[tbone]

Not much Philco time this week I was able to get the auto tuning working good and both switches doing their thing. I also found a bad ground rivet on the amp chassis, an intermittent around the RF amp that makes that stage die, and oscillation on bands 3&4 when no antenna is hooked up. So lots to do and not much time in the next week.

[tbone]

I fixed the bad ground rivet connection on the Amp chassis, and now the hum is gone. Troubleshooting the intermittents in the RF chassis is next. Should have some time this afternoon to start. I will pick a few monitoring points for voltage around the 6U7 so I can watch what happens when it goes out. Suspect the bandswitch or a bad solder connection (radio was full of them from previous repair person).

I have the pictures of the painted chassis's in the link below which shows how they look completed. Just click on the photostream for a full compliment.

https://www.flickr.com/photos/152428891@...ed-public/

[tbone]

I managed to fix the dial mechanism and stopped the rubbing between the dial and mask. I also lined up the dial properly and everything tracks good now.

I re-wired the tweeters per the fix listed here on the forum. Not only were the tweeters out of phase, but the OP transformer leads were reversed. Changing those made a big difference in the sound. Can't wait to get it in the cabinet to hear the true sound.

I am still working on the intermittent in the sub chassis. Seems to only happen as the set warms up within the first 5 min. The sensitivity drops off and then comes back. Normally a .75-1uV signal can be heard with the service monitor hooked directly, so I no the radio is up to snuff. I have swapped tubes around, but I need to dig out other ones from my stash. Work in progress, as I want this right before I call it done.

More to come.

[tbone]

Today I spent some time on the radio. My question is, do the shortwave bands 2-4 align so the point of best sensitivity is the point where the carrier is on the correct dial position, or are they off somewhat? My radio, especially bands 3-5 have the best sensitivity when the alignment frequency, (7.0, 11.0, 18.0) are below the correct dial marking by quite a bit. I checked the images and they are below the alignment frequency by the IF frequency, so I know I'm right.

Should I be using some kind of dummy antenna? I don't see it listed in the instructions?

Just curious what anyone has run into with this radio.

[morzh]

My shortwave bands frequencies are fairly close to where they should be.
This said, the trimmers and padders allow quite a bit of adjustment.
I did not try absolute accuracy but it is pretty close.

[tbone]

I can get them to line up pretty close, but then the sensitivity drops off. Which tells me something is not right. Broadcast band is dead on one end to the other.

[morzh]

You do align all compnsators in order suggested (like for babd 5 at 18mC) ?
And you have the Mag Tuning off?

And....you trust your sig gen and verified all bands with a counter?

[tbone]

Yes you are correct about the order which I did follow. Mag tuning is off. My sig generator is a IFR 1200s and from what I've seen, it's dead on. I can zero beat with known received signal.

Seems to be that the RF stage is not tracking on these bands.

[Radioroslyn]

Might try connecting your signal generator to the cap on the mixer (bypassing the rf amp) to see if the sensitively is reasonably flat across the band.

[tbone]

I found one thing of interest that might be the problem. The tuning cap is not all the way closed when the dial is at the low end stop. Just to clarify, when dial is at the mechanical stop and gang is closed, which set of lines should the tuning light line up with? The last set of lines on the dial, or the single line just past the low end on the BC band?

This may be my issue.

[morzh]

Did you see if your dial's notch is over the ridge on the hub over which it goes? Does the dial have any play?
I think it is those single lines that separate the text from the scale that are supposed to line up with the light line.

And that stop cannot really be adjusted.

[tbone]

Dial is corrected, but no difference. I looked through the osc section and did find this interesting. C41&42 are not present. I can't find any place where they were before either. C43 is not a 1300pf mica but a adjustable padder instead. Definitely factory installed as there is a mounting hole and a second hole for the tab so it won't move around.

Obviously there are no instructions for this padder, but it will effect all shortwave bands.

Any thoughts on this finding?

[morzh]

I'm not sure C43 would affect it this way. I am also not sure it can be a padder. Are you sure you are positive this is C43? This in the sch is an AC common for the Oscillator coils that are switch according to the band chosen, and the actual frequency affecting padders are C39, C40 - they are at the other end of each coil.

[tbone]

According to the Schematic it is C43 and is in series with the common on the osc coils. I am going to look through other schematics and see if I can find something similar.

[tbone]

Morzh,

Thank you for pointing me in the right direction. I redid the whole alignment process from start to finish and this corrected the alignment making it acceptable on all bands. I also verified and corrected the two IF peaks while in wide band operation.

I used a procedure for the 38-116 which had the same osc section for run 125 as the 690. There was more info about how to align the 18 MHz band and rocking all trimmers. Also, the correct dial alignment procedure was with this schematic.

Sensitivity is good. It takes a .75uv signal to break over the noise, and at 1uv the tone is guide audible.

I also found the two mica caps, which were right in front of me

The 1300pf cap is indeed a mica padder. I left it alone. For those of us that have worked on some late 30's and early 40's Zeniths, you'll be familiar with the dual fixed padders they have. Pretty funny that it's a fixed padder

I'm calling this one done. I just have to move around some preset screws to take the place of the broken ones. Cabinet is next.

Thanks to everyone for their input.