Hi, this is my first radio restoration. The chassis I am working on is a Philco-90 cathedral with a single 47 audio output. I rewired the chassis and all bakelite condenser blocks re-stuffed along with new electrolytic capacitors. Resistors were checked and out of tolerance were replaced.
I powered the chassis through a variac and isolation transformer with out the tubes, all voltages are correct and at the proper locations i.e. transformer leads and filament circuits. I feel comfortable installing the tubes however I am not sure the proper procedure on safely checking the rest of the circuit. Does anyone have tips or comments where I should go from here and what to look for. Incidentally I am waiting on a shipment of a 47output tube, which is missing on the chassis.
Thank and much appreciation

I do not recommend powering up the chassis with all the other tubes in place with the output tube missing. The combination of all of the tubes causes a certain voltage drop across the field coil of the speaker. Without this voltage drop, voltage may be excessive for other tubes. It is wise with most radios to have all of the tubes in place when powering up. However, it is usually acceptable with most radios to power them up with all of the tubes removed, or with all tubes in place except the rectifier.

If you put the rectifier in, then all other tubes should be in place. In the case of your radio, you could just put the rectifier in and not the other tubes. This would tell you if your electrolytics are good or not. With all of the other tubes missing, however, unless the electrolytics are discharged slowly through about a 10K resistor, they may remain charged, which would be dangerous, should you dig around under the chassis again. When a radio is normally operated with all of its tubes in place, the still warm tubes discharge the electrolytics after the set has been turned off.

Except under certain conditions, then, you probably shouldn't power up your set with just the rectifier in place. When those conditions arise, someone on here will tell you to do that.

Once you obtain your output tube, though, put all tubes in their proper places. Slowly bring the radio up to power. Observe it at about 1/2 to 3/4 full power. See if you find any smoking components. See if a blue glow on the glass of the rectifier remains after the set has been on for more than 5 seconds. If nothing bad happens, and you see no flashing in any of the tubes, bring the set up to full power after 5 minutes. Before 5 minutes, you may want to listen to the speaker at 3/4 full power. See if there is a strong hum or if it's faint or non-existant. If faint or non-existant, see if the volume control affects anything. See if you can get stations (remember to connect an antenna to the radio). See if you can get a hum by touching the grid of the 1st audio tube. If a hum is made, then your audio section is likely functioning somewhat properly.

After the 5 minutes have gone and you've brought your set up to full power, observe all tubes and components as before. If the rectifier flashes blue or purple, turn the set off. If purple, then it is definitely gassy. If blue, this could mean a short or it could be gas in the rectifier. If the plates of the rectifier start to glow, then you definitely have a short in the radio. Otherwise if nothing bad happens, try tuning in stations. Keep the radio running for at least 15 minutes if some stations can be brought in. After this point, if nothing bad happens, then the radio is likely in fine working order. If stations are not easily received with a long straight wire suspended at least 12 feet in the air outside, then you may need to align the radio with a signal generator. Some stations should be easily received by just touching the antenna terminal with your finger. Using an indoor antenna, though, introduces all sorts of static if you use fluorescents, dimmers, computers, televisions, microwaves, wireless internet, etc.

Thomas

Hi Larry

Agree with Thomas. It's not a good idea to power your radio with a rectifier and no #47 tube. The 47 draws most of the current in your radio. Without this loading voltages will be high.

Shouldn't power your radio with only the rectifier tube. Without loading from the other tubes voltages can be 1.414 times AC input to the rectifier. This may exceed your filter cap voltage rating?

