Setchell Carlson...588 dial, 407 cab, 420 chassis(?) Serious need of a schematic.

[marloubow]

Reese,
Thanks for hanging in a bit further. Will go over your suggestions and post.
Thanks
Martin

[marloubow]

Reese,
It was as you said and I checked it against closer-up, original photos.
I removed the 1000ohm resistor and put the right hand choke wire back on pin 8 of 25Z6.

Voltages are up....
25L6 A) 106.4 B) 105.2
6Q7 pin3, 105.8 pin6, 107.2
6K7 Front, 107.0 Back, 106.9
6A8 105.7

There is a loud hum @ 6Q7 when touched with the cap wire removed.

Martin

[Reece]

Good! Power supply and audio section are working.

Hoping against hope, put an operating radio, can be a transistor radio or any kind, tuned to a weak station around 1400-1500 right next to your S-C, turn on the S-C and tune it all up and down the dial. If your oscillator is working should hear a squeal or rushing at some point in the other radio.

Does your 6A8 test strong?

[marloubow]

Reece,
The 6A8 test "good", how strong that is I do not know. The only tube tester I have is an emissions tester.

I tried the 2nd radio trick and couldn't get the functioning radio to whistle, squeal or break the signal no matter how hard I tried. I tried with a small transistor radio and with a receiver at various points on the dial...no wanna' squeal!

What do you think?

thanks for the help
martin

[Reece]

Shows the oscillator isn't working. The tube should be OK per your tester. Carefully check the wiring against the schematic of a typical 6A8 oscillator/mixer in the article referenced. Also check continuity of each winding on each of the three exposed coils, just to see that no wires are broken. I have a hunch they aren't, since the radio worked weakly in the beginning. I'm thinking there's a wiring error.

Here's where signal injection would come in handy, working back from the first audio tube.

[marloubow]

Reece,
I have continuity thru all my coil connections. The only place I didn't get a continuity signal was thru the donut ring around the coil, but I did get resistance.
I couldn't find any misplaced wires.
Thanks for the suggestions.
I'm going to ponder my next step. The tech I use is a wiz, but he doesn't work for free. He's good and it's right that he gets paid.
As much time as you and I have put into this, I really don't want to shelve it.
thanks again
martin

[Reece]

There must be "one of us" nearby with test equipment who could help you out.

[marloubow]

Hi all,
Time to man up...
I found the problem and I'm not exactly excited to share the news.
Wrong value resistor, 47 ohm instead of 47K spanning pins 1 & 5 on the 6A8...rookie mistake. Should have looked for wrong values first.
My apologizes to all who helped, especially reece.
At least now I can proceed to the rest of the restore. Stain & poly or Tung oil on the cabinet, replace the grill cloth and new dial glass.
Will post photos of finished piece.
Thanks again.
martin

[Reece]

Congratulations! It's happened to all of us. Glad you found it!

[marloubow]

Reece PM me this...

"You say it's working: how well, what does it need now? With 10 or 20 feet of antenna it should pick up locals during the day and plenty of distance ones during the night as it has 2 IF stages and was a farm set, made for out in the boonies. Do you get OK volume? Do the stations come in where they should on the dial?

Try an alignment tweak: I think the rear condenser gang on this set is the oscillator. If the stations aren't where they should to be on the dial, tune one in near 1400 that you know the frequency of. With a small screwdriver carefully adjust the rear trimmer on top of the condenser a tiny bit either way. The station will move and you can turn the dial to follow it up or down wherever it needs to go.

Once the stations at the top of the dial are where they ought to be, tune in a weak station somewhere from 1400 to 1600 and carefully adjust the front trimmer on the condenser for maximum volume.
There's a trimmer in the middle of the underside of the chassis next to a coil, and I think that's the padder for the low end of the dial: if a station around 550 to 650 isn't where it should be, I think that trimmer will move it. The oscillator trimmer and the padder will somewhat interact so you may need to go back and forth a few times.
Next tune in a very weak station near the top end of the dial. Use a non-metallic screwdriver or take a small screwdriver and wrap tape around the bottom, just barely leave the tip exposed. Topside of the set: adjust the trimmer on top of the round can for max volume. It shouldn't take more than 1/8 or 1/4 turn either way to max it. Then do the same with the 2 trimmers in the top of the other two square cans.

