Philco 16B Cathedral Restoration

The Philco16B is a large 11-tube cathedral style radio. My example was the Code 121 version with 5 bands. The radio had seen minimal servicing in the past and most original parts were still in place. This being the case, I decided to try to retain the original top and bottom chassis appearance if possible. The radio was purchased on eBay and had been completely disassembled for restoration by the owner.  This made shipping much safer, since individual components could be boxed separately.  The chassis had been shipped separately from the cabinet and the remainder of the parts.

The schematic and a partial parts list for the radio can be found on Nostalgia Air.  Any part number references in the text below reference that schematic.

My antique radio restoration logs

Previous Servicing


After removal of the tuning capacitor, filter capacitors, and bypass capacitor block, the chassis and remaining top components were cleaned using GoJo, steel wool, and toothbrushes.  


These radios are difficult to service with limited access to several parts.  Also, there are many documented changes which must be considered since the schematic, parts list, and parts placement diagram will likely not match the radio as built.

My usual restoration procedure is to make a complete survey of the condition of all components and repair all items before the radio is tested.  I assume that all paper and electrolytic capacitors are leaky and thus should be replaced (I always "restuff" the original components if possible). I do not replace mica capacitors, but may test them in place if possible.

Restoration Strategy

Since almost all of the original parts were still in place, and since this was going to be a "keeper", I decided to try to retain the original top and bottom chassis appearance to the extent possible. All original capacitors would be rebuilt in their original containers (restuffed), including the distinctive Philco bakelite block capacitors, the original filter capacitors, and the bypass capacitor block. Any out of tolerance resistors would be replaced with the same types if available.


Tuning Capacitor Mounting Grommets

The tuning capacitor mounting grommets were badly deteriorated and stiff, allowing the capacitor to flop around.  Unfortunately the exact replacement parts needed were not available from Renovated Radios.  The closest available part was GLg-Tuner.  While these parts fit the chassis hole and the center hole is the correct diameter, they are only 7/16" high (1/2"+ is needed since there is a 1/2" steel spacer used in the center). These grommets were extended by gluing on some GHal-S40 grommets that had been trimmed of their projections.  This additional 1/16"+ in height worked out well.  The parts were attached using super glue.

The tuning capacitor was cleaned using my old Heathkit ultrasonic cleaner and dilute ammonia.  It would not all fit in the cleaner at once, so several cleanings at different angles were needed.  I normally remove the mica trimmer insulators before cleaning in order to avoid damage.  But in this case they were left in place, since the notes in Riders indicate that the alignment of two of the tuning capacitor trimmers is factory adjusted and sealed (there are no instructions provided for adjusting these trimmers in the field - so I decided to leave them alone).  The capacitor was then cleaned using soap, water, and toothbrushes.  After drying with a heat gun, the bearings and grounding fingers were lubricated using automotive distributor cam lubricant.

QAVC Adjustment Potentiometer

The 10K wire wound QAVC inter-station quieting adjustment potentiometer 82 (on the rear chassis) measured open and also intermittent in operation.  It was removed from the set and the rivet retaining the rotating member and center terminal removed.  This allowed the resistance element to be removed for cleaning and inspection.  Unfortunately, there were many breaks in the resistance wire and the control could not be repaired.  It was replaced with a 10K ohm 5 watt linear taper wire wound control having a screwdriver adjustment slot (the original had a short knurled shaft).  The replacement control was slightly smaller physically than the original.  The original also had a tap which was not used in the radio.

Volume Control and Switch

The volume control showed signs of previous trouble, in that a piece of solid copper wire had been wound around the shaft between the retaining circlip and the front bushing, and then soldered.  I assumed that this was an attempt to increase the pressure of the rotating element on the resistance element.  The control measured a very high resistance and was intermittent in operation.  This type of control cannot be cleaned - the resistance element is nothing more than a thin film of carbon on a cardboard or fiber backer board.  A sheet of flexible stainless steel separates the wiper from the resistance element. Any attempt to clean the element will simply remove the thin carbon layer.  The AC switch on the back of the control was also defective.  The control was rated at 2 megohms with a tone control tap.  It was replaced by an NOS IRC Q13-139X control with 76-1 switch. The standard D-type shaft that comes with these controls does not fit snugly into the Philco knob.  So a piece of sheet brass was epoxied to the end of the shaft once it was trimmed to length.


