[morzh]

Questions:

1. Is there such thing as the voltage diagram for 39-690?
2. The reason(s): a)well, it's just nice in general to have it, it is a very helpful piece of documentation, and b) well, right now is exactly the case where I could use it.

I decided to listen to the tweeters, and while at it, I measured the voltages across their field coils. On one of them the voltage is 80-plus Volts, on the other - 44 Volts. While the input voltages before the coils are close, the outputs are different.
The coil that goes to the tuner chassis and connects to the R69, a 500 Ohm resistance, is the one whose output is lower and the dropout across the coil over 80V. This will result in over 11W dissipation (vs under 4W for the other tweeter coil). Dunno if it is normal or not.

Otherwise, the radio sounds nice, considering the patched main speaker, open volume suppressor long wire, and a somewhat scratchy volume control (I'm reluctant to open the dual ganged potentiometer) and the speakers being on the table right now.

[morzh]

Well....I thought, if no one knows the voltages, and all that worries me is currents, I might chart the currents myself.

So. The lower tweeter (in the sch) field coil feeds:

1. The field of the main speaker. It is 262V over 4360 ohm, or 60mA. The heaviest load on the line.
2. The main chassis. Easily measured by the dropout across R69, which results in 20mA.
3. The 6F6 plate current. Measured by yanking the tube. The result is about 33mA which isin line with its datasheet.
Total current is about 120mA (75V over 620 ohm) which is close to the sum of the parts.

So it seems normal that the voltage across this particular field coil is 75-80V. I should stop worrying.

[morzh]

And, speaking of the tweeter speakers being counter-phase and the series capacitor being too low: my though of why no one noticed that initially is: the main speaker, used by Philco, is the same exact speaker that 37-116 and 38-116 use, with the exception of the field coil resistance (which in these is low, as they are used as filter, and in 38-690 is high as it is used as a load and not as a filter) - the PN for the cone and voice is the same. So, the speaker being a full midrange sufficient for producing Hi-Fi sound, the absence of the tweeters' action was well masked by the main speaker's performance.

[morzh]

Forgot to add: I decided to see if my tweeters were connected counter-phase as expected. When disconnecting them, I labeled the wires, so when reassembling them on the workbench I used the original wires sequence.
The speakers wired left-to-right as 3-4, 3-4.
Now if they were counter-phase, the wires that connect them in series (that are essentially 1 wire and are ohmed out as near-zero ohm) would go to the same pins on both speakers; but they went to the different pins.
So if you imagine one over the other, the pins would be wired as "Z" letter, that is the GND going, say, on pin 4 of the first speaker, then the wires connecting the speakers in series go to pins 3 of the first one and to the pin 4 of the other, and then the transformer wire (top one on the sch) goes to the pin 3 of the other speaker.
So everything was OK; whether because of someone corrected that in the past (yes as I said before, the radio was repaired some time in 1950s I guess) or it was wired right from the beginning.

PS. My capacitor initially was 1.5uF and as I said, the tweeters were not that noticeable. I parallelled another 2.2uF cap, making the total capacitance 3.7uF (vs 1uF original) - now they are quite noticeable.

[morzh]

Yesterday and today was putting back the dial assembly.
I decided to take it apart.
There were problems.
Probably due to the dial hub having damage and the band illumination screen being badly damaged, someone took it apart but made some mistake when putting it back together.
When I defeated the vernier, I had some trouble realizing the lock pin action, but eventually got it working.
So, a year ago I bought a 37-116 with extra chassis. This proved helpful as the band illumination screen was intact on this one, plus the volume off contact cardboard gasket was also in need of replacement.

I suspect there are other problems with the radio, but first will attemp to align; I suspect an open transformer in one of the RF staged: several things point to that even though it receives well on BC without any antenna.

[morzh]

Probably bad switch contacts too.
I did Deoxit it before, so I repeated the blast, soaking all wafers and working it.
I don't remember if I used Green before, now it is Red.

[morzh]

Still some ails that plague it. One is this switch, the BC band secondary solders to the switch contact that is unreliable. No good way to reach it.

Then there's an open coil primary at the 2nd band, which I think I'll leave be as it is the police etc band, not much there anyway. Other bands I aligned.

