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

[Lars Edwards]

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

[Lars Edwards]

With the repair of the cold solder joint and some minor adjustment to the alignment the BCB performance is now quite good.

The next on the list is the tuning indicator.

When the radio is off the needle is on the left.  Once the radio is on the needle moves to the right and then stays stationary regardless of the strength of the station being received.  In watching this closely there may be a slight wavering of the needle when tuning through a strong station.  From what I can see without taking anything apart is that the needle is bent quite a bit.

Any advice on how this should respond normally, what I might look at next and how to straighten the indicator needle without damaging it ?

Thanks for any info

Lars

[David C. Poland]

The meter pointer is indeed quite small, not much bigger than a wire. 

In mounted position, the action is lateral. So the pointer is bent down to enable the pointer to cast a shadow on the dial.

With mine, when powering up the radio, the shadow appears from the left and moving right rapidly and comes to rest at the near edge of the broadcast  band graphics. Tuning a stronger station, the shadow moves to the left towards the SW scale graphics. A weak station produces little meter action. The stronger the station, the further left the shadow moves towards the SW graphics. 

The meter is on a stalk, so adjust the stalk with regard to the dial lamp so the meter shadow plays within the edges of the dial strip.

This is 1932 technology. To improve action, the next model (model Fifteen) added an amp tube to the meter circuit.

[Lars Edwards]

David

Thanks again for the info.  I removed the movement and straightened the pointer somewhat.  However, there is still no movement of the meter to the left when tuned to a strong station. 

One thing thing I can think of to try is to use a signal generator and connect it to the antenna terminal to see if the meter will move and change as the level of the generator is changed. If not I'll have to dig deeper.

Lars

[Kent King]

Lars - The signal generator idea is good - you can create a very strong signal to see if the meter reacts. As Dave noted, the 12 doesn't have great meter action and Scott added another tube to increase the responsiveness in the 15. Still, you should get some movement on stations, I wonder (since the indicator was bent) if it may be dirty. You can remove, dismantle and clean the meter <very> carefully.

Kent

[Norman S Braithwaite]

The primary cause of poor tuning meter response is IF alignment.  Scott radios are well known for being able to pick up stations even though the IF is not well aligned.  In such cases the tuning meter will have anemic operation.

Norman

[Lars Edwards]

Kent and Norman

Thank you for the quick replies and the information.

Once I have a little time I'll check the response of the meter with the signal generator and after that take a look at the IF alignment.

Lars

[Lars Edwards]

Just an update:

I finally got around to checking the tuning meter using a signal generator.  I connected the generator to the antenna terminal and set the receiver and generator to 700 kc.  With the generator at minimum output I gradually increased the output of the generator looking for the meter to move to the left but it did not move at all.

After turning the radio on the meter moves from left to right and stays there. There is no deflection when tuning a strong station or with the signal generator connected.

After I get around to the IF alignment I'll see if I can get a response.

Lars

[Kent King]

If the meter moves when the set powers up, it is ok. Meter action is not as strong on the AW12 sets but once the alignment is done, you should see some action. 

Kent

[Lars Edwards]

Kent

Thanks -- I'll update after I get a chance to do the alignment.

Lars

[Lars Edwards]

I have finally got around to starting the IF alignment.

I finally found a reasonably priced tool to neatly cut the holes in the top of the IF cans and got that done this week.

I also made a tool for the adjustment of the trimmers.

After an initial pass on the IF alignment (by ear) at 465 kc the performance is much better.

Underneath the chassis there are two cans (with holes for trimmer adjustment).  There is no mention of these in the alignment procedure.  My thinking is that these also need to be part of the alignment process - does that sound correct ?

The needle indicator is still not working correctly and I'll get back to that once the IF is finished.

I also have a question about the antenna tuner.  Any recommendations on where I can find knobs for this ?

Again, thanks for any assistance.

Lars

[David C. Poland]

The SW antenna tuner uses the same knobs as the front controls. Ditto the rear tone control if your receiver has a rear tone control.

[Lars Edwards]

David

Thank you for the information. Is there a source you know of for reproductions or replacements?

Regarding the IF alignment:

1st the IF circuits are similar to the AW15 in that there are trimmers underneath two of the IF transformers that must also be peaked.  I'll do the alignment following the AW15 instructions.

In the beginning of looking into the IF alignment I found the trimmers screwed all the way down (plates closed all the way).  I think I may have found out why.  What I've found is that the 1st IF has a very broad peak and peaking at 465 is not possible - it is closer to 475-480 kc and that is with the trimmer plates as tight as possible on both the top and bottom trimmers.

Performance is reasonably good at this point.

The trimmers on the  IF's trimmers have a good bit of adjustment left when I peak at 475-480 kc.  The dial calibration seems pretty good - within 10 kc pretty much across the AM band- but probably could be a little better.

I'll be looking at the 1st IF in more detail to see if there is anything that can be done to improve that situation.

As always any suggestions are welcome.

Regards

Lars