The PHILCO Phorum
Trouble getting started - Printable Version

+- The PHILCO Phorum (https://philcoradio.com/phorum)
+-- Forum: Philco Radio Discussions (https://philcoradio.com/phorum/forumdisplay.php?fid=5)
+--- Forum: Philco Home Radios (https://philcoradio.com/phorum/forumdisplay.php?fid=6)
+--- Thread: Trouble getting started (/showthread.php?tid=5200)

Pages: 1 2

Trouble getting started - Eric Adams - 09-17-2012

Hi guys,

I'm working on my first. It is a 48-200. Simple, right? Got it with a loud hum and did a recap. Hum is gone but no sound. I have 2 schematics from different companies and they each list tubes but one shows a 35Y4 and the other shows a 35Z5GT. Also one shows a 50L6GT, the other shows a 50A5. (mine has the 2nd ones). The sticker on the bottom of the case shows the ones that are in the radio. Anyone ever run into this?

Thanks.

RE: Trouble getting started - Arran - 09-17-2012

Find out what code number the 48-200 is, it will be something like Code 121 or Code 122, possibly with a run number like #1 or #2 as well, this will tell you which chassis you are working on. As to why there is no sound it could be as simple as a bad tube, it could be an open plate resistor, or even an open primary on the output transformer. Try touching the center lug on the volume control with a screwdriver and see if a hum comes out of the speaker, also try touching the grid pin of the power output tube, there should be a capacitor running between this tube and the 1st audio tube. It's time to break out the volt meter and check the plate and screen voltages on the 1st audio and power output tubes. If the audio section isn't the problem it's time to look elsewhere, it could be an open IF transformer or a non functioning oscillator.
Regards
Arran

RE: Trouble getting started - Eric Adams - 09-17-2012

Thanks, Arran. It is a #121. That is what both schematics are labled.
Thanks for the tips.

Codefox1, I guess you never worked on your first radio. If you can't help, don't bother me.

RE: Trouble getting started - jerryhawthorne - 09-17-2012

Eric, we all apparently have bad days. Personally I would go by the tube layout on the bottom sticker if it does have one. Please be careful as the AC/DC sets can have a "hot chassis". Meaning one side of the the AC line is on the chassis. Depending on how it is plugged in, (you can flip the plug over to plug it in), you could be looking at line voltage on the chassis. Not a nice experience if you touch and your grounded. Safety first! Most that work on these use an isolation transformer. This will keep you from grabbing the chassis and getting a real surprise. Just be careful and don't touch the chassis when the dang thing is plugged in.
Nice looking radio, lots of help here. Enjoy the hobby as when you get it running you will be hooked and looking for your next. It's worse than drugs.Icon_lol
Jerry

RE: Trouble getting started - Paul Philco322 - 09-17-2012

I have read that Philco promoted the sales of that set by offering you an autographed Bing Crosby photo! It is a neat little cabinet that was used for other model years as well. Good luck.

Paul

RE: Trouble getting started - Eric Adams - 09-17-2012

Thanks Jerry,

I do have a schematic that goes along with the tube layout on the sticker. I picked up an isolation transformer at an estate sale this weekend, so I'm set there.
I'm working on it and I'll let you know when I get it working.

Eric

RE: Trouble getting started - Arran - 09-17-2012

With regard to this being a "Hot" chassis, point in fact it is not exactly true though you still have to use caution. Philco preferred to isolate the B- or power line from the chassis by running an independent bus, then they would couple the steel of the chassis to the B-with a large paper capacitor like .22 mf and a 220,000 resistor for shielding purposes. In sets like these Philco would often use a strange choke and capacitor assembly instead of a straight capacitor in this role, I think that the idea may have been to block interference of some sort at the time, maybe from low frequency marine beacons.
I've been working on AC/DC sets for years and I never bothered using an isolation transformer, just common sense. It's actually fairly simple, keep the set unplugged except for testing, when you are testing keep one hand behind your back. It can get tricky while testing for voltages sometimes but the probes on the volt meter are insulated.
Regards
Arran

RE: Trouble getting started - jerryhawthorne - 09-30-2012

Eric, did you get it working?

Jerry

RE: Trouble getting started - Eric Adams - 09-30-2012

No, Jerry,

The caps are in and it passed the dim bulb test, but no sound. I bought a tube tester and should have it Monday. I'm sure that all the new caps are in properly, so I'll see what happens after the tubes are tested.
BTW, I just picked up a Crosley 828 console, so I should be very busy learning and doing.

Thanks,
Eric

RE: Trouble getting started - jerryhawthorne - 09-30-2012

Eric, time to check some voltages. Try the plate voltage of the output tube. Should be a couple hundred volts DC. I have not looked at the schematic to see what you have. A great test is to touch a metal object like a screw driver to the center tap of the volume control with the radio on and the volume all the way up. If you get a good loud hum, we know the amp and speaker are working and you have some high voltage. Report back!

Jerry

Here is the schematic for one version of the above radio.
http://www.nostalgiaair.org/Resources/627/M0013627.htm

RE: Trouble getting started - Eric Adams - 09-30-2012

Jerry,

I did a pin test of every tube. According to my Photofact which is for my #121, the plate voltage on the output tube was in specs. I did find a low votage at the grid and found a bad 470k ohm resistor. Since I have no stock yet, I'll pick up one tomorrow and give it a shot.
Thanks for your help. I'll let you know how it turns out.

Eric

RE: Trouble getting started - Arran - 09-30-2012

Is the 470,000 ohm resistor on the grid of the power output tube 50L6/35L6 or is it on the plate of the first audio/second detector 7C6? If the plate resistor on the 7C6 is bad then it will not get enough plate voltage to work, it's a very common failure point especailly if they went cheap and used a 1/4 watt resistor instead of a 1/2 watt.
Regards
Arran

RE: Trouble getting started - Eric Adams - 09-30-2012

Arran,

My power tube is a 50A5. I replaced the 470k resistor on the plate. The 14B6 is the 2nd detector. It also has a 470k resistor on the plate which I also replaced. I get no hum touching a screwdriver to the center term on the volume control. I do get static when I tap the 50A5. I'll be testing the tubes tomorrow and I'll give a report.

Thanks,
Eric

RE: Trouble getting started - Arran - 09-30-2012

That would be on the grid of the 50A5 and the plate of the 14B6. I said 7C6 as the first audio as most Philco AC/DCs use the first generation Loctal tubes with 6.3 volt 150 ma filaments. A 14B6 is a second generation Loctal type, I'm not sure when they came out but they use a 12.6 volt 150 ma filament, like a 12S#7 type, so I think they were a post war development. It's possible that one or more of the tube may be weak, but check the plate voltage on the 14B6, and check the plate and screen grid voltages on the 50A5, if they are low then the rectifier tube may be bad, if everything is wired correctly. If they are normal according to the schematic then either the 50A5 or the 14B6 are weak, again if you didn't make any wiring mistakes like connecting a cap or a resistor to the wrong tube pins.
Regards
Arran

RE: Trouble getting started - Eric Adams - 10-01-2012

The tubes in this set are: 7A8, 14A7, 14B6, 50A5, 35Y4. All wiring/connections have been double checked. All voltages check out except for the grid voltage(pin3) on the 50A5. It should be 55vdc and it only shows about 32vdc. Once I check the tubes I should have an answer.

Thanks again,
Eric