The Philco 60 Repair That Almost Wasn't
From Colorado Radio Collector's "The Flash!!"
| Ed Brady | 12/99 |
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I picked up this Philco cathedral radio through ARC about a year ago. I would
have missed out had I fully read the ad. The ad caught my attention because it
listed a Philco 60 for sale for an amazing price of $20. What I failed to read
was that the ad was for the cabinet only. I did not find out about my oversight
until I inquired about the radio. Through the course of our conversation, the
original owner indicated that he had removed the original chassis for use in a
Philco radio bar. However he did have a Philco 60 chassis that someone had given
him that he would throw in for another $10. So for $30 plus $10 shipping I had a
complete Philco 60 cathedral. When the radio arrived, I was pleasantly surprised.
With the exception of the wrong grill cloth and a speaker that needed re-coning
the radio was complete and in good condition.
The Philco 60 was one of many cathedral radios that Philco manufactured during the 1930's. This style of radio was very popular and Philco built them by the thousands. This particular model was manufactured in 1935 and is what I would classify as a medium size cathedral. The cabinet measures approximately 11.5 inches wide, 8.5 inches deep and 16 inches high. I began the restoration process on the cabinet. As purchased, the cabinet was in very good condition. It had a few scratches and dings but the finish was still very nice. I began the restoration by cleaning off the gook and grime. I used #0000 steel wool and mineral spirits to do this. Next I used some Min-Wax dark walnut stain to touch up the scratches. After letting the cabinet dry over night, I finished up by applying several coats of toning lacquer to bring back the shine of the original finish. I completed the cabinet restoration by installing the correct grill cloth. Unfortunately I had to install reproduction cloth but it was of good quality and accurately reproduced the original. I buy my grill cloth from John Okolowicz. I have been very pleased with all the grill cloth I have purchased from John. It is very high quality and reasonably priced. You can obtain samples by sending a self-addressed envelope too: 624 Cedar Hill Rd., Suite 100 Ambler, PA 19002 The next order of business was to get the speaker re-coned. Before I sent it off for repair, I checked the field coil and audio coupling transformer windings. The last thing I wanted to do was to re-cone a speaker with an open field coil. Using a schematic and DVM, I was quickly able to measure the resistance of the field coil and primary winding of the audio matching transformer at 1100 ohms and 390 ohms respectively. These values were very close to the values called out on the schematic. The secondary of the audio matching transformer and speaker voice coil are connected in parallel and thus the integrity of each winding could not be ascertained by simply measuring the resistance at the terminals of the transformer. The problem here is that both windings are connected to the same two terminals and their respective resistance were on the order of a few tenths of ohms (well below the accuracy of my multi-meter. Either winding could be open and I would not be able to tell because the other would give me a resistance reading on my multi-meter. I carefully removed the speaker coil winding wires from the tabs on the matching transformer and verified that the secondary of the transformer was ok. I did not bother with the voice coil since it would be replaced when the speaker was re-coned. With the windings on the speaker verified, I was ready to send it off for re-coning. I use the Speaker Shop in Colorado Springs for all my speaker repairs. They do an excellent job at a good price. It cost $20 including shipping both ways to have this 8 inch speaker re-coned. If you would like to use them they can be reached at: 1839 North Circle Dr. Colorado Springs, Co. 80909 719-475-2545 I would suggest that you call them and discuss pricing etc. before sending off your speaker. With the easy work completed, I was ready to tackle the restoration of the electronics of the radio. The Philco 60 is a 5-tube superheterodyne receiver (schematic in Riders 4-32) designed for the reception of standard broadcast 530 - 1600 KHz as well as short wave from 1600 - 4000 KHz. It uses an intermediate frequency of 460 KHz for the IF amplification stages. The radio uses a type 6A7 tube for the first detector and local oscillator. A type 78 tube is used for an IF amplifier, a type 75 for the second detector and first AF stage, a type 42 tube as the second AF amplifier and a type 80 tube as a rectifier. A quick inspection of the under side of the radio showed that the two large electrolytic capacitors had leaked their electrolyte leaving blobs of white gunk on their terminals. There were several paper capacitors connected to terminals on the bakelite block condensers indicating that someone had repaired the radio during some point of its life. Given the condition of the filter capacitors, I didn't feel there was a need to power up the set and I began the electronic restoration by replacing the two electrolytic capacitors. I replaced them by disconnecting their