EH Scott Radio Enthusiasts

The Fine Things are Always Hand Made

Hello and Happy New Year !

I am new to the group and just getting started on repairing/restoring an Allwave 12 to operating condition.  The serial number is Y-98 and it has a Napier cabinet that is in fair to good condition.  It has the single large speaker and all the old electrolytic cans on the power supply and radio are still in place.

As far as I know the radio has been in the family since it was purchased and in the mid to late 60's I installed new electrolytics in the power supply only for my uncle and it worked well for a lot of years.

The last time I powered it up, approximately 20-25 years ago, it worked but had a lot of hum.

The main goal here is to get the radio functioning first and then decide if I want to tackle the cabinet.

My strategy is to replace all capacitors in the power supply and the electrolytics in the receiver first then check the power supply, check the radio and if it works at all then replace capacitors and resistors as necessary.

I have pulled a schematic from the archives to use as a guideline.

One question I have is regarding the large 0.1 MFD "bathtub" capacitor assemblies (#8031) that also have a coil (located on back of receiver chassis with red dots).  I have read the information on how to open these up and restuff with a new capacitor and that seems pretty clear.  My question is has anyone determined how to duplicate the coil ?

Any suggestions and information are more than welcome.

Thanks and best regards.

Lars

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Here is an update on some additional progress.

Using spare 58 tubes I started substituting according to the guidelines in the AW-12 literature.  What I found was a nice improvement when 2 of the 58's in the IF were replaced.  I also found that one of the 58 spare performed better in the RF.

The BCB reception is better and consistent at the high and low end of the band.  The calibration is good across the band as well.

One thing is a bit puzzling.  Before doing the tests with the tubes the antenna trimmer on the tuning capacitor peaked quite sharply and the RF trimmer tuned very broadly.  Now it is the opposite.  The antenna trimmer now tunes very broadly and the RF trimmer peaks very good.  Looks like more work may be required here.

Any suggestions are welcome.

I also replaced a couple more resistors that were out about 20%.

Before I start opening the IF cans does anyone know the value of the capacitors in these?

Thanks

Lars

The latest update is that I substituted some of the spare tubes that I had (58 &57) and improved the BC reception in particular at the low end of the band.

I restuffed one of the coil capacitor combinations (on the back wall of the chassis) with a new capacitor.  This gave additional improvement so now I'll do the same for the other two.

Lars

Yes - I recall a cap inside of each of the IF coil cans along the back of the receiver.

All 3 have been recapped.

BCB reception is a little better but it is still on the weak side.  At night I can now get some distant stations such as Cleveland, San Antonio, Chicago at my location here in north Alabama.  The signal strength is on the weak side but at least it is working and the performance across the band seems to be the same. Dial calibration is very good.

I'm using an antenna that is ~ 65-70' including feedline.

One thing I've noticed is that adjusting the antenna trimmer on the tuning capacitor gives a very broad peak.

SW reception is excellent.

I have not tried to open up the IF cans yet.  My rationale was that if the SW reception is really good then the IF alignment is probably ok but maybe that is not the case ?

Thanks in advance for any suggestions !

After a very long delay I'm back on this project and have opened up the IF cans.

The printing on the tubular capacitors in the IF cans is hard to read but it looks like they are .025 mf @ 400 V.

Can anyone verify that this is the case ?

I don't plan on replacing the mica capacitors in the IF cans but just in case can someone provide the value(s)?

Many thanks !

My Scott factory AW-12 diagram says .025 MFD 400volts for the caps in the IF transformer cans.  A cap close to that value should be ok, but don't scrimp on the voltage rating - I used 630 volt rated caps. I have never had to replace a mica cap in a Scott.   ... The mica are 100 MMFD per that diagram.

Daytime verses nighttime reception. Nighttime is when the ionosphere (reflective layer) forms and radio signals  reflect allowing long distance reception (not consistently) especially for the Broadcast band and some SW bands. Many low power BC stations sign off around sunset because regional high power stations travel greater distances and interfear with reception.  Generally, stations at the low end of the dial seem stronger. 