Then the dial...am not sure as to it being exact same with internal ring, as in 37-116 deluxe, as then it means the inner ring is missing and someone riveted a piece of aluminum to the opposite of the stub that used to hold the ring and now he two are used to hold the dial which otherwise is good, but it slips and not held reliably.

Then there was this hum. Pretty pronounced. Right across the bass field coil I saw a pretty large ripple. I tried caps tono result. Then I started tacing it and traced to the power amp 6F6 input. That traced to the tuner output, the second audio 6N7, metal case. I realized the capacitor that is the output of it was hidden and I didn't restuff it. Fixed it, again to no result. So I cannibalized my 37-116 chassis with a glass 6N7G and....the hum went down a lot.
Then I looked at the second 37-116 chassis and it had a metal 6N7, same as I have, and after the change the hum was practically gone.
That was the tube!!!! The ripp!e on the scope also went way down.
The tube did test well - I tested all of them.

Well, at least some good news for today.

[morzh]

Soldered the volume squelch wire to the ato tuning dial's contact.
The volume intermittently started disappearing when rotating the lever without being pressed.
After two hours or so of trying to align the contact, trying the gaskets etc from the donor chassis, I realized that the insulation film, around which the moving contact rotates, is missing.
I took the vernier crom the donor chassis, now it is working.

I thought of trying a layer of Kapton film but not sure how durable it would be.

Meantime, i have become an expert in the auto dial assembly and now can take it apart with my eyes closed and without any notes. Having said that, I wasn't able to extract the retaining pin from the new vernier. But then itmoves just fine.

[morzh]

I was afraid the magnetic tuning was hosed due to some coils being bad, tried the scope only to see no output whatsoever from the discriminator etc.
Then it occured to me to try to align the circuit, to which the procedure is there in the docs.
I aligned by ear, though obviously aligning by meter would be better; I also read sonewhere in Rider's they swapoed 85A and B trimmers, but decided to folow the instructions as mine are from Chuck and don't look like Rider's.

Anyway, tuning started to work, pulling in the signal when de-tuned, first from generator and then the local station. I might repeat the alignment, now with the meter.
If all works, I will assemble the radio and put to work.

[Ron Ramirez]

Come on, Mike, You know better than to align by ear, especially a 38-690. Use the proper tools and do it right! The Mighty 690 deserves no less.



P.S. The Magnetic Tuning will not work correctly unless it is properly aligned. And it is not an easy job. Been there, done that...

[morzh]

I (turning my nose up) happen to have a very good ear.

There will be things in this radio I will probably won't be fixing all the way, including that police band antenna coil. This will require too much an effort for to little gain.
I wish I could improve the band switch performance too, the BC band antenna coil secondary contact is iffy. I probably spent half a can of Red DeOxit. All the bands are fine except this one. It has improved but not 100% reliable. And taking the switch out is out of the question.
It is where the grid of 6U7G RF Amp connects to B9 pin of the switch and then the switch makes to the B8. The B8 is the one that does not reliably make. And it is inaccessible. I was able to direct the straw of the sprayer directly to that hole in the wafer at B8 where I can see contact and spray some Deoxit right there. After that it sometimes work but sometimes it goes to 20-30-100 Ohm resistance.

Not sure what to do, maybe you know some tricks......

[Ron Ramirez]

Other than using a little full strength D100 from a tube or bottle and a toothbrush, which would necessitate pulling the RF unit apart to reach the contact in question; no. No, I don't.

[morzh]

That's what I thought.
And it is not enough just to pull the RF, which would be less than half the trouble: it is the way the switch is packed in there. It will have to be taken out of the RF unit afterwards.

[morzh]

OK, guys,

Need help with assembly.

This is what I have with the tuner:

   

This is what's left unused:

   


The tuner chassis should probably be held in proper position where it is aligned with the front by something other than the shipping wooden blocks.
As I said before, the radio was partly taken apart before I came so I do not remember all the fasteners, and in the inclined models of 1938 it is different from the ones from 1937 where it is parallel to the floor and is held with one 4-40 screw.

[tbone]

The grommets need to go on two small shafts on the front of the sub chassis before it's installed in the main chassis. Then you slide the front of the sub into the two openings in the mounting bracket and slide back. So these brackets have elongated rails for the grommets.

I'll try to get pictures from mine later today.