terminals from the circuit and installing new 10uF, 450 Volt electrolytics in their place underneath the chassis. The value of these capacitors is slightly larger than the original 8uF units, but the difference won't matter in this application. I left the original can capacitors installed in the chassis so that from the top, the radio looked original. The next issue was what to do with all the bakelite block condensers. Given that someone had already installed replacements across several of the condenser terminals, my guess was that most of them were bad. I decided to be safe and replace them all. There appears to be two schools of thought when it comes to replacing these blocks. One is to simply install new capacitors via the lugs of the condensers and leave the old capacitors in place inside the blocks. The other is to remove the guts of each condenser block and place new parts inside. Once repaired, the condensers can be resealed using wax. I personally always use the second approach. I do it for two reasons. First, sometimes these capacitors will eventually short even if they are not exhibiting this condition at the time of the repair. Second I think that installing new components via the tabs just makes the under side of the chassis more cluttered and harder for the next person to repair 5-10 years from now. The biggest problem with these block condensers is knowing what is inside. Luckily the schematic I had numbered and provided values for all the components. Thus I could use the schematic and the numbers to determine what was inside each block. For those of you that do not want to take the time to figure all this out, AES, Antique Radio Classified and other sources sell "The Radio Collectors Guide to Philco Block Condensers" which is a comprehensive reference guide to all the bakelite block condenser types used by Philco. If you are an avid Philco collector this is a valuable resource to have. Repairing these blocks is quite easy although it does take a little time. Once removed from the radio, I can usually completely repair one in under 5 minutes. When removing the condenser blocks be sure to mark all the connections so that you know how to reinstall it later. Once I have the condenser block removed, I use a small flat head screwdriver to carefully remove the wax (or what ever it is) from the inside of the block. Continue the process of scraping the wax material out of the block until the components are completely exposed. Don't worry about damaging the internal capacitors since they are going to be replaced anyway. Once the capacitors are exposed, take the end of the screwdriver and gently lift each capacitor out. This will usually require you to use the block case as a lever point. However be careful because the bakelite housing is easily broken. I complete the removal process by cleaning out the remaining filler material once I have everything else removed. Now I am ready to install new components and place the block back into the chassis. Some people also go as far as refilling the block with wax or other material. I however do not. Once reinstalled no one can tell whether or not this has been done so I don't. Besides it makes it easier to repair should I ever have too. The next step was the check all the resistors for excessive drift in their values. I found several that were out of tolerance so I replaced them. Through discussions with other collectors I had learned that the coils in the early Philco radios were notorious for failing. This radio was no exception. Using my milti-meter I checked the windings on all the coils in the radio. My checks revealed that the primary of both the antenna and oscillator coils were open. One by one I removed each of the bad coils and inspected each for damage. I was lucky on the antenna coil. The break in the primary winding of this coil was located at one of the two connection pins. I was able to strip off the insulation at the end of the broken wire and re-attach it to the pin. I was not so lucky on the oscillator coil. The primary winding on this coil was covered with green copper oxide that told me the insulator coating on the wire was badly damaged and the windings were corroding. This winding would need to be completely replaced. The keys to successfully rewinding these coils are to use the same gage wire, carefully counting the number of turns used, and insuring that you wind the wire back on in the original direction. Maintaining the correct direction of the windings is often overlooked but it is critical to the operation of the circuit. The direction that the coil is wound determines the direction the current flows through the wire and thus determines the direction of the induced magnetic field. The magnetic field in turn is what generates the induced voltage in the secondary coil. Winding the coil in the wrong direction will change the direction of the magnetic field and in turn reverse the polarity of the induced secondary voltage. This will usually cause the circuit to function improperly. I began the retro fit of the oscillator coil by first determining the direction of the winding. Next I disconnected one end of the coil winding from it's binding post and began unwinding the coil being careful to count each turn as I removed it. During the process of