[jcassity]

just checked,, apparently i have zero spares of the 6J5 ,, which with zero mods is compatible with 6C5.

~all according to sylvania cross ref tech guide i have

[Joeztech]

Today I finished replacing the electrolytic sections in both can electrolytic capacitors in the power supply. There were two, a small one P/N 30-2570 which consisted of two sections tied together, a 25uF@450V and a 10uF@450V with a 10K 2W resistor going back to the triangle section a 10uF@450V of the large can, P/N 30-2556, and a Philco Power resistor P/N 33-1336-51 from the small can to the 25uF@450V half-round section of the large can, P/N 30-2556. When I was removing the large can electrolytic I discovered that its ground twist-tabs were never soldered at the factory. Not a single twist tab of the large electrloytic had been soldered to ground. I made sure that one of them was soldered to the chassis this time. It may not have caused a problem, but better safe than sorry.

Next come the replacing of all the paper-wax-foil capacitors in the set. some are in tight spots, but nothing looks too difficult.

Joe

[Joeztech]

Philco used a number of .006 paper-wax-foil capacitors in these radios. They are in the audio circuitry used as coupling capacitors. I decided to replace these with .01@630V capacitors instead of ordering .0062 capacitors. I reached a stopping point late today and will do more tomorrow. I noticed that the terminal strips have solder lugs that are made for simple wrapping rather than feeding leads through a hole in the lug and then wrapping. This actually makes replacing parts easier. It likely made assembly at the factory easier also.

The schematic that seems closest to this radio is a Beitman's schematic. Their schematic shows the deleted B+ Choke and a simple resistor substituted for the choke. The value may vary depending on the production run. This one looks to be about 1.2K ohms and around a 6 watt resistor (which could be less than 6W).

Joe

[morzh]

If it is the coupling cap to the phase inverter and the two after it to the pushpull, I would rather keep it 6nF. It will work but still....

[Joeztech]

This morning I discovered that the R102 300 ohm resistor between the 5Y3 cathode and the input capacitor is completely open. It showed signs of having been very hot - any markings on the outside of the resistor are completely burned away. I note that the original Code 121 version was passing about 92mA through the field coil choke (dropped 60VDC and had a DC resistance of 650 ohms). I assume that this Code 125 version power supply has to pass about the same overall DC current so that would say that the R102 would dissipate about 28 Watts! That seems rather high and the original resistor does not look to be any more than about 10W in size.

According to the original Code 121 information the DC volts at the cathode of the 5Y3 is about +300VDC and that is based on having one 20uF electrolytic section at that point before it goes through the field coil choke. The Code 125 version I have has the R102 300 ohm resistor ahead of any electrolytic section and the first electrolytic capacitance it sees is about 35uF with the usual tolerance. So that means that R102 has to absorb some AC energy as well as the DC drop across it.

Any suggestions?

Joe

[Radioroslyn]

My calculations come up w/ 300 ohms @ 92ma = a 28v drop @ 2.6w.

[Joeztech]

Oops - I slipped a decimal place! Thanks for rechecking me on that. I did not want to order a huge resistor. The OEM resistor looked like it could have been a 3W or perhaps a 5W resistor. It is a dogbone style resistor and since all markings were burned off no ratings information was at hand. All of the rest of the resistors showing up in the data for a Code 125 seem to be OK. Now I can safely order the correct value and wattage rating for the radio and continue.

I had spent time for a few days ahead of working on this radio to document some items about a Fisher MF-300 FM stereo tuner with search-tune and their RK-20 remote control. Today I received a copy of the owner's manual and service manual for the MF-300. Unfortunately the RK-20 information I do not have at this time. I will probably have to trace it out manually and create a schematic and parts list for it. The MF-300 and the wireless RK-20 remote are rare. Until now I had not found any source of documents for it. I will be scanning the documents and submitting them to the AudioKarma database under Fisher documentation.

Have a great day everyone!

Joe

[Radioroslyn]

I'd go w/ a 7-10w unit.

[Joeztech]

Radioroslyn;

I will check on the physical dimensions of the various wattage units. As long as a 10W  will fit OK I may go with that. I am not seeing any indication that any severe short ever took place in this radio, so I think the OEM resistor just failed from long term heat and ageing issues. One 40uF electrolytic had been tacked into circuit many years ago and it does not appear that any other parts were replaced.

