Need Help with AW12 Dual Dial

[Joe Miller]

Hi all,

Just pieced together an AW12 from two chassis.  All recapped and audio transformer replaced (had an open secondary).  Powered it up and was able to get a local station loud and clear, but....

I don't know how to tune this thing.  First both the dial cords are broken off.  I have the metal clips that attach to the dial wheel, but don't have a dial stringing diagram so if anyone can help or has info please let me know.  I think I will have to take the tuner assembly off to restring it.

I was able to get the local station by tuning each of the dials separately (I think one of the dials is on wrong, but not sure).  What does each dial do?  What is the procedure for tuning in a station?

Would like to hear from someone with experience with the dual dial AW12.  

Thanks,

Joe Miller

[Joe Miller]

Finally determined that the right hand dial is 180 degrees off.  Will be taking the tuner off and fixing this first.

[David C. Poland]

HI Joe,

Suggest you go to the Scott google Document site. https://docs.google.com/folder/d/0B0K3TBSz_27rNzRiZDFlM2ItN2EyMC00Y...

Then go to set folders. Open up the 2-Dial set folder. locate and open the Instruction manual.
turn to page 4 and 5 for tuning instructions.

Briefly, the 2 dials should track fairly close. The left dial is the the primary tuner for the oscillator, The right dial can be treated as an antenna tuner to peak signal strength. ( Incidentally, the previous model Scott AC-10 works much the same way,)

And yes, restringing the dial is a pain!

-Dave

[Joe Miller]

Dave,

Thanks for the info.

I got both dials restrung, powered it up and I think I now know how to tune it.  But only one local station is received.  It booms very loud, but no other stations will come in.

The plate voltages are a bit high but I think that's okay, screens are good, so not sure what is wrong just yet.  Might be the antenna coil which I will check tomorrow.  Will also try the SW coils to see if they work.

Any ideas?

[David C. Poland]

Joe,

Be sure you are using the correct grid caps for the broadcast band coils. And the other grid caps for short wave coils etc per operating instructions. Also that the contacts are clean for the plug in coils.

[Joe Miller]

Hi Dave,

1290 kHz was coming in booming and I mean loud (it's a local station here in Bloomington, Il).  I finally was able to get WLS 980 Hz to come in  okay (I live 2 hours south of Chicago, but all my other radios get WLS, WBBM, WGN, etc. very well using the same antenna),  But no other stations will come in at all.

I did an alignment check--IFs were as good as I could get them but the pad is all they way tightened down. WLS was still booming.

I cleaned the coil contacts and readjusted the dials so they are better aligned together. For some reason now the local station comes in with much reduced volume and I can't pick up WLS. It sounds like it wants to break into an oscillation but it doesn't.

My B+ is 30% high, 278 volts vs. 212 volts as designed.  I don't think that is my problem though.

I checked the tubes when I first started the restoration.  They tested okay, but not great.  Do you think I have a tube problem?  I'll swap out the 24s one by one to see it that helps.

Any other suggestions?

BTW, I think I am using the right grid caps.  I'm using the black one on the detector and not the one attached to the tuning cover.

Thanks,

Joe

[David C. Poland]

Yes, do work through the tubes, swapping them around. Hope you have a couple extras to work into your swap. Be sure to try another oscillator tube and detector. I suppose if at least one station boomed in, the audio sections are working well.

Did you carefully align the IF's? Do it twice. The 24A's are not as good as the 58's in later models, hence so many IF amp stages
The first 2 or 3 IF's seemed to be especially performance critical on mine.

Be sure you have the HI/LO switch on the amp in the high position (meaning the house voltage in high). Generally, voltage these days is are higher than in the 1930;s ... indeed, it runs about 122 Volts AC around at my house. If you are unsure about the switch position, switch it back and forth to which ever position dims the tube filaments and dial lamps. It you have a Variac, and can meter the AC voltage, try it as low as 100 volts to see your results.

Scott designed his radios to be sensitive and good at DXing.

Remember - the 2-Dial model you have (and the first version Allwave Deluxe) predates automatic volume control, so you need to adjust the sensitivity control (lower left) as per the operating instructions. Use maximum sensitivity as you seek stations, and reduce it for stronger stations for sound quality.

As go up the tuning dial (left) , you must also simultaneously turn the right dial at about the same rate to keep in "lock step". If the right dial is a little off, you will fail to get a weak station. As you tune for stations, listen for a little background hiss and static to help keep the right dial in tune with the left tuning dial. In tuning, once you have a station, do rock both dials a bit for find optimal reception.

Finally, night time reception is superior. Nighttime is when the ionosphere forms and reflects signals back to earth. Daytime reception is relatively poor. Those long winter nights make for better evening reception.

-Dave

[Joe Miller]

Dave,

I swapped the tubes for some better ones and now receive WLS (890 kc) pretty loud along with the booming local station (1290 kc) so it must have been the tubes. It doesn't have the sensitivity I hoped it would have being a Scott.  780 kc comes in faintly and it normally comes in quite loud on my other radios.  Do you think my high B+ could have anything to do with it?  Other than that everything in the set checks out.  I tried to adjust the antenna and broadcast trimmers per the instructions but it didn't help.

