Tuning Can for Scott Allwave 15

[Michael J Boessen]

Hi, All:

My cousin from Arizona arrived yesterday at my place in Columbia, MO with a Scott Allwave 15 for me to restore.  Doing some preliminary reading, I see in the alignment instructions that there is a special IF can cover that must be installed do do alignment.  I don't have this, but I suspect I could fabricate something if I knew what it looks like.  Does anyone have one they could maybe provide me a photo and some measurements?

I have also read several posts here regarding the rotary band select mechanism, and some fairly hairy horror stories.  I would appreciate any advice anyone can give to keep me from falling into this pit.

Lastly, I have to replace some veneer on the front.  To my eye, it looks to be walnut.  Can anyone verify that?

I have already been warned that this will be a very challenging restoration, with a lot of hard lessons to be learned.  I'm hoping you guys can ease the pain a little.  This belongs to a very dear cousin, and I want to send him back a nice, properly performing radio.

Any help greatly appreciated

Best

Mike

[David C. Poland]

Any metal can will suffice. about the size of a Progresso soup can. Will need to securely touch the chassis to ground it. may need to use some tape to secure it. Or maybe someone will offer you a corroded Scott can which which you can drill out. The can coil cover is press fit, and will usually yield to rocking it. 

drill a hole about 1/2 inch in the center of the can, where the adjustment net is on the top of the coil. 

[Michael J Boessen]

Hi, David:

Soup can???  I was already envisioning fabricating something with copper sheeting and a propane torch.  Sheesh.  I'll start digging through the recycling....

Thanks!

Mike

[Michael J Boessen]

Hi, all:

Decided to start on the amp chassis while waiting for wisdom on removing the tuning assembly.  Only took a minute to figure out I don't have the correct diagram.  See attached.  I presume I have a "later" set as it has the 55 tube.  If it helps, the serial# is L-407.  The only marking I can find on the amp chassis is a pencil mark inside the chassis:  2289.  I checked my paper Riders, and it only has the one I have attached.  Given time, I'm sure I'll get it figured out, but if anyone has a later schematic that matches my set, I'd appreciate it!

Best

Mike

[David C. Poland]

That amp diagram should be sufficient. The AW-15 amp has no serial number plate. Might have a grease pen number. tube complement is a 5Z3 rectifier and pair of 2A3 output tubes. tube sockets have the tube number embossed.

Never seen an AW-15 amp diagram showing the wiring for the ear phone jack. And never seen an amp without the ear phone jack. it is a 2 step jack, first position both ear phone and speaker operate. fully inserted, the speaker goes quiet.

The AW-15 receiver evolved considerably over the 1934-5 period. The Riders diagrams labeled early and late are misleading. You will find two more earlier diagrams in the Info archive. Open set folder, then Allwave 15, Puruse the tech items too.

If there are 2 additional red antenna posts, and the 3rd tube back on the left side (2nd detector) lacks a tube number embossed, then you have the earlier Wunderlich tube set. if only one antenna post, the 2nd detector socket is embossed with 55, is later production and should be close to one of the Riders diagram.

Some Wiunderlich models were later converted to use the 55 tube when the Wunderlich tubes became unavailable.

[Michael J Boessen]

Thanks, David:

Concerning your comment about the headphone jack, the amp diagram I posted shows the headphone jack.   

I will proceed with your earlier wisdom and just replace what I find.  Mine has the 2 audio dropping resistors in a different place and a Tar potted capacitor that is not on the diagram.  Hopefully  it will still be good and I can get the values with a cap meter.  I'm sure I'll get it eventually.

My sweetheart is going to make a cherry pie tonight so I can use the pie filling cans to make tuning cans for the radio.  

My chassis has the detector tube socket marked 55, so it is the later type chassis.

I have downloaded everything from the folder on the web site, so I should be good to go.  I'll see what it says about removal/replacement of the tuning wheel.

Thanks again for the help!

Best

Mike

[Michael J Boessen]

Hi, All:

Well, I have my first major screwup, resulting from not having the correct amp schematic.  Apparently mine is a very late model, with a few additional changes.  I'm having a little trouble attaching images, but I'll do my best:

Before I go further, can anyone explain what the function of R9 & 10, and C 20 & 21 is?  

Notice the item in the amp chassis photo attached that I have annotated.  This appears to be a dual, roughly 2 hy choke.  It is placed in series with, and before R9 and R10 (see annotated schematic).  R9 and R10 are listed as 28K.  The actual resistors in the set are 14K.   Anyhow, since I didn't have the correct schematic, I traced the wiring from the downstream side of L201, part 26.  I had 1 wire going into the black can, and 2 coming out to the 2 resistors, so assumed it was a dual capacitor labeled part 20 and 21.  I heated the tar block and pulled it out of the can.  To my surprise it was not capacitors, but this dual choke.  Unfortunately, one side was either bad as found, or did not survive the removal procedure.  The other side reads 1.85hy on my L meter.  I guess, at this point I will just rewire the set to match the schematic, as I'm sure this part is unobtainium.  I kind of hate that, but at this point I have no choice.  I tried peeling back the paper in the hopes that it broke near the wire connections, but no such luck.  Hopefully, if someone else encounters this change, they will see this and not make the same mistake I made.

Best

Mike

[David C. Poland]

Thanks for the amp diagram. Was new to me - with ear phone circuit. I see it is in the Scott site  archives, in the AW-15 set folder. Been some years since I had an AW-15 on my bench.