If you didn't do it yet, squirt cleaner on the tube pins and plug in and out of sockets while wet.

What about the speaker? Wasn't it dragging on the pole piece? There are ways to fix that depending on what's happening."

I haven't run 20 ft of antenna wire yet. I'll tackle that tomorrow. I have the unit in my basement at the moment with 10ft wire attached to a copper wire wrapped >< (crisscrossed) antenna. I was able to adjust AM 1390 sports to it's proper place on the dial, as well as 960 news talk station. There are quite a few stations that are weak that I should be able to pick with higher antenna placement.

Volume is adequate.

All the sockets have been "deoxit-ized".

The speaker seems to be fine. It has that "classic" AM sound.
The mechanical sound that it had before is gone.

The dial light is not functioning. The bulb filament looks intact.
Before I try a bulb swap, what kind of voltages should I be seeing at its base?
At the moment it's...-.013mV DC. The supply wire terminates at the (utah) 50 ohm wire wound resistor.





Thanks
Martin

[Electronic M]

6.3V is the most common dial light voltage. If the bulb has resistance that is not infinity follow the wire back checking voltage between it and ground(if that is what the outside of the socket is connected to) for something more than a volt. And if you find fillament voltage then there is an open circuit somewhere between there and the bulb.

Correct me if I said anything wrong. All dial light failure I've deal with were burnt out bulbs.

[marloubow]

Tom,
Thanks for pointing out the obvious...I have no resistance...dead bulb.
I retested my voltages. I'm still at, -.013mV DC, but find I have 8.10V AC.
I don't recall (limited) that I've come across a bulb in an audio piece that was AC powered.
Is this one of the "perks" of being a "hot chassis"?
Does a bulb care if it's AC or DC?

Thanks
martin

[marloubow]

guys,

Well one thing leads to another. Found the answers to my bulb "problem".

As mentioned before, there is a delay in my on/off switch. For some reason it takes somewhere from 5 to 10 seconds after switching on, for power to start flowing thru the circuits. I'm not talking about tube warming.
This is why I thought that I had a problem with my bulb socket/circuit.
I would turn on the power and no light. However if I wait 5 to 10 seconds, I hear this sizzle/crackle in my switch pot, the dial light glows brightly, then dims and I start to see the tubes begin to glow as well.
Now the problem is quite possibly of my own making. Back when I was waiting on components, I decided to flush the pot with deoxit because it had a slow gummy feel to it's movement.
I have a feeling that what I flushed was some dialectic grease of sorts necessary for good connection.

Does this sound right to you guys? I'm all ears.

Martin
Here's the pot before and after.

[stusnyder]

I don't think it matters if it's ac or dc...as long as you don't exceed the rated voltage.

[Reece]

Hook your AC voltmeter across the dial light with the set off. When it first comes on, at what does the voltage first peak? Then it settles down to 8.1VAC with the bulb lit, right? If the peak isn't too much, you'll just need a simple resistor in the bulb line to drop the voltage to 6.3V or a tad under. About 15 ohms at 1 watt.

Your switch contacts are dirty or have lost their springiness and aren't making good contact or have a balky snap mechanism. It's possible to drill out the rivets and take it apart and fix it, but it's a lot easier to just replace it. Unsolder the wire from the high end of the pot (terminal farthest from the chassis ground terminal.) Measure the resistance between the two end pot terminals. It's probably 500K or 1 megohm. You'll need a pot with audio taper and SPST switch attached. The length and type of shaft (round, half round, etc.) have to be noted. One place to get them is from Mark Oppat. He can fix an old control or provide a new one.

Edit: actually, looking at the picture, if that pot were taken out of the chassis, you'd bend the tabs up on the front of the pot and separate the pot from the switch. Then looking inside the metal shell you'd see how to get to the guts of the switch.

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