removing the windings I encountered I encountered four breaks in the wire. The severity of the breaks can make it difficult to accurately count the turns so be careful. Once I had the original winding removed, I began the replacement process by carefully winding #40 gauge magnet wire back onto the coil form. When doing this be careful to place the new turns back onto the form as close to were the original ones were as possible. The length of space that the turns occupy effects the inductance of the winding so be careful not to leave big gaps between turns. Once I had the new winding installed, I used a hairdryer to gently heat the wax on the form so that it would capture and bind the new winding in place. I then wrapped the winding in electrical tape to insure that it would not move. Once I had both coils repaired, I reinstalled them into the radio. During the course of restoring the electronics, I uncovered several areas in the circuit that did not match what the schematic showed. First I found that the resistor divider latter for the screen grids for the 6A7 and 78 tubes was missing R22 and had different values for R19 and R24. I also found that the cathodes for the 6A7 and 78 tubes were not biased together via R9 and C8. Instead they were biased independently. These changes puzzled me but I did not believe they would effect the operation of the radio. At this point I decided to leave the changes in place and see if the radio would work. With the initial restoration complete, I connected the radio to my variac and turned it on. At about 90 volts the radio sprang to life on the AM band though the reception was weak. I was unable to pick up any stations on the short-wave band. At this point I decided to check the alignment of the set. With just a little tweeking of the compensating condensers I was able to get the radio playing really well on the AM band. The short-wave band was still dead however. With the band selector switch set to the short-wave position, I checked the oscillator and found that it was beating way too high. According to the alignment procedures, the short-wave frequency was adjusted using trimmer 12 in the schematic. However when I went to adjust it, I found there was not one. A closer examination of the radio revealed that not only was trimmer 12 missing but the trimmers for both IF transformers were not in the correct positions and that an additional trimmer was across the secondary of the second IF transformer. At this point I remembered the other modifications I had found and assumed the worst. From what I could tell someone had significantly modified the radio and now I was going to have to undo it to get the radio back into operational order. After several hours of rework, I had the radio back in line with the schematics. The biggest problem I had was trying to determine which compensating condenser was which. With the set completely reworked, I brought the radio back using my variac. This time the radio would not pick up any stations. I tried to align it but couldn't. The radio was unstable and howled no matter what I did. At this point I knew something was very wrong. I called Geoff Shearer and asked him to look up all the Riders references for the Philco 60. We found 4 or 5 additional references for the Philco 60 spread across several volumes. After examining all of them I learned that through the entire production run of the model 60, there had been four major revisions to the design. By following all of them I learned that my radio, as originally received, was built sometime after the final modifications were implemented. This meant that I would have to re-implement the modifications I had just taken out. This was quite the bummer to say the least. After another 3 hours of work, mainly trying to get the compensating condensers back into their correct locations, I had the radio working again on the AM band. The short-wave band still did not work due to the oscillator frequency being way out of band. In one of the last modifications Philco made to this radio, they removed the compensation condenser for adjusting the short-wave band and replaced it with a fixed value condenser. What I found was that someone had installed the wrong value for this condenser and thus the oscillator frequency was way off. I don't know if it was manufactured this way or if someone changed it during a repair. Regardless, once I installed the correct value, the radio worked fine. Looking back, what should have been an easy repair turned into a nightmare due to my lack of information. At the time I did not have many Riders manuals and relied on the information I had to restore the radio. The one thing I learned from all of this is to always look at all the Riders pages for a particular radio before working on it. You never know what small tidbit of information might be on that addendum page. It could save you a lot of work and headaches. I am happy with how it plays and looks now that it's restored. It's not a museum-quality piece but it is nice enough to display and use on a daily basis. It took me an enormous amount of time to restore but I look at it as a labor of love. Besides now I have a great story to tell and a radio that I bought for an outstanding price. |
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