Early All-Wave 12: adding a phonograph?

[Ronald Babb]

The All Wave 12 has the binding posts for a phono input.  I have read of the elaborate system they offered with tonearm and pick-up plus a microphone.  I would like to connect an RCA period correct phonograph with a magnetic pickup, horse shoe magnet type. 

How does one do this?   I believe the RCA pick-ups of this era had a DC resistance of around 75 ohms. 

Thanks!

Ron

[David C. Poland]

First, any phono on the AW-12 needs a radio/phono switch. Or you need to make one.

The radio requires a jumper ground to phono post for radio reception. (Study the circuit digram). When a phono pick-up is across the phono to ground posts, you need a switch to short  or disconnect the phono wire to restore direct connection across the phono posts for radio reception. Also, to assure no radio signal appears in the background of phono music, tune radio off station, or even turn the band switch between BC and SW position. True for early 1930's Scott radios. The first true radio/phono switch appears for the 7 knob AW-23 of 1936. For some Scott's, the phono (or CD player or FM tuner) needs its own volume control. The Allwave Deluxe AVC owners manual says no phono volume control needed, because the phono input is ahead of the volume pot so it controls phono volume control.

Scott offered a Capehart changer (Automatic 10-12, see Riders)  with magnetic pick up from about 1932-35. It has an horseshoe magnetic pickup (Scott Guide 2nd edition, pg 112). So Your RCA phono may be equivalent electrically. 

If you have inadequate volume with your magnetic pickup, then you will need an outboard preamp. There were an number of one tube preamps made by Herald, GE (and Scott, rare) and a host of 1950's era preamps with multiple inputs for phono, mic, tuner and aux. But you still ned a defeat switch to enable radio reception.

[Ronald Babb]

Thanks.  No one has done this?  I was hoping someone has?   Since this is the early set, there is no band switching, just coil changing. I suppose one could pull a coil to silence background reception?  

[David C. Poland]

Looked at your earlier posts to be reminded you have a 2-DIAL of 1931, not an Allwave Deluxe. Above all true, but you need a volume control too. Again refer to the owners manual.

I have a 2-DIAL model with Scott supplied ERLA single play phono with magnetic pickup in an ORLEANS highboy. The phono has both a radio/phono switch and a volume control to control phono volume. The phono pickup wire goes to a volume control and on the the radio/phono switch. ON places the pickup between the phono and ground OFF directly connects the phono to ground post.

For my other Scotts lacking a phono switch,  I use a 5 lug mini jack that interrupts when a stereo mini jack is inserted. Put a stereo plug on the phono audio wires. I mount the jack in a convent location with coax cable to the phono and ground posts. Then insert the plug when I want to get input from a CD player. Unplug to resume radio listening. 

[Ronald Babb]

Thanks, I’ll try it. Wasn’t sure if a matching transformer or anything else was required.

[David C. Poland]

Also, For the 2-Dial, you lack a volume control in the audio section like more recent radios designs.  So,  input into the audio circuit does require the phono have its own volume control.

You might look for an old earphone jack, of the type where inserting a plug interrupts and blocks audio to the output tube and just diverts audio to earphones. Scott's period Control Box was intended for multi purpose use and to attract revenue. 

I will photo info on the mini switch approach I use and include soon.

To minimize radio background during phono play, retard the sensitivity switch and tune off station. for a 2-DIAL.

[David C. Poland]

What I mean by a 5 lug stereo mini jack. Stereo, because it is what I could find.

See the package diagram image below. There are other sources than Radio S hack.

There are 2 internal contacts, because it is a stereo mini jack designed to keep right and left channels separate. 

But your phono is mono. So you need a stereo mini plug on the phono audio wires, connected to the both right and left. I would just buy a stereo mini jack patch cord and cut off one end, and strip back the insulation.

For phono input mode, you are inserting the phono pickup into the 2nd detector cathode circuit, by inserting the phono plug into the mini jack, braking both internal contacts inside the mini jack.

You will need a length of coax wire, long enough to go from the radio phono posts to the mini jack.

So, wire lugs 4, 3 & 1 together and to the outside braid of a coax wire, and connect to the phono GROUND post.

Wire lugs 5 & 2 together and to the internal wire of the coax wire, and to the post marked PHONO.

Thus radio plays because the cathode is shorted to ground through the mini jack.

When the phono plug is inserted, it breaks the internal mini jack contacts, putting the magnetic pickup in the cathode circuit.

mini jackIMG_1577.JPG

So wired, if you insert a stereo cable from an I-Phone or CD player, the mini jack will combine the right and left channel and play through the radio.