To clarify - Early amp was resistance coupled. Later amp like yours had an interstage transformer.

Hopefully, your amp is original to your receiver.

Regarding the receiver - before you remove the coil wheel - read the tech instructions:

 -assure band switch is on broadcast band position (full counter clockwise) - pointer at 7 o'clock position.

- take a photo to record coil wheel position (to avoid reinstalling backwards on the flat shaft).

- watch for the 2 spring loaded buttons that act as wheel detents - don't loose them. 

- should be 2 nuts, tightened together to lock them to keep coil wheel tightly secured..

- do not rotate the band switch again until after the coil wheel is reinstalled - because there is also a shaft into the antenna coil can that operates a switch. You do not want to risk damage to that switch nor misalign its shaft.

-the floating contacts are silver plated - clean only with alcohol. do not scratch them. Later receiver coil wheels had felt pads to polish the silver contacts.

[Michael J Boessen]

Hi, David:

Thanks!!  I've been fooling around with everything else I can work on hoping someone could give me some guidance.  The documentation is fairly extensive, and I have a week to get this done before Frank heads back to Arizona, so I confess I didn't take the time to read it all.  I'm hoping the alignment is good and I don't have to fool with that.

I can't find anything that relates the parts on the receiver chassis underside to the schematic.  For the power/Amp schematic they are there.  For the receiver chassis I can't find anything.  I'm in the middle of trying to recap the 3 filter units marked 92, 93, and 94.  The are just marked "1/10 microfarad" like all the rest of the caps and I assumed that was all they are.  Now I have gutted them and suddenly realized there is a coil in there as well.  I need to sweat the coils out of there and then figure out how to mount them with the new cap and get them wired correctly.  It looks like the coil goes from one leg to the other, so I presume the cap  goes from one of the 2 legs to ground, but I don't know which.  Can you be of any assistance?

I know.  Bad screwup.  As grandpa used to say, "too much hurry, and not enough think".  That said, I have everything else under the chassis finished, except one cap under the wheel.  I'll start on the coil cans tomorrow.

Really appreciate the help and patience.  Quitting for the evening.

Best

Mike

[David C. Poland]

The larger bathtub caps across the back apron of the receiver do also have a coil inside. Being in low voltage circuits, I don't replace nor rebuild them unless there is a problem detected later after powering up the radio.

My experience on the AW-15 is substitute modern caps for the other little bath tub caps. And the caps in the IF transformer cans. Yes, I unsolder the grid caps from the grid wires to the IF tubes, to be able to fully remove the press fit chrome covers. And mount new 10 MFD filter caps on a terminal strip in the amp, leaving the top mounted caps in place for appearance. (they will polish up almost like chrome with Mothers Mag Polish from the auto supply department). Then I power up with a Variac to about 90 volts and take voltage readings. as a way to find any other problems.  The radio may well play at 90 volts AC, and after a few minutes, advance the Variac to 120 volts and check voltages again to detent any out of tolerance resisters that matter.

[Michael J Boessen]

Hi, David:

OK.  Thanks!  If I had not gutted 2 of them I would take your advice and leave them.  The caps on the 2 I gutted are both good.  I still haven't figured out where they are on the schematic, but eventually I will.  I see a red dot on each of them.  It looks like that terminal has the coil and cap on it, with the coil going to the second terminal and the cap going to ground.

Appreciate the help.

Best

Mike

[Michael J Boessen]

Hi, All:

If  you've been reading this thread, you know I gutted 2 of the filter units, numbered 92, 93, and 94 on the attached diagram,  thinking they were just capacitors.  I always drill a small hole in the back before sweating the cover off to vent gasses, and destroyed the coil on one of them.  I'm new here and not sure if this is ok, but if anyone knows of someone who has a AW15 parts unit, I would buy 2 of these filter units.

Thanks!

Mike

[David C. Poland]

I recall those 3 larger bathtub caps across the rear apron of the receiver are in the cathode circuits of the IF amp 58's. Kent would have those bathtub caps in his chassis boneyard.

As for parts layout in the receiver, look at the AW-12 folder - aka Allwave Deluxe. The AW-15 evolved from the later "AW-12 with AVC" using the Wunderlich tube. The primary improvements for the AW-15 is:

- revised 3 tube amp for more audio power with 2A3s.

- addition of a BFO circuit using 1 tube.

- revised tuning meter circuit adding a meter amp tube

- adding a 56 tube to change 2nd audio stage to 2 tube push pull driver.

- and finally, later in 1934, abandoning the Wunderlick detector in favor of the 55 tube for 2nd detector.

Always remember, Scott was a custom set builder. Each AW-15 was built upon receiving an order:  was then built, tested and shipped in 3 to 5 weeks. Scott was capable and willing to further customize the radio for the buyer.

Scott was chasing performance, and so there were numerous small changes during the production run, more so for the Aw-15 than any other 1930's Scott. Riders published two receiver diagram. There are 3 earlier diagrams in Scott Info Archives. But correspondence among Scott collectors several years ago revealed 7 versions based on actual variations of features, tube complements and control functions. When confronted with a specific example, may find it straddles 2 diagrams in detail.

So, exercise restraint trying to make a receiver agree with a particular circuit diagram. Inspect connections and leave original solder joints alone as legitimate. Also, prudent to discover the seeming actual IF frequency adjustment first before alignment, because Scott might use another IF frequency than published for reasons unique for that buyer or chassis.

I found it fun to explore the differences in various examples of a particular model Scott. Good Luck