Norm

:I do not recommend powering up the chassis with all the other tubes in place with the output tube missing. The combination of all of the tubes causes a certain voltage drop across the field coil of the speaker. Without this voltage drop, voltage may be excessive for other tubes. It is wise with most radios to have all of the tubes in place when powering up. However, it is usually acceptable with most radios to power them up with all of the tubes removed, or with all tubes in place except the rectifier.
:
:If you put the rectifier in, then all other tubes should be in place. In the case of your radio, you could just put the rectifier in and not the other tubes. This would tell you if your electrolytics are good or not. With all of the other tubes missing, however, unless the electrolytics are discharged slowly through about a 10K resistor, they may remain charged, which would be dangerous, should you dig around under the chassis again. When a radio is normally operated with all of its tubes in place, the still warm tubes discharge the electrolytics after the set has been turned off.
:
:Except under certain conditions, then, you probably shouldn't power up your set with just the rectifier in place. When those conditions arise, someone on here will tell you to do that.
:
:Once you obtain your output tube, though, put all tubes in their proper places. Slowly bring the radio up to power. Observe it at about 1/2 to 3/4 full power. See if you find any smoking components. See if a blue glow on the glass of the rectifier remains after the set has been on for more than 5 seconds. If nothing bad happens, and you see no flashing in any of the tubes, bring the set up to full power after 5 minutes. Before 5 minutes, you may want to listen to the speaker at 3/4 full power. See if there is a strong hum or if it's faint or non-existant. If faint or non-existant, see if the volume control affects anything. See if you can get stations (remember to connect an antenna to the radio). See if you can get a hum by touching the grid of the 1st audio tube. If a hum is made, then your audio section is likely functioning somewhat properly.
:
:After the 5 minutes have gone and you've brought your set up to full power, observe all tubes and components as before. If the rectifier flashes blue or purple, turn the set off. If purple, then it is definitely gassy. If blue, this could mean a short or it could be gas in the rectifier. If the plates of the rectifier start to glow, then you definitely have a short in the radio. Otherwise if nothing bad happens, try tuning in stations. Keep the radio running for at least 15 minutes if some stations can be brought in. After this point, if nothing bad happens, then the radio is likely in fine working order. If stations are not easily received with a long straight wire suspended at least 12 feet in the air outside, then you may need to align the radio with a signal generator. Some stations should be easily received by just touching the antenna terminal with your finger. Using an indoor antenna, though, introduces all sorts of static if you use fluorescents, dimmers, computers, televisions, microwaves, wireless internet, etc.
:
:Thomas

Thank you Norm, I have responded to Thomas and you are welcome to read my response.

I agree with both of you and will wait for the 47 tube to arrive however I will admit this is a wonderful hobby and I can’t believe how much I am hooked.

My wife who has re-sparked my interest is responsible for starting my hobby.

Again thanks for your time and reply.

Larry

Thank you Thomas , this is good advice. I will wait until the 47 arrives hopefully by Tuesday next week, then I power the unit per your instructions.

I am an electrical technician working for a Kiln manufacture, my job is wiring control panels and testing. I have many years experience powering circuits and testing functionally and accustom to working with high voltages however knowing this radio can produce over 680 volts on the transformer has earned my respect.

I have to admit wiring the chassis was not as easy as anticipated, I took pictures and followed the schematic but keeping myself from being trapped as there are layers of wires and components to install was not easy.

I can’t believe how much enjoyment this project is giving me and I plan on keeping this Philco in the bedroom for morning news.

I will keep you posted once the 47 arrives and I start testing.

Again thanks for your time which I am very grateful.

No problem. I forgot to put in my post what Norm said. I was going to mention that part as well, which is why I said that unless it is advised, it is not a good idea to turn on a radio with just the rectifier in place. Somewhere in A.D.D. land, though, I lost track of that thought. You'll notice my A.D.D. because my posts tend to wander around a bit.

Good luck with the Philco. Most older Philcos are a nightmare regarding wiring. There were plenty of sets produced in the 1920s with very neat and orderly wiring, and there were plenty of sets produced in the 1930s and 1940s with orderly wiring. Philco didn't seem to have this down yet in the early 1930s. Actually a lot of radio manufacturers used rather random wiring techniques in the 1930s. By the 1950s, however, it was realized that high fidelity could not be achieved without orderly wiring.

Good luck, too, with AM reception. I have many beautiful radios which have nothing worth listening to.

Thomas

:Thank you Thomas , this is good advice. I will wait until the 47 arrives hopefully by Tuesday next week, then I power the unit per your instructions.
:
:I am an electrical technician working for a Kiln manufacture, my job is wiring control panels and testing. I have many years experience powering circuits and testing functionally and accustom to working with high voltages however knowing this radio can produce over 680 volts on the transformer has earned my respect.
:
:I have to admit wiring the chassis was not as easy as anticipated, I took pictures and followed the schematic but keeping myself from being trapped as there are layers of wires and components to install was not easy.
:
:I can’t believe how much enjoyment this project is giving me and I plan on keeping this Philco in the bedroom for morning news.
:
:I will keep you posted once the 47 arrives and I start testing.
:
:Again thanks for your time which I am very grateful.
:

Thanks Thomas,
I read some ware in a post that it was important when replacing a wire or component to put things back where you found them. I am not sure why except maybe for RF interference or the potential of changing the characteristic of a tuned circuit.

In my re-wire I kept that in mind however in cleaning the chassis and components I am almost positive I have altered the original alignment setting.

One thought I pondered on during the rewire was what it would have been like back in the early thirties assembling one of these sets and what tools were available. The other thought was once a bare chassis hit the floor how long it would have taken for a complete assembly.

Congratulations on your first restoration Larry. I hope all goes well and keep us posted on your progress.

In conjunction with what Thomas and Norm said, you may also want to monitor the B+ while powering up your set. The volt meter should be connected from the rectifier output to the center tap of the power transformer. This connection may be easier to make across the first electrolytic, which is what we are really wanting to monitor.

