead and on the 6S8GT grid cap lead because of failed insulation on the rubber covered wiring.
The line cord plug had been replaced - the line cord was original but not usable.
The grille cloth was secured to the cabinet using large tacks. It would have originally been secured by staples, which may have pulled loose when someone pushed on the grille cloth.
The dial bezel had been secured by two round head screws at the bottom, and two 4-penny NAILS at the top (bent over behind). The screws were larger than the originals would have been and were the wrong type. Perhaps the screw holes in the cabinet were damaged and would no longer hold the original screws.
The speaker cone surround had been coated with some paint-like substance, and cotton had been stuffed between the cone and speaker basket on the back. I have no clue what this was supposed to accomplish. There was no obvious damage to the speaker cone, and testing showed that the speaker worked (although I was not sure what it would sound like in the completed radio). Perhaps there was a rattle.
The back cover had breaks near the bottom and had been patched back together using tape.
The dial cord had been replaced.
The pilot lamps had been replaced with the incorrect types.
My usual restoration procedure is to first make a complete survey of the condition of all components. The survey results guide my restoration strategy. I never apply power to a radio before restoration, even through a "dim bulb tester" or variac "to see if it works". If major and unique components are defective or missing and cannot be restored or replaced, I may elect to sell the radio for parts 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.
Before starting the detailed chassis component survey or any repairs, I first had to make sure I could reassemble the cabinet and that the radio would be presentable afterwards. Otherwise it would make no sense to restore the chassis. The cabinet was basically in several pieces:
First, repairs were made to each subassembly using Titebond II carpenter's wood glue and suitable clamps. First the bottom, one side and front were re-glued and clamped. The remaining parts all interlocked, so they would have to be glued and clamped all at once. The reassembly process was first planned by dry fitting the pieces together and determining the clamping strategy. Once all the clamps and pieces of cardboard and waxed paper used to protect the finish were arranged, glue was applied, clamps applied, and the glue allowed to dry overnight. The result was quite good, but there was some damage visible is one closely examines the radio. The result is shown below:
Before starting repairs I made BEFORE photos of the chassis top and 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 or feedback) if wiring is re-routed or lead dress is not the same as the original. Plus, I prefer to keep the under chassis appearance as original as possible.
All tubes were removed. The dial assembly was removed. The chassis was dusty, but had no rust. It was first cleaned off with an air compressor. The top and sides of the chassis were then cleaned with small bottle brushes and a toothbrush.
The FM antenna lead and 6S8GT shielded grid cap lead were replaced. Several other rubber covered wires with deteriorating insulation were replaced. I used both solid and stranded cloth covered wires (8 colors) for all replacement wiring. I use the non-rated (smaller diameter) 20 gauge solid and stranded wire available from Radio Daze. The AC line cord was replaced with a modern vinyl replacement.
|Most of the leads to the tone switches were replaced (2 of the wires were still usable). First the leads were unsoldered from the switch assemblies. The lead colors and lengths (projections from the clear plastic sleeving) were measured and documented. Next, the plastic sleeving was removed by first heating with a heat gun. Next, each wire was removed noting its color, attachment point, routing (through which hole in the rear chassis) and total length. I did not have a suitable replacement color for the gray wire used, so I used black, which was otherwise not used. The above procedure was reversed in order to reassemble the wiring to the switches. Before assembly, the switch contacts were cleaned in my old Heathkit ultrasonic cleaner using dilute ammonia, followed by soap, water, and a toothbrush. Only the contact portion of the switch levers were cleaned in the ultrasonic cleaner, in order to avoid possible damage to the lettering.|
The dial cord was tightened by adding another turn on the tuning shaft. The play in the dial pulley was eliminated by peening over the soft metal of the collar projecting through the pulley.
The original power supply filter capacitor C19/C20/C21 had already been replaced by a Sprague TVL 3787 twist-lock capacitor with a date code 7130L (30th week, 1971). I normally would replace or restuff any filter capacitors. However, in this case I decided to at least test it first, since Sprague capacitors are very high quality units. First I reformed one section. It only took about 5 seconds to reform to 450 volts using my current-limited capacitor reformer, set at 6ma. And it measured 40mfd using my HP973 DVM. I next tested it using my Sprague TO4 capacitor tester. The leakage current was less than 100 micro amps (more like 50 micro amps - difficult to read), capacitance was 45-50mfd, and power factor 9%. So I decided to leave it in place pending the completion of the restoration and testing. To remove this capacitor for re-stuffing would have required removal of several small parts for access. And it was not obvious if I could find capacitors small enough to fit inside the can for re-stuffing. It would have require two 47mfd at 450 volts and a 47mfd at 25 volts.
All the original Zenith paper capacitors were rebuilt in their original cases using modern 630 volt film capacitors in order to restore or maintain the original under-chassis appearance. In cases where an original Zenith capacitor had been replaced during servicing, I found a suitable original dud in my parts bin and restuffed that capacitor. I collect branded capacitors (Zenith, Philco, and others) just for this purpose. I have been able to purchase Zenith and other branded duds from collectors on Antique Radio Forums and on eBay who do not restuff capacitors. 24 capacitors needed rebuilding. In most cases I found a dud with the part number listed in SAMS. In one case, I did not have the exact part, so I substituted a capacitor with a similar Zenith part number having the same capacity and voltage rating. My re-stuffing process is as follows:
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+. The radio came alive immediately and worked on both AM and FM bands. However, both AM and FM needed alignment. The AM alignment was completed, and most adjustments were close except for dial calibration. The FM100 band was working well on just the "line cord antenna", and I am in a rural area. So I limited the FM alignment to just the discriminator and dial calibration - I did not mess with the IF transformers (as recommended in SAMS). The speaker seemed to work OK - at least there was no rattle. It is hard to judge what the effect of the white substance on the cone surround might have been, since I do not have an original to compare with. There was hardly any hum, and I measured only about 0.4 volts AC on the B+ line. So the Sprague filter capacitor seems to be doing its job. But since it is 40 years old, it could of course fail at any time. But this radio will not be a daily driver.