Help needed

[douglas wright]

Working on all wave 15, no sound or reception. Speaker rebuilt, everything good on speaker.
Looking at schematic I see primary field coil only has 5 volts going to it, is this correct? all tubes are good.
I am used to radios with higher b plus going to the field coil.
What am I missing?

[mike hadley]

Hi Doug,

5v is way to low check the continuity of your field coil windings and the connections to and from your speaker plug.

the aw15 has two field windings, one as part of the main ht filter, the other as the cathode load for the 2a3 output tubes

here is the psu schematic

the ht should be between pin four on the jones plug and chassis,

also check for continuity of the umbilical power cord between the radio chassis and the amp.

[David C. Poland]

Study the diagram closely to be sure you are measuring the high voltage at appropriate points. The B+ to the B+ field coil is just after the 30 Henry choke on the amp chassis.

And you should have high voltage at the rectifier plates and serious high voltage to ground from the rectifier filament center tap - unless the power transformer hi voltage winding is bad.

[douglas wright]

I was measuring wrong, I do have the correct b plus .speaker is making some crackling noise, but still no reception.
I can inject a signal into one of the 56 tubes and it will come out of speaker. I tried injecting signal thru antenna circuit, no results .

[mike hadley]

Is the radio dead on all wavebands?

have you checked that the local oscillator is running?

have you checked the tubes to see if they are ok?

(one of mine had a detached cathode)

did you manage to get the wavechange cam back in the correct position after removing the coil wheel?

I assume that you have changed the paper caps and checked the dogbone resistors as these have a habit of drifting high in value.

As you have checked the 56 tube then it looks like the audio stage is ok, have you tried injecting a signal to the IF stages to see if thery work you should get something even if the set is way off alignment, as I mentioned before check to see if your local oscillator is working, if you dont have a scope you can check this out with another radio, switch the aw15 to broadcast band make sure the tube cover is off of the 56 oscillator tube so you will get a little rf radaition from the oscillator position your second radio close to the chassis and tune until you pick up what sounds like a blank carrier wave, this should be roughly 455khz above your dial frequency, if this happens then the local oscillator is working and the fault is elsewhere.

Cant think of anything else just yet, any other takers?

[douglas wright]

Mike, I did test all the tubes they are ok, I did recap the majority of the radio, as far as the cam, it may not be the original, no matter where I place the cam it still wants to push the switch to short wave.  I have checked some of the resistors but not all. I checked the I.F coils for continuity, seems to check out.

next week when I have more time I was going to go back and start at the antenna coil and check for continuity and work my way forward. going back to the antenna switch i  have it pinned together on the broadcast band side of switch. i have not tried short wave yet.

[David C. Poland]

There is a cap tp replace inside each IF transformer  can across the back of the set.

Check these two switches:  I recall a wafer antenna switch - between the band switch knob and the coil wheel, just inside the front chassis apron. And the other switch inside the antenna coil can (behind of the dial) operated off the band switch shaft, located above the coil wheel shaft?

You mention the "cam". Meaning the switch inside the antenna coil can? if mounted correctly, is in one position for broadcast band  or another for the SW bands.  IMG_0980.jpeg.   the fibre cam fits a squared shaft end, but is it correctly oriented?

If the coil wheel correctly installed and not 180 degreed wrong?

Can you pass an iF test signal through the IF amp stages? audio hum if you touch the center lug of the volume control?

Curious what version model 15 you have ?   Earlier Wunderlich model with the additional pair of red antenna posts? later version as shown in Riders Vol 14 "early" or "late" - with a 55 tube 2nd detector?

[douglas wright]

My 15 is the later with the 55 2nd detector.
Also my power supply differs from the schematic, it does not have the hi/ low switch. It also doesn't have the 2 bath tub caps on the side of chassis. The cam I mentioned is in the antenna coil can.
My cam looks like someone reproduced it and may have made it too big.
I haven't tried injecting an audio signal into the I.f sections yet.
I will try that next week.

[David C. Poland]

Just to be sure, the correct 3 tube power supply uses  5Z3 and two 2A3 outputs. Sockets have tube numbers embossed.

The hi-lo switch is for the primary of the power transformer, to deal with the era's fluctuations of house voltages.

Is you switch been removed ... or is there a problem with the power transformer primary.

You should have an earphone jack in the amp, so be sure it passes the audio onto the output tube grid circuit with no jack plug inserted.

I can provide photos of the cam switch in both positions if that appears to be an issue.

[douglas wright]

One more question for you guys and then I won't bother you for a while.
What should the plate voltage be at the rectifier plates from the transformer.?

[Kent King]

I don't recall the exact voltage but it will be very high, as there is a significant drop across the rectifier tube and the filtering...probably 450 VAC...and BE CAREFUL measuring those voltages - they are AC, more dangerous than even the high DC voltages in the set. I seldom have a need to measure them, unless I suspect one side of the transformer might be open or some other (relatively) unusual problem. 

Kent

[douglas wright]

Kent. I am measuring 480 volts, with 125volt input line voltage, I also seem to be losing the 5z3 filaments not right away, just when it has been on for about 30 minutes while I am trying to measure voltages inside set.
I will have to check why this is happening.

[Kent King]

What do you meaning by losing the 5Z3 filament? Does the tube go bad (filament open)? Or something else? Does the set blow the fuse? Be sure you are using no more than a 3A fast blow fuse.

Kent