As you advance your variac, watch for the first sign of B+, then immediately halt the advancement, or maybe even back off a bit. If this is done early enough, you should see the B+ slowly rise as the electrolytic condensers charge and the rectifier filament continues to warm up. A steady rise is a good indication that your set is not drawing too much current. If you do not see the rise, be careful with further increases. At this point, a direct short in the set is not likely to hurt anything, but if you get wild enough with advancements, it could.

Once the B+ is steady, advance your variac somewhat and you should see an increase almost immediately. If it doesn’t, this may be a good time to shut down and look for problems. If all looks well, continue the advancement as long as the B+ rises with it. At some point early in this game, the other tubes will be warming up enough to draw current, so the voltage increase may not be exactly steady. While this is happening, you may hear your set coming alive. However, if the B+ actually begins a steady decline during this time, shut the set down. Many radios work fairly well at about 80 VAC or less, and you may actually know exactly when you are raising your set from the dead. It’s a real good feeling when this happens on the first try from a complete rebuild.

As you approach line voltage with your variac, it will be easy to see if the B+ stays below the voltage rating of the electrolytics, but you also need to check them for surge voltage. This voltage often happens during warm up, and should be checked after the set cools down. Then watch the B+ rise again during this warm up. Before the other tubes begin drawing current, the B+ may surge above normal, then drop back. Of course, the surge should also be below the voltage rating of the electrolytics.

Thanks Billy,
This is most helpful and I will keep you posted once I receive the #47 output tube.

Noting wiring: Bothering the wiring in your Philco isn't that critical. With these radios, your only trouble is placing the grid wires from one stage too close to the plate wires of another. This will cause feedback.

Where wiring placement is critical is in the Foreign band (short wave from about 6.0 MC to 30 MC) and in the FM band. Sometimes moving the wires around can shift stations around just a bit. Some radio manufacturers actually use this for part of the alignment procedure. Some may tell you to move a condenser or coil slightly to align one end of the dial. In this case a trimmer device may not be provided.

Thomas

Thanks Thomas,
This information is very useful as my next project will be a short-wave receiver.
Larry

First of all I want to thank every one on the wonderful advice I have received, once again thanks.

I am not sure where to begin except I am extremely happy with this project and somewhat surprised the radio came alive even allowing me to tune in a station.

It was not my initial intension to completely rebuild the chassis, but to go in and see if I could repair the set and come back later after I proved myself for a complete restore, however wanting to make the chassis look new again got the better of me. I removed every component for cleaning including the tuning condenser & trimmers. I pretty much figured after assembly and initial testing I would find something I should not have done but so far everything seems fine.

I did wait until the 47 out-put came in before powering the set and followed both Thomas’s & Billy’s instructions. Here is what I saw as I incremented the variac 5 volts at a time taking DC readings across the 80’s out-put and center tap.

AC Voltage in DC Voltage out
5.0 0.000
10.0 0.000
15.0 0.000
20.0 0.000
25.0 0.024
30.0 0.178
35.0 0.939
40.0 2.760
45.0 5.530
50.0 7.953
55.0 11.10
60.0 14.15
65.0 19.63
70.0 25.45
75.0 38.02
80.0 55.01
85.0 67.83
90.0 118.5
95.0 162.7
100.0 203.2
105.0 235.2
110.0 260.1
115.0 276.9
120.0 292.2

The 80 rectifier did not show any blue or purple haze or flash and all tubes showed no signs of flashing.

Very good. Be very careful when reassembling the radio. www.tubesandmore.com sells cloth wire, should you need any, though your original wire should be fine.

Also, regarding blue flashes in rectifiers, if you turn your set on normally (without a variac), you will likely see a small blue glow right next to the plates in the rectifier when the set is first turned on. This will last a second or two. This is simply the rectifier being slightly overloaded (if you want to call it that) when the electrolytics are being charged up. In most sets, after this has happened, you won't see a blue glow here anymore. It is somewhat common to see a small steady blue glow in some output tubes of some radios. Some RF tubes which handle a medium amount of power may glow blue in small places, too. I even have a portable battery operated radio in which both the oscillator tube and the output tube have a small trace of blue glow (you can't see this unless you're in a dark room).

Purple glow in a tube almost always meens gas, however. This is not good unless the tube is designed to have gas in it (thyratron or gas rectifier).

Thomas

Thanks Thomas I will try that. There’s a lot I don’t know and any information helps me to be aware and slowly understand this hobby.

I am currently studying the basic concepts of alignment and slowly getting the concept of why and how the procedure is preformed. Hopefully tomorrow I will be ready to try and will keep you posted on my progress.

Larry