[ascion90]

Hello everybody 

I am a new real fan of the forum and I just started this new adventure with the Vintage tube Radios. I found a 42-327 radio and thanks to the multiple suggestions on this forum I started from the Electrolytic Capacitor. I didn't find  2oUF and I used the 33uF 450V.

The cabling was very bad a lot of "burnt" plastic wire and I changed most of them together with all the old capacitors ( except the 0.2Uf with the coil) and 4  bad resistances.
I am focusing now on the XXD Tube and broadcast band and when I checked the voltage on the tube I have between the chassis and pin 3 40 VDC ( after 10 second become 35) and on pin 6 55 VDC. But what happened was also that touching only the pin 4 with the tester cable the broadcast reception work with not a clear reception but with multiple stations. As soon as I disconnect the cable the radio come back to a white noise.

I checked the mica capacitor on pin 4 and was ok ( there is already installed a 100pF not a 50pF as in the schematic ) . I tried it with a dmm and it is 100pF and I tried in any case to change with a new one,but the only result was that touching with the "famous" tester cable the reception became bad.  I put in place again the old one and the situation is stable as the beginning. THe receptions is ok only when I touch with a cable the pin 4 of the XXD. I checked and changed the bad resistor 12 and 11 and verified the resistor 25.

I also checked the voltage between pin 7 and pin 8 and it is 3.4 VDC. but between pin 1 and pin 2 only millivolts. Is it normal? What other measure can I do on the tube? Resistance and voltage?

I checked all the contacts on the Tube pins with cleaner and sands paper and on the socket and on soldered pin. I ordered a new 14AF NOS tube because I didn't find an XXD one. I will receive it the end of next week.

Last but not least unfortunately my tools are only a DMM and a soldier what I can try more?

Thanks

[RodB]

Hi and welcome to the forum. Your voltage readings seem to be off. Be sure to have the negative side of your meter connected to B- and not the chassis. A convenient location would be at the negative side of the power supply filter capacitor. The voltage at the junction of 20 and 22, two 10K resistors, should be around 85 volts. Also, when you touch your probe to the grid you are effectively attaching an antenna to the grid, so you will hear radio stations.

Rod

[ascion90]

Hi Rod,

thank you so much for the fast feedbacks.

I tried again between a B- at the electrolytic and pin 3 of the XXD and I have 56 VDC and B- and pin 6 XXD 84 VDC.

Do you mean resistor 22 and 26 ? I am sorry I am not and expert and following the schematic and the connections into the radio I think I found the point you mention after the first 10K resistor that is connected on one side to pin 6 of 35z3GT ( 100 Volts ) and the other side to pin 3 ( 84.3Volts) of the 35x3GT together with the capacitor .01UF that is connected to pin 7  ( 3.5 Volts) of the XXD

Thank you so much for your help

CAmillo

[RodB]

You are correct on the 10K resistor, it is part 26 not 20. My diagram is a little fuzzy. So now I see a couple problems. First, the B+ is high, probably due to the increased filter capacitor value and higher modern day line voltage. You can probably tackle that later with 22mfd caps instead of the 33. Second, the plate voltage at pin 3 of the XXD should be around 70 volts given the higher B+ but it still should oscillate. The value of 26 might be too high, use your dmm to measure the resistance.

It looks like the oscillator starts running when you touch pin 4 with the probe. This suggests that a capacitor in the XXD oscillator triode is out of tolerance or the triode is bad. It could also be a bad pin connection so you might want to re-check the pins of the tube. The loctal tubes are noted for pin corrosion. I use steel wool then clean with alcohol. Don't use water on loctal tubes, it removes the lettering on the glass.

[Radioroslyn]

This one is pretty good.
https://philcoradio.com/library/download...20Book.pdf
> I use steel wool then clean with alcohol.
A little scary as the steel wool can easily leave steel wire fragment which can cause shorts.
Better choice would be fine grade (400 grit or finer) or I like Scotch Brite pads. No metallic
particles to create problems. No motor driven tools to clean or buff. These can vibrate the
internal elements destroy filaments and such.

I could go for a belt or two after working on a '42 set too!

[RodB]

Yes, that's the same schematic as I have only much clearer, thanks. Why didn't Philco put in the tube pin numbers? The scotchbrite pads would be much better, I've always worried about the steel wool fibers.

[Radioroslyn]

>Why didn't Philco put in the tube pin numbers?

Presuming you mean on the diagrams. Best guess is that is service information was printed for Philco authorized service centers. The guys therein worked these and other Philco sets day in and day out to make a living. After you see a few of them you can look at the bottom of the socket and tell what pin is what.
70 or 80 yrs later as hobbyist we look at these chassis and try and figure what's what Especially on the Phorum as we don't have it sitting on our bench but is hundreds or thousands of miles away on someone else's bench. Pics are ok but a lot of the time the don't tell the whole story to try to ascertain which pin goes where.

