allwave 12

[thomas higgins]

Hello:  Client asked me to work on comatose radio inherited from grandfather.  I have worked on dozens of philcos telefunkens RCAs GEs and such but this is first time tackling a EH Scott.  The turntable is a electromatic with horseshoe magnetic cartridge.  The power amp n supply chassis had no tubes and when I put some spares I had in there the audio from "phono" input came through.  Right now nothing in the way or tuned radio from its own massive tuner.  One thing I don't get is why a 9 pin mini tube was cobbled in underneath near the AF output tubes?  Might be a 12ax7?  I got the platter to turn.  I found a schematic but it is for the record cutting version which this is not.  The speaker cone is rather shot to hell.  There was a guy here in tucson that would do those but now he is gone.  Any ideas on where to send this thing?  Thank you. 

[David C. Poland]

Welcome to the Scott site.

You have the Scott Deluxe.  Judging by the 12 inch speaker ( Jensen with 2 field coils), has AVC with a Wunderlich tube 2nd detector, circa 1933. Nice looking phono. Your lowboy cabinet is the NELSON.

1930's Scotts were build upon receiving an order. The sets evolved during production, so a specific example may not entirely agree with a Scott diagram. There is more than one diagram for the 12 tube Deluxe. So, advise against modifying  to match a diagram without a careful inspection for factory original construction. Your 12AX7 would be some later modification, perhaps an attempt to substitute for the no longer available Wunderlich tube, located is 3rd tube back, far left side with a dark red button on the socket, the only tube socket with no tube number embossed on the socket. (There are some Wunderlick tubes available - it is a blue glass, interwound twin grid designed as a push-pull full wave detector and audio amplifier ). 

Information on the Deluxe model is in the Scott Info Archive at the top left of the site home page. Select Set Folders, Allwave Deluxe. 

IMG_1315.jpeg

[David C. Poland]

The Scott substitution for the scarce Wunderlich tube is a type 55 tube, with a small circuit modification. Scott radios were leading edge technology and ruggedly built, many shipped to foreign customers. Being a customer set builder, Scott could and did custom modifications of his radios. 

[Norman S Braithwaite]

The tube under the audio output tubes is most likely a phase splitter to replace the interstage transformer with a bad winding.

Norman

[thomas higgins]

The modification tube is a 6dj8 and the wunderlich tube is present and marked as such.  The needle wires have been cut.  There is a tiny transformer for the 6dj8 filament I guess and half of it is connected to the wunderlich.  Tank you for answering with helpful info.  What is the little rheostat device on far left near chassis wall?  

[David C. Poland]

Rear left apron control, is a tone control.  Is a variable resistor and cap to send higher audio frequencies to ground. 

If you mean the wire wound resistor mounted on a terminal strip inside the chassis, been too long since I had a       Deluxe on my bench, and don't recall one being in a Deluxe. Scott did use such resisters to bring a circuit into exact voltage, like in a -C bias circuit. If terminal strip is not riveted to the chassis, may be someone's modification. Best to trace it and compare to a diagram. Riders only has one diagram version of several.

Look for diagrams in Archive, perhaps in one of the factory tech documents. Most of the Deluxe AVC Wunderlich models  use only 5 of the 6 pins of the set  Jones plug, but if the 6th pin is used on yours, you have a late production model with revised audio path to amp, and I have that diagram somewhere I think. FYI - the Jensen 12 inch pedestal speaker is electrically equal to the twin speakers shown in one of the diagrams (meaning both speaker systems are interchangeable - backwards compatible).

Also, be aware if your receiver was ever returned to factory for service, Scott may have updated parts to meet later assemble specs.

Not likely to find a tube tester with settings for the Wunderlich tube. If it lights, probably OK. But treat it gently - the inside is not well supported, like all those early globe tubes.

FYI - the 3 large bathtub caps across the rear apron include a coil. They are in the cathode circuits of the IF tubes and I leave them alone, being a low voltage application. I have restored three Deluxe models over the years and those 3 caps were not a problem (nor on the AW-15). But I disconnect all the other bathtub caps and sub with modern film caps.

I have never encountered this amp without the "optional" phone jack. it is 2 position, fully inserted quiets the speaker. Just be sure the contacts are clean.