The radio uses "dogbone" type resistors.  About half of them were the older "cast end" type with solid metal ends.  The remainder were later "wound end" types with the radial component leads wound around the resistance element and then soldered. Only one original resistor had drifted out of acceptable tolerance range, and would have to be replaced.  In most cases, I would replace an original resistor only if it was not within +/- 20% (or marked tolerance).  Any "dogbone" resistors would be replaced with the same type resistor.  I keep a stock of NOS and used "dogbone" resistors, and buy all I can on eBay and radio swap meets!  Of course, most of these resistors, even NOS resistors, have also drifted in value and no longer have their marked values.  My solution is to find a replacement resistor of the correct value and size as measured (ignoring the markings), and then repaint it to the needed value codes using enamel hobby paint!  In the case of this radio, only one "dogbone" resistor had to be replaced (a 10K 1 watt unit).  I found a NOS 15K 1 watt dogbone resistor in my stock that measured exactly 10K.  Thus I only had to repaint the end color black.

Capacitor Bank 62

The 5-unit bypass capacitor bank 62 was restuffed with new film capacitors.  It contained capacitors of 2.0, 2.0, 0.5, 0.5, and 1.0 mfd.  630 volt film capacitors were used to restuff this capacitor (values used were 0.47, 1, and 2.25 mfd).  This capacitor is very easy to rebuild.  Once the internal leads were removed from the top terminals and the ground connection unsoldered from the case, the cover can be removed.  I ground off the rivets on the cover, assuming they were holding the cover.  As it turns out, they were only holding the terminal board - nothing was holding the top cover other than the leads to the capacitor body inside. The capacitor pack can then be removed as a unit by sliding a putty knife or thin blade between the fish paper insulation and the metal case. Very little of the tar was stuck to the metal case.

Filter Capacitors

The two original can type filter capacitors 87 and 88/75 were rebuilt in their original cases using new electrolytics.  The wet 8mfd 450 volt unit 87 was restuffed using a 10mfd/450 volt electrolytic.  The dual dry unit (8mfd 450 volt and 10mfd 50 volt) was restuffed with a 10mfd/450 volt  and a 22mfd/50 volt electrolytic.  My restuffing process for the wet type capacitor 87 is as follows:

The process for restuffing the dry type capacitor 88/75 is similar to the above.  However all of the contents have to be removed.  Holes are drilled into the hard rubber base near existing terminals.  The common ground connection is also routed through the base near the location of the original ground lug.


Rebuilt Filter Capacitor Cans 

Paper Capacitors

All paper capacitors were rebuilt in their original cases using modern 630 volt film capacitors in order to maintain the original under-chassis appearance.  The radio used two types: most were Philco bakelite block type capacitors but a few were normal tubular types (mentioned in the CHANGES for Run 8 - 30-4020-X, .05mfd).  For the tubular types, I remove the capacitor from the radio by unsoldering its leads.  The lead lengths and any insulating sleeving lengths are then noted.  I take notes of which lead goes where in the radio, and identify the capacitor using marking tags (which note the part identification and the location in the notes where it was removed).

The tubular types are easy to restuff.  They have crimped ends retaining a fiber disc.  My restuffing process for these types is:

Restuffed Tubular Capacitor

Bakelite Block Capacitors

All original Philco bakelite block capacitors were removed from the radio (one at a time, making careful notes of connections), their contents removed, cases cleaned using lacquer thinner, and restuffed using modern 630 volt film capacitors.  Before removing the contents I unsolder the internal capacitor leads from the outside terminals and clean off the terminals. I use mechanical methods of removing the bulk of the potting tar and capacitors (small screwdrivers).  One must be careful NOT to pry against the bakelite case, as it is easily broken.  Some collectors use heat to remove the contents.  Here is the restuffed capacitor 90 (the line bypass capacitor, Philco part number 3793E), which contains two 0.015mfd capacitors:

One capacitor also contains a wire wound resistor, which was reused.

Tone Control Switch Repair

The tone control switch 79 contains two capacitors buried in tar.  The CHANGES listed in Riders indicate that the two capacitors are 0.003 and 0.09mfd.  An associated external capacitor 80 contains two 0.025mfd capacitors.  Note that these values DO NOT correspond to the schematic!  The capacitors within the switch were replaced using  0.0033 and 0.1mfd 630 volt capacitors.  The bakelite block capacitor 80 was rebuilt (as shown above) using two 0.022mfd 630 volt capacitors.  One of the two lead wires (black) had to be replaced, since it was rubber insulated and the insulation was falling apart.  The red lead, although also rubber, was OK and was reused.  The tar was replaced using melted rosin salvaged from servicing RCA Radiola Superhet catacombs. Before new parts were installed, the control was cleaned in my old Heathkit ultrasonic cleaner using dilute ammonia.  Here is the restored control:

Tuning Mechanism Vernier Drive

The tuning shaft was slipping and would not rotate the tuning capacitor.  This was due to hardened and worn rubber tires on the two drive wheels. The mechanism was removed from the tuning capacitor and the failed rubber removed mechanically (not easy).  The two rubber tires were replaced using modern O-rings as documented in an article at  The knurled shaft that engages the large rubber ring on the dial scale hub was cleaned using an Exact knife in order to remove debris and rubber embedded in the grooves.  This results in a better grip on the rubber ring.