BTW I did find something interesting.  I bought a spare AW12 parts chassis (nice chrome) for parts so I could get this thing going.  I also bought the SW coils that came with the spare chassis.  But they don't fit.  The SW oscillator coils have a different pin configuration--they fit on the parts chassis but not on the working set.  The RF coils do fit.  Any idea what is going on with that?

Also, any other ideas that could improve the sensitivity?

Do you also have an AC10?  If so, was it hard to get it going?

Thanks for all your help.

Joe

[David C. Poland]

I think there is still something amiss, A resistor way out of tolerance maybe? bad solder joint? Did you fully recap it, including the bath tub caps riveted to the chassis? Have you checked voltages other than the B+?

There are 3 variations on the coil sets for the 2 Dial during the production run. I understand they are not interchangeable. The 2-Dial was the first of the chromed Scotts, although the tube and coil shields are polished aluminum.

Yes I have an AC-10 later version which I bought as a working set long ago. It is a very sensitive set with very good sound. Later, I bought a complete unrestored AC-10 , restored it and I subsequently sold it. The challenges were replacing the rubber wire in the amp, discovering and repairing a couple broken fine wires to the IF transformers , and rebuilding the condenser block on the amp. And replacing the leather surround on the speaker cone. It then played well first time powered up. Like the 2-Dial Scott, you have to keep the antenna control in step with the tuning dial. I have accumulated another AC-10 piece meal to restore sometime.

The AC-10 receiver is built on a bakelite panel. Copper box encloses the IF transformers and the interstage audio transformer. The panel sags over time, but was supposed to be floated on a foam pad to support it and provide a degree of microphonic protection from cabinet vibrations. The first version uses a large brass escutcheon, Later versions have the more common small dial escutcheon. There are 3 amp variations, all built on a steel chassis. The first version uses 2 type 80 rectifiers - I have never seen one. The most common has an 80 and the pair of 45's in push-pull, Some amps have an Amperite line voltage tube that deals with AC line variations to provide a steady 80 volts or so the the power transformer primary, instead of the high/low switch like your 2-dial amp. Many of the amps were wired with rubber insulated wire that has dried out and must be replaced for safety. The speaker is a 10 inch Rola pedestal speaker with output transformer and has a Scott tag.

[Joe Miller]

Yes, fully recapped and all resistors replaced. I rechecked them and they are all in spec value wise.

With the B+ 30% high, all the plate voltages are high as well, but I don't think that should cause a problem.

I think I'll remove all the coil shields and replace with the nicer ones from my parts chassis.  I've verified the coils are good from the grid caps to ground so I shouldn't find a disconnected grid wire like I did on my AW23.  But what the heck, that's the only place I haven't looked yet.

I'll also check all the solder joints.

Joe

[David C. Poland]

Try reducing the line voltage. Variac, or a light bulb tester with a 200 or 300 watt light bulb in series with the radio or a really hefty power resistor. Or a power resistor ahead of the the choke to knock 30 or so volts off the B+.

Norman or Kent - any other thoughts?

[Angelo]

One thing to remember once you have replaced parts let them burn in  IE play the set at least 8 hours befor alignment.Do the IFS 2 times .Set your varac at 110 volts ac let the set warm up at least 1 hour befor alignment this includes test equipment to!Now on the sheilds  on some sets they can change how sensitive the set is.(Philly 30  exsample)! Make sure that you adjust ant as you tune the bands..My allwave deluxe 12 with avc get good reception but i use a big ant 100 foot long try longer ant and change its direction.Make sure ant tuner is hooked up right ..Angelo

[David C. Poland]

Joe,

A long wire antenna, but not too long as per instruction manual - at 40 to 70 feet including lead in wire, for the broadcast band. A ground may be important for your location, Long wire antenna recommended oriented aprox east-west. Antenna end(s) insulated. Signal loss from passing to close to other objects, especially metal like eves and downspouts? The tubes of the era didn't have the gain of later 1930 tubes designs, so gathering signal is more important.

Another thought ... some grid caps have braided shielding. Check that the braid is grounded, but that the insulation under the braided shielding is not compromised and shorting/leaking to ground. Trace the grid cap to the other end of the IF coil to assure the grid cap wire has not broken off inside the coil can robbing you of amplification. With a signal generator, can you verify each IF stage is effective by noting loss of volume as you slightly detune each stage, especially the first 3 stages? Be sure your 2nd detector 27 tube is very good. Have the lower sensitivity switch to max - full clockwise, - then reduce for a strong station to keep from overloading the 1st detector.

Getting back to voltages running high now days, note that the volume control is not in the audio section. Rather, it controls screen grid voltage of the RF and IF amps tubes. Have you tried alignment at somewhat reduced AC and then operated the radio?

On the IF cathode resistors, values vary from tube to tube - each about correct value? and the associated caps?

With the Broadcast coils, the 2 coil shields should be mounted, but on Short wave, the 2 coil covers should be removed.

Angelo, .... my AW 12 Deluxe w/ AVC is a great performer, too - & has the Jensen Pedestal speaker. Very sensitive.