The Fine Things are Always Hand Made
I'm working through my AW12 and the schematic does not agree with the documentation I have been able to find.
I did find under chassis PIX of another one on the web and its the same as mine. They both look factory done Not modified.
The differences I have identified so far are:
>Sensitivity switch has 5 positions.
>There is a 4 pin female jack on the rear.
>Inside mounted just below the 4 pin jack is a small open wirewound resistor with a sliding adjustment wiper.
>The volume control is not tapped. (has 3 terminals.)
>There is a 1/4" phone jack mounted on the power supply connected between the interstage TX and the 45 tube grids. There are 93KOhm resistors from the grids to chassis return.
>The 2nd audio plate is AC coupled to the interstage TX via a .5uf bathtub capacitor mounted on the inside sidewall of the power supply.
>There is an additional small choke mounted on the inside sidewall of the power supply which is used to provide the B+ to the 2nd audio plate via pin 6 of the interface cable to the receiver chassis. (this connector has 6 pins)
Does anyone have the correct schematic for ths version?
If anyone has, or in the near future, has occasion to be in the bottom of the chassis of this version I'd be very interested in shareing some resistance measurements and tracing a couple connections.
I'd very much like to know the DC resistance of the two big chokes! One is mounted underchassis next to the sensitivity switch. The other is mounted in a can on top with the two leads coming through to the bottom and connecting in the vicinity of the Wunderlich tube and the 2 AF tubes.
Any help will be greatly appreciated!
Short answer ... Sounds like you have a "late" version Deluxe AVC a lot like mine. For example, mine also an audio choke in the receiver chassis from the 2nd AF plate to pin 6 of the Jones Plug and then to one end of the amp's interstage xfmr at the B+ feed. (Pin 6 is not used according to the diagram) And the 1/2 MFD cap between pin 3 and the other end of the interstage Xfmr primary in the amp. As tho Scott separated the audio signal from the B+ feeding the 2nd AF plate. Perhaps this improves the audio quality.
I suggest you start with a copy of the AW-12 diagram and pencil in the changes you see. You may find it helpful to better understand your radio.
All the early 1930's chromed amps seem to all have phone jacks on the amp, but the diagrams don't show it.
Always keep in mind that Scott made running changes for sake of performance. So small variations can accumulate during production. I am aware of only the one AVC diagram. So far there are 5 diagrams for the Scott Fifteen but there are variations that straddle those 5. The 12 tube Deluxe with AVC seems to have fewer variations than the Fifteen.
Have fun. - Dave
Yes that agrees with what I see. My questions are, should the interstage TX now go to ground instead of B+, and I'd still like to know the DC resistance of the two chokes in the main chassis!
Once I get the wiring verified I will post it for all to see.
Going from a foggy recollection, the reason for the late change was for the purpose of removing B+ from the interstage transformer primary and therefore reducing the risk of failure of this costly component.
Yes, I believe you are correct. My question was if the transformer should now go to ground instead of the B+.
I think it will work with one end to B+ as that end would bypass the audio to ground through the filter capacitor.
Just seems more correct to go to ground directly as the .5uf cap has already isolated you fronm the DC on the other end of the winding..
See the info at.
Looks like you have had a couple threads recently on Antique Radio Forum. Some Scott folks frequent that forum too. So, you may get additional experienced responses if you include E H Scott in the topic line.
As for the earphone jack, Scott included it on the AW-12, AW-15, AW-23 but the circuit diagrams do not show it. The jack works to interrupt the audio signal to silence the speaker when the earphones are plugged in. I never tried to diagram that phone jack.
I would keep the 1/2 MFD cap between pin 3 and the audio transformer as Scott intended.
And see my comments a few minutes ago on your other thread about voltages on pin 3, 4 and 6 of the receiver cable.
Give me your email, and I'll send you images of receiver and amp diagrams I modified to show the revisions I found in my late version AW-12.