AW Drawing High Wattage no Signal.

[Dave]

Allwave 23 with rebuilt power supply. Plays audio. Radio isn't receiving signal and chassis is drawing close to 500w. Not sure if that's high and if so what component may be suspect ? If coil or other is open, fine, I really want to play audio thru these 2A3s ! Related to what Keith was asking below, I need a speaker and assume the field coils for these were in the 400ohm area. PM with sized output tranny and choke not that appealing, but can anyone provide the metrics for such ? Otherwise, anyone with an appropriate 12" or other speaker to sell. Need not be Scott. I know, too many questions !!

[Norman S Braithwaite]

500 watts is way to high.  Check the tuner chassis bias.  It should be -20 volts.  Loss of bias will cause the tuner chassis to draw far to much current.  The field coil was approximately 925-ohms.

Norman

[Dave]

Thanks Norman..... What is normal wattage with -20v bias ? Is this an adjustable amount ?

[Norman S Braithwaite]

The entire tuner chassis should not draw more than about 150-watts from B+.  The tuner chassis bias is not adjustable.  Incorrect tuner chassis bias indicates circuit problems.

Norman

[Dave]

Norman, you noted the speaker load was about 925 ohms below. With all the permutations of the AW23, what was the speaker impedance for the later, 1937 (7 knob micro vernier dual post antennae model) ? I can't seem to nail this down. Also, any variation for the single 12" with and without dual tweeter option ? Thank you.

[David C. Poland]

Dave -

- Appears to me you may be 1) confusing the field coil values with the voice coil values and  2) misunderstand the Scott speaker diagrams.

-

The speaker field coil measured resistance is to be 925 ohms. Regardless of what speaker you use, the 925 ohms is an important value in the high voltage circuit regardless of whether  the 925 ohm field coil of the Scott speaker - or the substitution of a power resistor or perhaps a combination of some other speaker having a field coil (provided the other speaker field coil plus any power resister needed will provide a total of about 925 ohms resistance).

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With regard to the speaker voice coil impedance, for your LATE version AW-23 receiver, Scott supplied a Magnavox speaker with the proper output transformer for the 19 ohm impedance voice coil (about 15 ohms measured resistance). The  early version speaker for the 5 knob AW-23 was a Magnavox with the proper output transformer for a 38 ohm impedance voice coil (about 32 ohms measured resistance.)

However, if you use some other speaker, you can use any voice coil impedance as long as the output transformer you select is suitable 1) for its voice coil and 2) the power handling requirements and plate load requirements the four 2A3  output tubes. Unless you understand this, I suggest you find the proper Scott speaker, either the late or early version speaker is satisfactory. Otherwise, this gets complicated - but read on ..... 

-

-There is a large power resister located in the Scott speaker's pedestal (which resistor is substituted by the tweeter field coils only when the Scott tweeters are used). This large tapped resistor is part of the bias circuit for the 2A3 grids (filaments) which are BELOW  ground potential (negative with respect to chassis ground). 

You should follow the "low frequency speaker" diagram  as though plugged into the #1 speaker socket. (Ignore the Hi frequency diagram and ignore the #2 socket). Without the proper Scott speaker, you need to replicate the tapped 5000 ohm resistor ( 3700 ohm and 1300 ohm resistors) in the bias circuit. 20 watt resistors may be large enough.

To aid your understanding, I suggest you color code  a photo copy of the entire amp and speaker diagram with attention to where the high voltage comes off the 925 ohm field coil to pin 3 of socket #1 through pin #3 of the low frequency speaker plug, and through the speaker's tapped resistor and back through pins 4 and 5 to the amp. Note pin 5 goes to ground and pin 4 eventually goes through pin 6 of the amp speaker socket and to the center tap of the 2.5 volt winding the feeds 2A5 filaments. 

Good Luck - Dave

[Dave]

As always thank you Dave for the timely advice.
I did ignore the voice coil when thinking this thru.