So far among the resistors I have checked I am seeing some that are out of tolerance in an increased value direction, but as a surprise, some appear right on the money. Many of the resistors in this set are 20% tolerance types.

Joe

[jcassity]

R102 300 ohm resistor

i recommend reading through my thread. .... it will save you time.


post 176,, your gut feeling is correct as was mine.  go with something you can relocate to the top side of the chassis where the tubes are.
R102 willl end up being calibrated to your radio but i found 600 ohms and 50 watts or more was needed to get the voltage at both 6k6's below 300v each **and** be able to let out the heat its going to generate..
I would be very interested if you were able to make a 10w 300ohm resistor work in this area.


post 160 is where i decided tto change to what was best.
post 127 shows that this R102 is directly underneath your 5y3,,, not a good place for such a "known issue" problem resistor.

your talking about a mix of AC & DC at this point in the circuit is correct. This is the resistor philco never "solved" and it was the one that was a "known issue".
http://philcoradio.com/phorum/showthread...97&page=12

big things i noticed and worked hard on....
-R102- many many hours solving this "known" problem that was never factory fixed for real.
-the filter caps downstream of the transformer but upstream of the 5y3 are incorrectly identified on the fold out schematic but once you red line this you will be fine.


asked earlier,,, what run number are you?  i assume run3.

there are no known diagrams of run3.

if you got prints from the philco workbench you will discover that ****************ONLY *********** the fold out schematic should be used to restore a run3 code 125. 
You have to combine Run1 and Run2 and Run3 ..
The diagrams from Chuck "philco work bench" will define all runs,, run1, run2 and run3.
when you bounce from each you will find out what i am saying.

f you have many question markes in your mind about the things you find odd,, this fold out schematic will help.

avoid using the schematics that are formed into a booklet so to speak.  those dont match a run3 code 125.

im at 304 772 3411 if you need to sanity check anything.

hopefully you are running a 7af7 on V1, if not you will smoke a replacement resistor you prob did on V1.... I did.
also my v1 was carbon flashed so before i had any locktal sockets, i took it apart , sanded the bakealite , flipped it over,,, did corrosion control on the pin then put it all back together. wish i had smaller rivits though, the oem ones were perfect and low profile.

[jcassity]

also, if interested........

with a paint marker i wiped on a white layer then wrote on each part what thier schematic designation was on each item.

the white paint in the future will discolor when a future fault happens. this will give you the ability to have a visual indication of where the failure is in the future. the paint will turn brown

[jcassity]

actually, i just looked....

a started the battle with R102 on post 31.

over a 100 posts later and it got solved.

[Joeztech]

Jcassity;

Thanks for responding. You put a lot of work into your 46-1226 radio. I am glad you managed to get it working well again.

I have been reading your posts on your Code 125, and one thing that can be done to solve the AC + DC energy on R102 is to add an extra electrolytic capacitor right at the 5Y3 cathode. That filters the pulsating one-polarity AC pulses into DC with some ripple. That pretty much removes the AC energy from the equation at the beginning. Then the following stages can deal with just final filtering and bypassing. I believe you determined that the power transformer in your set had been changed. When power transformers are changed it is easy to wind up with additional problems if the replacement is not made to the original specifications of the manufacturer. I think that is one of the issues that caused you such grief in dealing with R102.  My initial checks of the Philco OEM transformer in this set show it to be OK, so I likely will not have as much of a problem to deal with as you did on your set.

I will check the AC voltage to the plates of the 5Y3 and report back on what I measure there. If the original transformer design was not higher than required, there should not be that much of an issue to deal with as to the wattage rating of R102. After all, the radio I am working on had its R102 for many years before it finally failed.

On this radio, if the voltages measured at the screen grids and plates of the audio output tubes is correct it says that the power supply of the set is delivering about 92mA to the entire set through its B+ distribution. A 7-10 Watt R102 should be able to handle that without too much issue. Even a lesser wattage resistor might well be OK.

Joe

[jcassity]

Ill watch you,, then I will copy your method after you test.
I see what your saying though.

im thinking you are going to bond that cap from the cathode to chassis,, to get rid of the ripple ac.

[jcassity]

joe,
was hoping to see the solve soon on that resistor issue , and progress pics