EH Scott Radio Enthusiasts

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AW-12 Deluxe AVC-- IF alignment and part question

After quite a while I'm getting back to the AW-12 and I'm hoping I can get some tips on the IF alignment.

Since I do not have any spare IF covers I'll need to drill a hole in at least one of the cans.  Before I tried to do that I wanted to see if anyone can provide advice on how to do that without damaging the can.

The other question is has anyone replaced the grommet where the cable goes into the back of the receiver?  The grommet has become very hard and is falling apart.  Any recommendations on what to use would be appreciated.  I'm considering just getting some various size grommets and picking the best fit just to prevent any damage to the cable.

Regards

Lars

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Years ago I believe I was able to use a soup can for the alignment can.  The alignment will go much easier if you can replace all IF cans with alignment cans.  Alternatively, a number of us, myself included, have blistered cans from parts chassis that can be used to make alignment cans.  The grommet is available at most hardware stores.  If the umbilical cord is not being removed and replaced, I simply cut the grommet to install.

Norman

Grommet -  from hardware store, get a black grommet same size. Break up and extract the old grommet pieces. 

Slice the new grommet. Wrap it around the set cable close to the chassis hole.

Use a moderate size screw driver, start at the slice, and carefully work the new grommet into the chassis hole. 

The start is not too difficult. But as you work your way to the other end, fit gets tighter. Proceed carefully so as to not damage the cable braid cover.

Same method works to replace smaller grommets for the small chromed round cable plugs on a number Scott models.

Norman and David

Thank you for the information on the grommets.

David has previously provided help on troubleshooting and after a long pause I'm getting back at this project.

I will give the soup can idea a try before trying anything else as I'd prefer to keep the IF cans intact if possible.

This is a radio that has been in the family since it was purchased new and about 55 years ago I replaced the electrolytics for my uncle (the original owner).  In between these years the unit has had some additional service by someone else and I think an alignment may have been attempted - I found that all the trimmers are screwed down tight and I'm hoping that with a reasonably correct alignment the BCB performance will bounce back to what I remember from 55 years ago.  

The strange thing is that on SW the performance is pretty good but while the BCB performance has improved some it still is not performing all that great -- even after recapping and changing all resistors that were out of a +/- 10-20 % tolerance.  

Again, thanks for the info and if I have any additional questions I'll post them here.

Lars

Ah yes - "all loose screws should be tightened down" mistake. Someone really went out of his way to do that.

So, starting from scratch to set the IF frequency again.

Use a signal generator ... and a frequency counter would be helpful for accuracy your IF frequency.

Start with the left rear IF coils near  the Wunderlick and work your way one IF transformer at a time towards the 1st IF transformer. Adjust one coil at a time to pass the correct IF before proceeding to the next.

It is conceivable you may need to further the adjust IF frequency if you have trouble getting dial calibration at both the high and low end of the dial.

I failed to record the AW-12 IF frequency for any of the several AW-12's I have worked on. Not in my Scott documentation. Anyone?

David

Thank you for the clarification on the procedure.

The documentation in the archives states to peak the IF transformers at 465 or 470.  It does not give the details that you have provided.

I do have a frequency meter available to verify the frequency of the generator while doing this.

Perhaps it is just blind luck but the stations that I can receive on BCB appear to be off only about 20 kHz.

I'll let you know how this goes once I get some cans that I can use to do this.



David C. Poland said:

Ah yes - "all loose screws should be tightened down" mistake. Someone really went out of his way to do that.

So, starting from scratch to set the IF frequency again.

Use a signal generator ... and a frequency counter would be helpful for accuracy your IF frequency.

Start with the left rear IF coils near  the Wunderlick and work your way one IF transformer at a time towards the 1st IF transformer. Adjust one coil at a time to pass the correct IF before proceeding to the next.

It is conceivable you may need to further the adjust IF frequency if you have trouble getting dial calibration at both the high and low end of the dial.

I failed to record the AW-12 IF frequency for any of the several AW-12's I have worked on. Not in my Scott documentation. Anyone?

Not necessarily.  If the set receives short wave stations reasonably well, the IF amplifier may be reasonably well aligned.  The default IF for the Scott Allwave receivers was 465-kHz.  If an alternative IF frequency was employed, the frequency was written in grease pencil on the inside of the back apron.  I have not seen an AW-12 or AW-15 with an alternative IF frequency.  I have seen a couple AW-23 sets with alternative IF frequencies.

Norman

Norman

Thank you.  Nothing written on the inside of the back apron so I'll work with the 465.

Lars

Yes. Also I find that is the default IF for the AW-15. So AW-12 likely the same.

David and Norman

In reference to my AW12 Deluxe AGC (S/N Y-98)

I decided that before starting any alignment I would do some additional troubleshooting relative to the low BCB sensitivity.

What I found was that there was a cold solder joint on a ground contact inside the can that has the antenna coil.  I also found that the circuit is quite different than the schematic in the archives. 

I know that Scott made changes over time and once I can trace out one more connection I'll post the schematic here. I'll be interested to hear if you have seen this configuration in the restorations you have done.

After reflowing the solder joint the BCB performance improved and was essentially the same at the low and high end of the band.

I'm hoping that once I get around to the the alignment it will perform even better.

Lars

 

Lars - The differences in Scott sets is pretty wide, especially in the earlier sets. I have always considered the AW15 a transitional set, even Scott referred to 3 versions. Recently, I've become aware of a number of variations of the AW12 as well. I'm presently restoring (for another collector) a set that is an AW12, but has an extra tube - a BFO similar to the AW15. It didn't exactly match the AW12 diagrams either and I had to draw out parts of that circuit too. I'll be interested in what differences you've identified in your set. Thanks!

Kent

Kent - the modifications to this particular unit look similar to some of the circuitry of the AW-15.

I've attached a copy of one of the AW-15 schematics and outlined the areas of similarity that I've identified so far.  I'm not sure if I'll do any more tracing.  It is interesting but my main goal is to get the unit performing good on BCB.  If that leads to discovery of more differences I'll update the information.

Regards

Lars

Attachments:

Lars -

In many ways, the AW-15 of Spring 1934 is a more developed AW-12. Scott chasing better performance and audio quality.

Beefed up amp with 2A3's instead of 45's. and 5Z3 instead of an 80.

Added 1 tube BFO to assist finding and precise tuning a station in BC and SW bands.

Modified tuning meter circuit using a tube.

Replaced single 2nd AF tube with two in P-P.

About the same receiver circuit with same tubes as the AW-12 AVC and continued Wunderlich for the first few months.

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