[mikeyg]

First time posting here. I have been very lucky over the past couple of years trying to work on various tube radios. I just received a philco 41-287 from a family member and started working on it. I replaced all wax and electrolytic caps and powered up the radio. Everything seemed good for about 15 minutes but I noticed the volume seemed a little bit low. While tuning in stations I heard several loud pops of static and now I have no sound, not even static. I don’t want this thing to beat me it’s the first large console I have worked on. Can I get some direction on what to check and what it might be? I am fairly new to this and still learning. Need any help to be dumbed down for a newbie, like for a third grader. Thanks in advance

[klondike98]

Welcome to the Phorum!


I'm not the best troubleshooter so I'll leave that to some of the folks that are pretty good at it.

[Vlad95]

The symptoms listed do not indicate a specific problem.

First:
check all components for external heat, combustion, and smoke.
If you find any faults, please report them here.

Second:
measure all the listed voltages according to the diagram.
If you find any voltage deviations of more than 20%, please report them here.

Third:
wait for any possible recommendations on the forum.

Good luck

[RodB]

Hello Mikeyg and welcome to the Phorum.

Here's a link to the schematic for your radio:
https://philcoradio.com/library/download...20Book.pdf

You'll want to attempt to isolate the problem between power supply, radio circuits and audio circuits. Start by checking the B+ voltages at the power supply output. If the voltages are OK then measure the plate voltages of each tube. If these are OK then touch the center terminal of the volume control with a screwdriver. You should hear a hum from the speaker. If no hum, then there could be a problem in the audio section. If you hear a hum then there's likely something wrong in the rf circuits. See what you can determine from this.

[KCMike]

Hello and welcome.
Besides the above suggestions you might try wiggling the tubes
the locktal tubes are bad about not getting good connection to the sockets. Sometimes its good to clean the pins and sockets.
Also make sure to clean the band switch.
Hope this helps.

[mikeyg]

So took a look at it and I don’t see anything obvious. I also touched a screwdriver to the middle post of my volume control which has a .01 cap and nothing. Last night it was playing ok just not as loud as I think it should when it just stopped. All the tubes are lit some just barely but exactly like they were last night. I will have to get a set of needle Leeds before I try poking around in this thing to check voltage though. Do I go negative to case when I do that? Thanks for the schematic. The one I had was super hard to read. Any idea where I should start when checking the voltage?

[Arran]

Given the era this was built I would check the primary of the audio output transformer, I would also check the plat load resistor of the first audio tube for either being open or greatly increasing in resistance, though the latter problem I haven't encountered in a Philco. These sets had the audio output transformer mounted to the chassis, and whilst that wasn't an issue in itself, for some reason the transformers have a high failure rate. I'm not an engineer but I have wondered before whether it has something to do with the "screen gid inversion" setup they used in the audio output stage, whilst this set has a ninth tube that they are only using it as a detector, not a phase invertor, so it's basically a 41-280 with a tube stuffed chassis.
Regards
Arran

[mikeyg]

Ok so I checked resistance between the wires on the output transformer with it still attached to everything and got nothing. When I get home this evening I will de solder the wires so I can get a better check on it. If it’s bad what can I replace it with? I would assume there is an equivalent somewhere.

[mikeyg]

In threads on a philco 41-280 I saw where it was recommended to use a p-t291 output transformer in place of the original if it is bad. If I have to go this route and it kinda seems like I might how do I wire in this new one?

[RodB]

No need to unsolder the wires of the transformer primary. There should be a 0.002 mfd cap connected to pin 2 of each 41 output tube but that shouldn't interfere with the resistance measurement. If you want to verify that the primary is open you can remove the two 41 output tubes and measure between pin 2 of each socket. If you measure around 350 ohms then it's good, if you measure an open circuit then the primary is open. If it's open, you may get lucky and find one of the transformer primary leads has separated from the transformer winding wire. To check this you have to remove the transformer, open the transformer metal shell and carefully cut the paper covering layers till the primary wires are exposed.

You should try to find out why the primary is open. It's usually one of two things. Either the grid bias of the output tubes is wrong causing them to conduct too much current or the transformer winding failed from old age/corrosion. The grid bias on each 41 tube at pin 4 should be around -25 volts. If this is OK then it's a good chance the transformer winding is defective. One other cause may be the B+ is too high. I'm assuming you monitored B+ when you first powered up the radio.

[mikeyg]

I didn’t. I’m not super versed in these. I have gotten very lucky over the years mostly with aa5 ‘s and with a philco chairside that I picked up. I have been replacing caps and cords and checking tubes but beyond that I have been kind of at a loss. I traced the three wires coming out of the output transformer and everything read open no continuity between any of the wires. I’m trying to learn more on each of these I work on. Can you point out the spot I should check my b+ voltage at? And maybe what it should be.

Also if the transformer just went out due to age can I use this p-t291 from amplified parts? I saw it recommended on a post about a 41-280. Not sure exactly how to wire it in.

[RodB]

For the P-T291 you'll be using the brown and blue wires for the plate of each 41 tube, pin 2. The red wire is center tap and goes to B+. I assume you have a 4 ohm speaker so you will use C and 1 for the speaker connection. C will go to ground. Your speaker has a hum bucking coil connected in series with the voice coil and this connection must be maintained as it was originally.

I am concerned that both windings of your current transformer primary are open. This is highly unusual to have both sides go at the same time. You must be cautious with powering up the radio after you install the new transformer. In the least you should use a dim bulb until you get proper voltage readings, especially the grid bias voltages.

The schematic shows 265 volts at the cathode of the 84 tube and 180 volts at the junction of the field coil and the 16 mfd filter capacitor. This is B+ and it should be slightly higher, maybe 10%. You can also measure it at the screen grids of the 41 tubes. It's a good exercise to follow along using the schematic so you become familiar with the various locations and parts we discuss. As a quiz, I want you to locate in the schematic, the hum bucking coil in the speaker.

[mikeyg]

Ok b+ at where the positive of the filter caps goes is reading 196v. I also have 200v where the white and black wire from the audio transformer connects to the 41 tube. I have zero volts on the other 41 tube where it ties into a cap. Physically looking at this on the 41 tube that I do get voltage on counter clockwise from it there is another wire that goes to the output transformer that has zero volts on it. Does that clarify anything at all.

[RodB]

It doesn't help much when you don't provide pin numbers or component values. When you say "I have zero volts on the other 41 tube where it ties into a cap." What's the value of the cap or what pin number on the tube socket?

Let's regroup. Maybe you can see a black wire on one 41 and a white wire on the other 41 that both go to the output transformer. Measure the voltage where they connect to the tube pins.

[mikeyg]

Sorry. I did measure it where they connect at the tube socket. I have 200v where the white and black wire meets one 41 tube. The other 41 tube where cap 57 connects with the black wire from the output transformer has 0 volts.