Hence, here in central OH daytime is limited to local stations. I barely get the big daytime 500,000 watt stations of WLW Cincinnati,  the big Chicago stations, WSB Atlanta  or WABC New York. But I get them all well at night. Even the big stations vary at night due to ionosphere conditions, electrical storms, interference from adjacent stations, etc.. Your Scott will make the best use of any signal received.

David

Thank you for the info on the components.

The resistors in the if cans will also be replaced.  The actual values range from 700K in the 1st IF to 600K in the 3rd IF vs the 500K value indicated by the color codes.

In this area I can get 3-4 AM stations during the day. The local AM station (2500 watts) about 5 miles away is the strongest signal during the day.

In the evening the reception of AM stations is not very good. There are a few of the higher power stations that come through but the signals are weak.  I'm hoping to get to the point that I can get WGN & WBBM in Chicago clearly due to their old time radio programs.

I do have my communication equipment (ham radio, call sign KA4U) that I could use but that is not the same as listening on the Scott or any other vintage radio.

Again, thanks for the assistance !

Hello David

Again, thanks for the help.

I received the new components Saturday and installed the new capacitors and resistors in all 3 IF cans last night.

I just tested the AM band and it is much better now.  The local AM station is "booming" in and I could actually hear (very weak) WSM (50K Watts) in Nashville which is about 90-100 miles north of us plus a few other local stations at useable volume. Total antenna plus feedline is 50-60 ft.

My Radio Shack DX-390 does not get any signal for WSM during the day but I do not have an external antenna attached.

All the stations I could receive on the AW12 are tracking accurately across the dial.

Tonight I'll be interested in seeing what the performance is like.  If I feel it is good enough I'll probably skip the alignment of the IF.  So I'm very encouraged and keeping my fingers crossed.

Hi David

Receiving a lot of AM stations at night now!

Now to work on some of the other details.

To me it looks like someone previously messed with the tuning indicator. It is bent up pretty bad and moves to the right when the radio is turned on but stays on the right side.

As long as you can see the shadow of the tuning meter pointer, it is useful to precisely tune in the station for best tone and signal. The meter pointer is indeed small gage wire, so the shadow is thin. My meter pointer shadow extends down about half way to the horizontal shadow.

As my AW-12 first powers up, my pointer shadow first swings into view from the left and settles about in the middle. As a station with some strength is tuned in, the shadow moves to the left towards the KC markings. The stronger the signal, the greater the shadow deflection to the left.

Placement of the dial lamp (small round) in the grommet and angle of the meter stalk allows some left/right adjustment of the meter shadow falling on the dial strip.  

(The AW-15 and AW-23 tuning meters are wired differently than the AW-12 AVC receiver).

Hope this helps.

David

Very helpful.

Again thank you !

The question I have now is what is the correct bulb # for the AW-12.  The one in this AW-12 is apparently not correct.  It is rather long and definitely not a small bulb.  Looks like someone substituted one that they had handy that just happened to work.

The total length of the bulb is 1 1/8".  The base is 1/2" and the oblong bulb is 5/8" long.

When screwed into the socket about 1/4" of the base sticks out of the socket so the bulb is positioned very far to the left.

Using my illuminated magnifying glass the only marking I can see on the base is MAZDA.  I strongly suspect this is the wrong bulb based on your comment.

If the bulb was much smaller I think I might be able to see the needle of the meter.

If you confirm I do not have the correct bulb I can get some and then try straightening the needle and bringing it into view.

In regard to your advice on the power supply voltages they are very similar to the ones you mentioned in your reply yesterday. So from that perspective I think things are in pretty good shape. 

In the power supply/amp I am having some difficulty identifying a couple of the components because I can't seem to find a schematic for this "pin 6" version.

Under the chassis near the hi-low switch there are two smaller black metal enclosures (~ 1" cubes).

Can you shed some light on what these are ?

One appears to have a single lead and the other has 2 leads.

Again, thanks so much for all your help

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