[David C. Poland]

Correction - the AW-12 diagram shows such a resistor - far left. 750 ohms  - in the negative voltage cathode circuits for the IF tubes.

Note - the phono input location to the cathode of the Wunderlich tube. When the phono pick up wires are not connected to the phono posts, then you need a jumper across the phono post to ground for the radio to work, like when it in on your work bench. Your phono should have a radio/phono switch to do the same thing when not using the phono.

[thomas higgins]

All of this helps a lot, thank you.  The switch on the phono panel provides a short across those connectors in the off position.  The cartridge wires go on there in parallel with the switch contacts.  In ON position the cartridge wires go into the circuit as you describe.  The meter has been disconnected and a short wire put on to get the B+ in to the AF circuit.  The meter reads about 1400 ohms I think so I reconnected it as a series current meter.  The radio still works but the meter pretty much stays pinned on full.  Right now I must determine how to make the cartridge work and how to get the tonearm to trip.  Manual reject command does function but at end of disk.  Underneath it looks like something is missing like a spring or clip or ??  Mine has a phone jack on the main amp and continuity is fine. 

[thomas higgins]

PS:  I cannot tell what is going on with this wunderlich; if it were dead would I have no radio?  or no phono?  It is tinted blue and no filament is clearly visible.  Might leave well enough alone as you suggest. 

[David C. Poland]

The two large Wunderlick pins are the filament. good? Continuity?

Do note that the secondary of the last IF transformer is center tapped. The ends of that secondary run to the two control grids of the Wunderlich tube. The secondary center tap feeds the AVC line back to the earlier tubes. 

A makeshift substitute for the Wunderlich tube is 55 tube with a wire soldered to the 55 tube grid cap and run down to and tightly wrapped around pin 4 of a 55 tube. That should function enough to detect audio onward. But much better to have a working Wunderlich tube. Proper substitute of a 55 tube requires a wiring mod.

Re-connect the meter if it has continuity.

Have you replaced all the bathtub caps yet ? (except the 3 large ones). Those in the higher voltage circuits leak badly in my experience. And the 3 electrolytic 8 MFD in the amp too. Modern 10 MFD work well, including  also the 1 (or 2) on the front right corner of the receiver. There is a cap inside each IF coil can too.

Also - CAUTION - follow the Factory tech info in removing the coil wheel inside. Assure the band switch is in Broadcast Band position - full counter clockwise. And do not disturb this control until you have remounted the coil wheel. Otherwise, you risk breaking the antenna switch in the antenna coil (mid chassis, directly behind the tuning dial). Careful not to loose the spring loaded buttons that act as detents when changing bands.

Also, the spring loaded contact for the coil wheel are silver plated - clean only with alcohol and a clean cotton ball.

I would not bother with the phono until you have the radio working well.

The Scott Allwave Deluxe is a very good radio when restored.

[thomas higgins]

since it is tuning AM OK and the client was threatening to gut the cabinet and put in a "modern radio" I am inclined to not go full throttle on repairs.  There is zero hum ripple and B+ seems strong though the only schematic I have lists no voltages or resistor ohm values.  I have not addressed the bathtub caps.  One was bypassed; front corner near the AF output stage.  I can certainly see if they are within specified values assuming I can determine what those are supposed to be.  With xformer coupling I am not concerned about DC leaking on to control grids and burning up tubes.  I do not intend on removing the rotary coil pack; it is making contact on all bands.  The guy really wants the turntable to work and it is turning; line level input comes through well as if it were phono so if the cartridge can be reworked, that would be grand. 

[David C. Poland]

The horseshoe magnet and coil may well be good. I had a similar type pickup in an earlier Scott that was still functional. The pickup needle "suspension" is probably  hardened rubber like material which hurts response. 

The bathtub caps are clearly marked - stamped into the metal - either .1 or .5 MFD at 200 or 400 volts as I recall. You should at least replace the few 400 volt as caps are cheap and you know what damage can result with a cap failure. That high end radio is over 90 years old.

[thomas higgins]

the magnet is still strong and the coil reads about 4K so if can get at the suspension and put something in there I should have music.  Right now I can feel zero flex on the needle fitting.  The few bathtubs I looked at went to ground on one side.  As you say it would cheap and easy to put new ones and avoid drama!