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Philco 116X cap question - Printable Version

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Philco 116X cap question - Hamilton - 12-01-2025

https://philcoradio.com/library/download/service%20info/service%20bulletins/Philco%20Service%20Bulletin%20222A.pdf

I have a Philco 116X and although it’s probably too complicated for me, it was free so I will do my best.

I’m working on Part #83, a 4 section electrolytic, which was missing from the radio when I was given it. I could figure out where the 1 mfd cap that comes from the 77 1st audio tube, black arrow on the photo, but not the other three caps.

The attached photo shows my 30K resistor attached to pin 3 of the 77 tube and the 10K attached to pin 2 of the 76 tube. They are then attached to different lugs on bakelite block Part #44. That terminal strip was added at sometime, with #99 a 13K resistor and #98 connected together. Is this correct? I cannot trace how #97, the 30K connects to #98. 

Also I can’t find the 10K resistor that the other black arrow is pointing too on the radio. The number they have assigned to it, either #101 or #104, doesn’t correspond to anything on the parts list.

I can’t follow schematics well yet and I have trouble explaining what I need to know but I would appreciate any and all advice on how to connect the other caps of Part #83.

RE: Philco 116X cap question - MrFixr55 - 12-01-2025

Hi Hamilton,
First off, this is a rather high-end radio for its time and certainly worthwhile repairing.  You will have a nice sounding radio when done.  Consider adding a Radio - Aux Switch when done, so you can pipe big band music or old time radio directly int the set. 

This is more complex than the average radio, and pre-WWII radios have some interesting features on power supplies that post WWII radios don't have, but do not be discouraged about not being able to read schematics, first off, we will be very happy to help you!  Second off, google reading schematics and you should also find help.

You already have some skills as you found the section of Cap #89 that connects to the screen grid of the 1st Audio Amp tube.

Below is a schematic representation of a vacuum tube.  The elements of a vacuum tube are as follows (Pentode shown, there are diodes, triodes and tetrodes and special types also):

   
1. Cathode (Emits Electrons)
2. Control Grid (Input to the tube, controls the flow of electrons  from the cathode to the plate, and therefore the output current at the plate)
3. Screen Grid (helps accelerate the electrons to the plate and helps reduce inter-electrode capacitance
4. Suppressor Grid (Reduces "secondary emissions")
5. Plate (The output of the tube)
6. Heater (heats cathode to emit electrons)

The following is a link to the 1933 version of the RCA Receiving Tube manual.  Reading the first section will explain how a Vacuum Tube functions:
RCA-Radiotron-manual-R-10-1933-87-pages.pdf

Resistors look like this on a schematic:
-VVVVVV-

Capacitors look like this:

--||--

Filter Chokes look like this:

   

Transformers look like this (This example is a power transformer):
   

Here is how interstage and output transformers and a speaker connect to the Power Output tubes of a radio.
   

I numbered several connections on the following cutout of the schematic of this set, which may help you find some waypoints:

   

Resistors 99, 98 and 97 are connected in series (end to end) and form a "voltage divider" between the output of the power supply and ground. 

Point A is the junction between one leg of Resistor #99, the output of the power supply choke #101, the lead to the speaker field coil and audio output transformer center tap.

Point B is the junction of the other leg of Resistor #99 and one leg of resistor #98, one leg of resistor 104 and a 1.0 uF Cap (Labeled 1) that is part of Cap # 89.

Point C is the junction of the other leg of Resistor #98, one leg of Resistor #97, a wire that leads to the screen grids of several IF, RF and converter tubes, and to a 2.0 uF Cap (Labeled 2) that is part of Cap #89.

The other leg of Resistor #97 connects to Chassis Ground (B-, C+), completing this voltage divider

Point D is the connection to one leg of the speaker field coil (an electromagnet) and the center tap of the primary of the Audio Output Transformer (The 2 "ends" of the primary connect to the plates of the 2 Audio Output tubes).  Point D connects to Point A.  The field coil and resistor #100 comprise another voltage divider.

Point E is the junction of the other leg of the speaker's field coil, one leg of a 7,750 Ohm Resistor #100, the primary of the interstage transformer, other points and a 3.0 uF cap, (Labeled 3) of Cap #89.  The other leg of the 7,750 Ohm Resistor #100 connects to chassis ground, completing that voltage divider.

Please note that almost all electrolytics used in power supplies are polarized.  For Cap #89, the negative terminals of all caps that comprise Cap #89 all go to Chassis Ground. Please note that the Chassis Ground is not the most negative part of the power supply; the center tap of the HV secondary of the Power Supply is. In this configuration, "C-" voltage comes from this point.

Please note that the negative terminals of the main filter caps, labeled 103, 104 and 104 (not a duplicate) do not go to chassis ground, they go to the center tap of the HV secondary, the most negative point on the schematic.

Hope this helps.

RE: Philco 116X cap question - Hamilton - 12-03-2025

Thank  mrFixer, I had to go out of town on a personal matter so the radio was on hold for a couple of days. 

I’ll get at installing the caps for #83 and see how that goes. Unfortunately all I have is an empty hole where that 4 part cap used to be and I hope whoever did that didn’t alter/cut out any required wiring. That is part of my problem, I can see where the required wiring is on the schematic but it’s not as simple when I’m trying to find it on the chassis. 