Dial Scale

The dial scale that came with the radio was hopelessly warped, likely due to material shrinkage. I was able to acquire a replacement dial assembly with a fairly straight dial scale.  However, the large rubber drive wheel on this replacement unit was in poor condition with much material loss and wear.  The rubber drive wheel on the original dial scale was in good but not perfect condition.  So I decided to remove the dial scale from the replacement dial and install it on the original hub with the better drive wheel.  The dial scale originally was attached using brass rivets.  These were carefully ground off and replaced by 4-40 x 3/16" round head brass screws and small nuts.  The original holes in the metal hub had to be slightly enlarged to accommodate the screws.  After assembly, there remained one "dead spot" around 1400 on the dial.  The remainder of the dial worked smoothly.

Power Cord

The power cord was replaced using brown rayon covered reproduction lamp code from Antique Lamp Company.  The original AC plug was reused.

Other Repairs

The chassis mounting washers were replaced using CW-5 washers from Renovated Radios.

The pilot lamp socket for the shadow tuning unit was rebuilt.  All the deteriorated rubber parts were first removed.  The spring and center contact were saved and re-used.  I replaced the failed rubber insulation with a 3/8" fiber washer with its diameter ground down to fit loosely inside the socket.  I do this by attaching several fiber washers to a long 6-32 screw and then grind their outside edges on a bench grinder until they can slide into the Philco socket.  This way I make several spares, since all Philco radios seem to have this problem. The original power lead was also re-used and secured behind the fiber washer using two layers of 1/8" heat shrink tubing. The position of the lamp is critical and has to be adjusted by bending its mounting bracket once the radio is reassembled and tested - it affects the appearance of the shadow tuning meter face.

The broken/missing GROUND connection (a Fahnestock clip) was replaced using a similar part I found in my junk box.  The original was attached with a rivet.  I secured it using a 6-32 screw, which also retained a ground lug on the back side. The 6C6 tube substitute was replaced with the original type 77 (although the 6C6 is a close substitute).  A defective type 77 (Philco) was replaced.  Breaks in the speaker cable and wiring to the QAVC switch were repaired using heat shrink tubing.


The cabinet was in excellent shape.  It was cleaned with GoJo hand cleaner and 00 steel wool, followed by a coat of Johnson's Paste Wax.  The knobs were cleaned with GoJo and then lightly polished on a bench grinder small soft buffing wheel using plastic polishing compound.


After the radio was completely reassembled, power was applied through a wattmeter and fused Variac.  Power was brought up slowly while monitoring the B+ voltage and the wattmeter.  The radio came alive and worked - no assembly errors!  The radio was then aligned, which is a complex process and required careful reading (I went through the procedure twice just in case).  The shadow meter worked OK after adjustments documented at The Philco Repair Bench Service Hints and Tips. The QAVC inter-station quieting feature worked, but was very difficult to adjust.  Likely this was due to a large amount of noise/buzz in my shop - there is really NO quiet place on the dial on band 1.  If the control was adjusted to eliminate all the noise, the weak stations were also eliminated. This may be normal, since this radio was made before high levels of AM interference from power lines, fluorescent lighting, wall wart power supplies, and computers existed.

While the radio appears to be quite sensitive, the AVC voltage only varies from about -0.5 volts (off station) to -5.5 volts (strongest local station).  However, we are located in a rural area and my antenna is only a 40' length of wire strung across the basement ceiling.  This lack of available signal and resulting small AVC voltage range is likely the reason there is little movement of the shadow meter. 

I first thought that the B+ was low: 277.5 volts at the 42 output tube plates, vs. a spec of 340 volts (116 volts AC input). However, there appears to be no published voltage measurement table for the Philco 16B code 121.  The voltages for the code 122 are higher, but that set uses a different power transformer, speaker field, and a 5Z3 rectifier (vs. an 80 used in the code 121 set.)  My B+ voltages were similar to those in the voltage table for the code 125 set, which ALSO uses an 80 rectifier.  I also own a Philco 16 code 121 tombstone.  Its B+ measured the same as those in the 16B cathedral.  So I will assume that the B+ voltages are OK.

Restoration Results

Most of my restoration objectives were met, but not all.  There was no intention of restoring the set to factory new appearance!  My objective is usually to reverse any prior servicing and make the radio appear to have never been repaired.  I do not go so far as to artificially "age" solder joints, as do some collectors!  Nothing gives away a restoration faster than bright and shiny solder joints.  Here are some of my "misses":

Before and After Restoration Photos

Chassis Before Restoration

Chassis After Restoration