philco pt2 - Printable Version
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philco pt2 - wally73 - 02-25-2016
Gentlemen,
I recently acquired and old 1941 Philco PT2 radio. I have changed out all the caps and all the tubes are good . The speaker is good but when I turn it on I get absolutely no sound. Does anybody have any ideas as to what could be wrong and what I should check first? Thanks for your help.
Wally 73
RE: philco pt2 - TV MAN - 02-25-2016
Hi Wally! I am sure a few others will chime in here. I don't know how much experience you have or what test equipment you have. Looks like an ac/dc radio. I would start by a couple of quick checks. First, since this is probably an ac/dc set, you will have to be very careful if you don't have an isolation transformer. One side of the chassis will be connected to the ac line. You could get a nasty shock. That aside, with the radio on and the underneath of the chassis accessible, a good place to start is to touch the volume control lugs with your meter probe tip and listen for a loud hum or static from the speaker. If you get a loud hum, then you have a live radio and you will have to go deeper into troubleshooting. If you don't get anything, check for B+ off the cathode of the rectifier tube. Should be 120-150 DC, chassis ground volts unless it uses a doubler, then it will be over 200v. I don't have a diagram handy on your radio, but these are a couple of quick checks you can make to get an idea of what is going on. There is a lot of knowledge in here, so am sure any of us can help you through this and get your radio playing again!
RE: philco pt2 - TV MAN - 02-25-2016
Ok, I found a diagram on the radio. It is an ac/dc set. Do the check I recommended with the volume control. If nothing , check for B+. I do see a speaker field coil which could be open. You can check for B+ on both sides of the coil. Measure with your - probe on the - (neg) side of your filter caps. Make these checks and get back to us. This will give us an idea of what's going on inside there (or not).
RE: philco pt2 - klondike98 - 02-25-2016
For those who may be able to help here is the Nostalgiaair schematic and a better one on Audiophool.
You said the tubes are good but do you see the filaments glowing. They are in series so if you have one bad filament or one bad pin connection they will all be out. That will stop things from the get-go.
RE: philco pt2 - wally73 - 02-26-2016
Dear experts, thanks for the suggestions.
I am kinda new at this. The only test equipment I have is a volt/ohm meter. I checked that all the tube filaments are glowing as well as the dial light. I tried touching the lugs on the volume control . No sound or hum. Next I tried checking for DC voltage on the cathode of the 35Z3 rectifier tube. Not knowing exactly which pin was the cathode I tried them all one at a time to chassis ground . I got no voltage at all. Where do I go from here?
I await your answer. thanks
wally73
RE: philco pt2 - wally73 - 02-26-2016
HI its Wally 73 again. OK I made a mistake about the voltage. Apparently I had a bad volt meter. There are 4 wires coming off the speaker :two from the transformer on top of the speaker and two from the coil on back of the speaker. When I measure from the negative side of the filter capacitors to any one of those wires I get approx. 150 volts DC. I hope this helps.
walt
RE: philco pt2 - Radioroslyn - 02-27-2016
Hey Wally,
Measure the DC voltage from the off/on switch - and + pin 3 of the 50L6. Do the same with pin 4 and then pin 8 of the 50L6. It's a little telling that you have 150v at the filters, tell me that the power supply isn't loaded or little or no current is drawn. Voltage should be closer to 100vdc. If all is well p3&4 should be about 100vdc 8 about 8vdc.
GL
Terry
RE: philco pt2 - Arran - 02-27-2016
With most, if not all, Philco AC/DC sets the chassis and B- are isolated from each other so you can't use the chassis as a reference point for voltage measurements, you use the AC switch on the back of the volume control. In any even something is definitely not right if you are measuring 150 VDC from the cathode of the 35Z3 tube, it could be an open field coil or a dead resistor in series with the B+.
Regards
Arran
RE: philco pt2 - TV MAN - 02-27-2016
Wally, do you have a tube book? If not, might be a good idea to get one. On your 35Z3, pins 1&8 are your heater (H), pin 2 is your plate (P) , pin 7 is your cathode (k). Numbers run clockwise looking at the bottom of your chassis, starting at the locating pin or gap with miniature tubes.
On your 50L6, 2&7 are your heater, 3 is P, 4 is G2 (screen grid), 5 is G1 (signal/control grid) an 8 is your cathode/suppressor.
I agree, it doesn't sound like you are drawing any current. Have you checked voltage on both your filter caps 262 and 266? You should have B+ on both. Next, go to your 50L6 plate pin 3 to with - probe to filter cap neg (or power switch). What do you have? Also check the G2 pin 4. You should show 85 and 95v dc. If so, touch your pin 5 of the 50L6 with your probe and see if you get any static or hum. Also keep in mind this radio uses some loctal tubes and there could be some connection problems. Let us know what you find.
RE: philco pt2 - wally73 - 02-27-2016
Yeah !!! Hey guys its WORKING !!!!
I found a bad solder joint at the off/on volume control and the 7C6 tube had gone bad. Luckily I had another one to replace it. I hooked up the loop antenna from another radio to the pT2 since I don't have an antenna for it. It sounds kind of tinny with high treble but I can get several local stations on it . But I guess you can't expect too much from a 75 year old speaker that's been patched a few times. No telling when was the last time it actually worked. Anyway, its always a thrill to hear an old relic like this come back to life. Thanks for all your help . You are a great bunch of experts.
wally73
RE: philco pt2 - klondike98 - 02-27-2016
congrats!