[ascion90]

Hi Rod 

during the weekend I will work on the radio, starting from the suggestions  on the XXD Capacitors. I already cleaned the Tube pins and the socket contacts.

Thanks to the new schematics from Terry some connections are more clear now and I will verify again all the voltages. The 26 resistor is 10.3K with the DMM like the 22. I am waiting to order the 22uf capacitor, maybe I need to change also other mica capacitors

Thanks

CAmillo

[ascion90]

Hi,

I studied the new schematic and first of all I learned that this radio is a dual band : broadcast and SW and the other position of the band selector is to enable the external Pad stations.

Starting from the end The radio now is working pretty well on Broadcast, but not at all on SW. I changed the two capacitors number 5 and 10. I had some trouble because on the schematic the number 10 is 50pF and installed there was 100pF and the number 5 on schematic is 5pF but installed and 80pF. Is it possible an error on the schematic for the 5pF ?

The radio seems to be repaired many years ago with old component, but newer than the other. The radio finally worked on broadcast changing them with two mica capacitors of 50pF each.

But I have a lot of doubts about the voltages and a question : why the radio started to work on Broadcast when I changed capacitors on the SW Aerial Transformer? At least this is what I understood with my limited competences looking at the schematic

Starting from the Voltages these are my readings from B- (the electrolytic  negative Pin) for each measure:

35Z3GY PIN 7 132.9 VDC

50L6GT Pin 4 99.7 VDC Pin 3 87.6 VDC
7C6 PIN 2 62.9 VDC ( The schematics says 28vdc)
7B7 PIN 3 60 VDC PIN 2 98.7
7B7 PIN 3 60 VDC PIN 2 98.7

XXD PIN 3 Starts at 71 VDC and stabilize at 56 VDC  Pin 6 83 VDC

I also verified again the two 10K resistors 22 and 26 with the DMM and they are ok. The voltage and is 99.8 VDC between the two and became 56 VDC after the resistor 22 . I also tried just to see what happens to change the resistor 22 with an 8K and a 2.2K ohm . The voltage on pin 3 increase. I installed again the original 10K resistor checking again the resistance and the voltage.

Next week will arrive the 22 uF Electrolytic and a new 4.7M ohm 2W resistor I used temporary a 0.7W. I will try to verify again the voltages

I didn't discovered why the voltage is so high on the 7C6 ( 63V Vs. 28V) any idea?

What do you suggest to start troubleshoot the SW band?

Thanks

Camillo

[simplex1040]

If you haven't  already,  clean the band switch this cures lots of ills on multi band Philcos

[RodB]

Excellent progeess. High plate voltage on the 7C6 triode may be a bad 36 resistor, s/b 470K. Also low current flow in the triode.

SW band oscillator probably isn't running. Check coil 18 for continuity pins 1 to 3 and caps 14 and 9.
Could be switch contacts too.

I'm hoping the new power supply caps bring the B+ down. You may have to insert a dropping resistor to take it down.

BTW - capacitor 21 with the choke coil wrapped around you can replace it with or without the coil.

Rod

[Radioroslyn]

>a new 4.7M ohm 2W resistor I used temporary a 0.7W.
If you are speaking of #34 there is very little current flow thru this resistor.
An 1/8 w would be fine too.

[RodB]

Correction on the ocillator coil. It's part 19 for the SW band. Measure between terminal 4 and 6 for continuity.

[ascion90]

Hi Rod

Before changing the Electrolytic Capacitors I checked the resistor 36 and it is ok. I changed the capacitor 21 without coil.

I checked the continuity on the Oscillator pin 4-6 and unfortunately there is not continuity!!! This is the problem on Band SW right?

Do you know where I can find a new one with the right specifications? I tried to soldering the pins but no Continuity...

Regarding the Electrolytic capacitors I changed it with 22UF but the Voltages are more or less the same with the 33uF for all the points I checked before.

The radio works fine can the high voltage create damages on the radio?

I didn't change the resistor 34 following the RadioRoslyn suggestion 

The radio on the broadcast frequency works fine , but there is a noise frequency when I switch on my soldering tool ( I spent a lot of time to discover). Can be the Coil on the Capacitor 21 that I removed? Or some ground not well soldered?

Thank you so much for all the information and great suggestions. I don't know if it is simple to find a new Oscillator and probably because I changed also some mica capacitors I need to make the Alignment but I don't have tools to do it. Are they expensive?

Thanks

CAmillo

[Radioroslyn]

>I checked the continuity on the Oscillator pin 4-6 and unfortunately there is not continuity!!!

So the next step to do would be to measure the resistance from pins 4 to 5 then 5 to 3 then 3 to 6. All should measure a near dead short. This will determine which section has the fault. If you are lucky the winding will be one layer wound flat onto the form so spotting the problem will be easier than if it was several layers on top of one another. Also the SW winding is somewhat smaller (less turns) than the the bc band. The bc band would be around 90 turns and your sw band would be about 30 turns.
The faults would be a break the wire or a green dot indicating rot.

Happy Hunting!