Good news and bad news today. I finished checking all the wiring and found and corrected one mistake. So I decided it was time for a test. First I put in all the tubes except the rectifier and gradually cranked up the variac. No sparks, no fire, no problems. So I put the rectifier in and again slowly cranked up the variac. Everything looked good. It drew more current than I expected...about 0.75A. So I don't know if that's bad or not. Also, the panel lamps don't light. They are driven by the filament circuit and since the tubes are lighting up I would expect the bulbs to light up as well. They measure ok, so I don't know what's up there.
EDIT: I think I just figured out the panel lamps. It dawned on me that there is just a single wire to each lamp, so the housing will need to be grounded.
The bad news is that I am getting no audio at all, except a little bit of hum with the volume control turned up past half way. I did not re-install the pushbutton assembly yet because I wanted to make sure I was pretty much done working on the bottom side of the chassis to avoid possible damage to the pushbutton assembly. But now, looking at the schematic, it looks like I need to install them. It looks to me like the phono pushbutton does some pretty important stuff in the circuit. So I'll try installing them later tonight or tomorrow and see what happens.
Also, I have a suggestion for an improvement to the Phorum...where is the proper place to post that?
Rich
(This post was last modified: 04-18-2017, 05:23 PM by criageek.
Edit Reason: Figured out the panel lamps
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Drat! Wired up the pushbutton assembly and still no audio. I've done some testing and the audio section is ok. But I can't get a modulated 455kHz signal through the AM section. Then again, I'm not certain I'm actually injecting a modulated signal. I have a B&K E200D that's just been sitting for 30+ years. I did open it up and clean all the switches and controls, and I know the carrier is there, but don't know if it's the right frequency and don't know if I'm successfully modulating it. I guess I need to test my test equipment before I test the radio!
A side question. Is there a good (safe) way to clean the speaker cone? This bad boy is in GREAT shape, but is quite dirty.
Others may have different / better ways of cleaning dust bunnies from speaker cones (and I'd love to hear them too). Here's my method: I use one of those aerosol cans of compressed air and GENTLY blow out the dust and dirt. Key word is GENTLY...don't pull the trigger all the way for a full power blast or you're likely to blast your way right through the paper cone! To me it's safer than trying to use a small brush (which is another option) where one wrong move or too much pressure on the brush and you're through the cone.
Thanks Greg - I figured I'd give it some air from the air compressor, but don't have high hopes. I've tried that with the rest of the radio and it really doesn't touch it. This stuff is from sitting in a humid basement for many years. I won't touch it with any kind of liquid unless someone can tell me what works without damaging it, but I don't think this stuff is going to come off without some sort of liquid. I don't know...maybe a soft brush of some sort? I don't think it's near as bad on the outward surface as the back, since it was protected by the grill cloth, but it still has some grunge on it.
Rich
EDIT: Oops...I missed where you said you wouldn't use a brush. But this thing seems REAL sturdy and thick. I probably won't do anything to it unless someone can give me a really sound suggestion. The gunk won't affect the sound...it just looks bad.
(This post was last modified: 04-20-2017, 07:03 PM by criageek.)
(04-20-2017, 08:50 AM)jcassity Wrote: ...hopefully its a simple ground termination missing.
Thanks jcassity! I'm pretty sure I'll get it figured out. I've become pretty stubborn in my old age! I haven't forgotten about your antenna coil situation...just haven't looked at it closer yet. Here is a closeup picture of the one I have that looks the most like your's.
ok,, i think with your pic on the antenna, i see a pattern, yours is cleaner than mine.
i think of this as a Two Tier wire winding ... so ...
top tier one wire terminates at the 3 o'clock , your right hand side per pic
bottom tier one wire terminates at the 6 o'clock, center facing us in the pic
top tier final wire termiates at the 9 o'clock (assumption, cant see), your left side per the pic
bottom tier final wire terminates at the 12 o'clock (assumption,, cant see) center facing away from us in the pic
the bottom tier terminate at the 12 and 6 o'clock.
criageek Wrote:Also, I have a suggestion for an improvement to the Phorum...where is the proper place to post that?
Rich, we welcome suggestions - just contact a member of the mod/admin team. Please check your private messages - a moderator has already sent you a private message on that subject.
I've done a little bit of testing to see why I'm not getting any audio. I bugged the connections for the phon pushbutton and that all looks good. I'm wondering if I have a bad 7X7 or 7R7 tube. I get no popping when I change the bandswitch...seems like I should at least get that. Other than checking continuity on the filament pins I have no way of testing the tubes. Any suggestions? It looks like I can get the 7X7 and 7R7 from Tube World for about $10 plus shipping. Seems reasonable to me. I can get all the tubes for the radio except the 5Y3GT (already got one of them) and the 6V6GT output tubes (I think they are good) for about $41.
I'm both encouraged and a bit stumped now. I figured out that my signal generator was not producing a modulated signal and fixed that. There is a trimpot inside that needed a little adjustment in order for the internal oscillator to start. Once I found that I adjusted it for the best looking sine wave and now I get a nice modulated signal. So I went through the AM tests in the documentation Chuck sent me and all succeeded. Including injecting a 1000kHz modulated signal into the antenna terminal and tuning to it for a nice tone through the speaker. I would think that means everything is working correctly, but I still get no stations. I even dug out the loop antenna from the cabinet and attached that, but still nothing. Any suggestions for how to proceed?
I'm still in need of some guidance on this. Here is some more info in case someone can help me out. This all pertains to the AM band, but I get nothing on short wave or FM either.
The AM oscillator is running. Here is a scope image (10v/div):
When I tune up and down the dial, there is nothing except some slight hum when the volume is most of the way up, except one spot very low on the band. At that spot I get some static that sounds very much like I'd expect to hear from a radio that is not receiving a station. Here are two scope images. The first was taken when tuned to the static spot (1v/div), the other was taken when tuned to the middle of the dial (0.1v/div).
And here is where I took those images.
Can someone give me some guidance and point me in the right direction?
Have you checked the frequency of the oscillator? You can figure it it out by the settings of your scope time base (uSec/ div), or by placing a portable radio close by and tuning it 455 kHz above the Philco dial setting.
If you set the Philco to 1000 kHz, you should hear the osc signal at 1455 kHz on the portable.
There was one more thing I forgot in my previous post. In the troubleshooting tests in the info Chuck sent me there is an oscillator test. In it, they say to connect a voltmeter between pins 1 and 4 of the 7F8 (refer to the schematic posted above) with the positive lead on pin 4. It says you should read about -3v. When I do that I get +4v. When I measure from pin 4 to the chassis, I get 0v. When I measure from pin 1 to the chassis, I get -4v.
What do my results mean? The attached instructions are for the FM tests, but the AM oscillator test is identical.
Thanks,
Rich
(This post was last modified: 04-24-2017, 05:35 PM by criageek.
Edit Reason: Add informational text
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