[BrendaAnnD]

I'm working on a 16B, and have some service info, waiting on other, but there seem to be some production changes (and I have no idea of the code number) that are somewhat confusing.

The main one is in the LO circuit. The schematic and parts layout pages show a 10K resistor from the bottom of the oscillator coil to ground with a capacitor across it. However, there is no such resistor in the radio.

Also in the LO circuit, someone has placed a 37 tube where a 76 is called for. The 76 has a much higher mu than the 37. The alignment is problamatic, plus there is no oscillation on the entire bottom half to 2/3 of the two top bands. I'm ordering a 76 to put in there, hopefully that will help some.

Another problem is the shadow meter. There is a barely perceivable movement with a VERY high level signal, otherwise, it sits in one place, with the lighted portion being about the left 3/8 or so of the target.

If anyone has any suggestions for things I can look for or change out, I would appreciate them.

[Ron Ramirez]

Brenda

Sorry no one has answered before now.

I was looking at the schematic this morning before work. I see two 10K resistors in the oscillator circuit. Can you specify which one you are speaking of, please?

As for the shadow meter. I am hearing more and more about the magnets in these losing their magnetism. I have a few which have this problem, also - good continuity yet little or no movement. Having not tackled this as of yet I will defer to others as to how to re-magnetize that small magnet - I look forward to learning more about this issue, myself.

[BrendaAnnD]

When I look at the parts placement sheet, I don't find either of them in the radio. The obvious one connects to the ground at the HF trimmer just next to the second wafer from the front of the bandswitch, and to that section of the bandswitch.

I guess I'll have to pull the shadow meter apart and see what is up with that... not something I was looking forward to.

For the record, this is a darn nice performer, even with the issues it still has.

Work performed so far:

Replace 2x 8uf filters with 2x 10uf/500V
Repack filter can
Repack bakelite caps
Replace resistors as needed (up to a point, still working my way through).
Apply DeOxit to all ground connections on the tuner rotors (still trying to figure this one out... but the rear end of the rotor shaft had no ground contact, while the front did. One would think that if it connected in one place, it would show some continuity all the way..)

[Ron Ramirez]

The two 10K resistors I see in the oscillator circuit are (18 ) and (20A). (20A) is in parallel with an .003 uF mica cap.

Here is an under-chassis view of the 16:

[Image: http://i326.photobucket.com/albums/k420/...70c84f.jpg]

[Chuck Schwark]

Brenda,

You will get all pertinent Model 16 Philco Production Change Notes with the info packet you ordered.

Could you please list the tube complement of your set, so I can narrow down the probable Code version of your set?

The Model 16 went through at least eight Code version revisions and many, many Run numbers (minor component changes) within those major Code versions. Want to sent the most accurate info I can for you. Riders usually never can give you the correct info, as they did not always re-publish subsequent changes or revisions from the manufacturers, as I have found out for Philco lit from that source.

Thanks,

Chuck :-)

[TA Forbes]

The 37 and 76 can be substituted for each other. Personally, I prefer the correct tube in place, but fyi...

I don't think that the osc issue has to do with the tube, but agree putting the correct tube there is the way to go. I would recommend you continue to replace the rest of the wax/paper caps if not done so already.

Have you made sure that you are aligning on appropriate peak and not a harmonic?

Have you tried adjusting the distance of the shadowmeter bulb filament from the aperture of the meter? This controls the width of the shadow.

Moving the bulb filament from left to right controls centering.

Be careful not to short the hot end of the bulb socket to the mount, it is, as you shall see, easy to do.

[BrendaAnnD]

Ron,

The one on the schematic and parts layout that I cannot find is 18.

Chuck,

The tube compliment is as follows:

Rect. 80 (schem. I have shows 5-Z-3, but I think even the socket shows 80 on this set)
Outputs. 2 x 42
Driver. 42
Osc. 76
1st Det./Mixer 77
1st IF and 2nd IF. 78
2nd Det. 37
1st AF. 77
QAVC. 78

[TA Forbes]

The 5Z3 rectifier was only used on console models that used the U2 speaker.

[Ron Ramirez]

Brenda

Does your set match the under-chassis illustration I posted above? 5-band model with vertical mounting power transformer and large metal multi-condenser can next to it?

Just wanted to confirm we're talking about the same set here...

[BrendaAnnD]

[attachment=1402][attachment=1401]Here are pics of the top and bottom of the set. Hopefully these will help identify its particular run.

[Ron Ramirez]

Oh yeah, that's perfect, thanks. No doubt about it - this is a Model 16 Code 121.

And you're right - (18 ) appears to be missing. Factory goof? Removed by a previous "repair person"?

[BrendaAnnD]

Ron,

I haven't had time to try to track it down as yet, but did measure resistance from that point to ground, and found 10K in the first two or three positions of the bandswitch, 5K on the others. Seems that resistor is in there SOMEWHERE... but the question is where.

[BrendaAnnD]

Here's an interesting issue:

In checking the LO, I found that even on the lower bands, the output waveform is not good. It's the ugliest cathode follower I've ever seen.

Looking at the actual oscillations at the plate, waveform shape is a nearly perfect sine. However, looking at the cathode follower, it's more like a half wave rectified signal. All but the top 10% or so of the lower half of the waveform is not there. But it's not a clean clip, it's more like a slight upward slant at the bottom of the waveform.

I can't find or figure any reason for this, other than a bad tube. It speaks to inadequate bias, but the voltages are very close to spec. I've replaced the 500 ohm wirewound in the cathode circuit with a 500 ohm flameproof, but no difference. Checking other components in the circuit I found no problems.

All of this, added to the drop off on the lower end of the high bands, I can only think of the tube, but perhaps there's something in what seems to be a very simple circuit that I'm missing.

[TA Forbes]

Possible that C17 .00125mFd is bad?

R16 5K ohm same same?

[BrendaAnnD]

Well.. there's good news and not so good news.

The good news is that I've managed to repair the shadow meter, as well as the tuning mechanism. The shadow meter problem was twofold: the vane inside was bent so that the beam couldn't display properly. And, the second was organic in nature... there was an industrious spider's egg sac in behind the vane, keeping it from moving. I removed that, and it instantly began complying. So, that's great.

Now, the not so good news.. not only can I still not get the two top bands to work on the low end, I've also lost linearity on the broadcast band. I attribute this to a possible faux pas on my part. Having tried everything else (new tube, replaced resistors and caps in and around the LO), and knowing that some Philco sets have been known to have coil problems, I removed the LO coil and gently heated it to melt the wax coating, and brushed it off, thus hoping to clear any moisture that might have been trapped within.

Upon reassembly, the upper bands had really not changed, but now I can't get anything like tracking on band 1. If I align it per the manual, the low end is sort of close, but by the time I get to the middle, 1242 appears around 1340 and 1440 is off the band. Retuning to get 1440 where it should be, 603 is now near 550, 973 is at 890 and 1242 is at 1090 or so.

Soo... I fear that I have damaged the coil, and it may have been possibly damaged before, and I made it worse.

Suggestions???