Thanks again and I appreciate your thorough response.

Hamilton

RE: Philco 116X cap question - Hamilton - 12-03-2025

So I placed the 4 caps where I believe they should go, I had previously changed all out of range resistors, capacitors and did the bakelite blocks. 

I fired up the radio and did have sound coming from the speaker. No stations received and my voltages were way off. All A/C voltages were good and all the following are DC measured to the chassis. I was getting 127 AC from my house outlet.

377 at the 5Z3 instead of 340
364 at both 6A3’s instead of 320 
274 at the plate and screen grid of the 42 instead of 220
55 at the plate of 76 OSC instead of 98
124 at the plate of 77 1st AF instead of 95 and 86 on the screen grid instead of 72

I got 0 DC at on the plates of the following; the 78 1st IF, 78 2nd IF, 78 RF and the 77 1st Detector
I got 80 on the above tubes on their screen grids instead of 88

All of the Kathode readings on all the tubes were fairly close to what was expected.

I’ve seen the higher voltages like I got in the first three tubes on other radios before but there are obviously some serious issues, any suggestions as to where to start would be greatly appreciated!

RE: Philco 116X cap question - vinzer - 12-03-2025

check 95 and 101 one of them might be open.

RE: Philco 116X cap question - Hamilton - 12-03-2025

Thanks Vinzer. I checked the three section candohnm and it’s at 273, 98 and 21 ohms, the field coil is 1.16K ohms and the filter choke is 86 ohms.

RE: Philco 116X cap question - Hamilton - 12-03-2025

I believe I’m back to my first post. As I mentioned the entire 4 section cap was missing when I was given it and it looks like I miswired in one or more of those 4 caps. 

It looks very simple on the schematic to find the tie-points for those 4 caps but when I look at the chassis I am somewhat lost. Where parts actually are and where they should go on the chassis, is a process that I have yet to master. 

I probably attached one or more of these caps to the wrong end of a resistor, or attached one of the wires to the wrong lug. I will trace out what I have done and see if anything pops out. 

In the meantime any suggestions are more than welcome.

RE: Philco 116X cap question - MrFixr55 - 12-04-2025

Hi Hamilton,

First off, I am not too worried about the high voltages. the radio was designed for about 115V and you are running it at 127V, that is about 10% high and may explaiin the high voltage for the plates of the 6A3s. Also, if this is a Class B amplifier, instead of a Class A amplifier, or if the 6A3s are weak, this, too can generate higher than expected voltage. I have seen that before when an audio output tube was weak.

First off, find the junction between the Field Coil and the 7750 Ohm resistor and measure. This Junction supplies B+ for all tubes except the Output tubes and Oscillator, so this must be good. It should be about 270V given your current voltage measurements.

Next check for about the same voltage on both sides of the Shadow Meter and the 2KOhm resistor that parallels it. If you found arounf 270V on one side and oV on the other side, then troubleshoot that circuit.

The common B+ for the plate voltage for the RF, 1st Detector and 1st IF passes through the shadow meter and the 2KOhm resistor in parallel with it. If this opens, then the plate voltage for these tubes is Zero, and because the screens are drawing excess current if the plates haved no voltage, the screen voltage may be low. This would have been the first place I would have you check, except that you state that the plate voltage for the 2nd IF is also Zero Volts. Check your wiring. You may also have 2 problems; an open at the shadow meter and an open at the output transformer for the 2nd IF. Troubleshoot that by measuring resistance between the 2nd IF Plate and the Audio Drover plate. It should be about 10KOhm, the value of resistor 61. If this is good but you still receive 0V at the 2nd IF Plate, then Cap #60 is shorted. You may not be able to read that short with a meter, just change the cap. If 60 is a bakelite block, then the internal connection must be broken if you just want to bridge the block.

The Candohm Resistor, #96 is all about generating bias voltages.

Hope this helps.

RE: Philco 116X cap question - radiorich - 12-04-2025

Hello Mrfixxr ,
I would not doubt it is a weak tube also I don't trust those The Candohm Resistors
Sincerely Richard

RE: Philco 116X cap question - Hamilton - 12-04-2025

I want to thank everyone, special kudos to MrFixr55, for providing guidance on how to get this radio working. 

The 2K resistor was missing and the 7750 wire wound was not connected properly to bakelite block #47. It was connected to the ground of that #47 block and the other end was grounded as well. The blue circles in the enclosed photo.

Not sure how I missed the 2K but lesson learned to be more vigilant next time. I learned a lot working on this radio, definitely be using those lessons for the next project.

By the way, the radio works very well now. Much appreciation to all!

RE: Philco 116X cap question - MrFixr55 - 12-05-2025

Hi Hamilton,

Glad I was able to help but the real congrats belong to you for taking (many) words, digging in and finding the problems.

Next step is to put a radio / aux switch in (May be in the later schematics such as the 39-116, etc.), clean everything up and when you get it just right, find another radio and fix it.

If you can, post a pic of the completed project.

Again, thanks for the mention and congrats to YOU for a successful fix!!!