I have recently acquired a number of early AC operated sets and need some advice.

(1) On an AK 40, the B+ voltage is very low, filament voltages all ok. Rectifier ok. Unit is not warm to touch. How would one check chokes or filter caps, since they're embedded in tar/wax?

(2) If unit does need to be "depotted", how is this best done? What is approximate melting point of this "stuff"? Can one melt it without damaging power supply container?

(3) Is it dangerous to put a new electrolytic from B+ to GND to see what happens?

(4) How "gold" was center of top cover on model 40, 47, etc?

(5) What is proper proceedure for aligning the ganged tuning capacitors? Do small misalignments affect radio performance significantly?

Thank you in advance for any assistance rendered!

Hi Michael

The AK40 has oil type filter caps embedded in the tar. These caps become leaky over time and will make the B+ low. You will especially notice this after the unit has warmed up for some time. The chokes are usually ok.

The power supply is built in 3 sections. The left side towards the 80 has a power transformer. The other sections contain chokes and filer capacitors. You do not need to remove the tar to replace filter caps.

I would just soften some of the tar on top with a hair dryer or heat gun. This will allow you to get to connecting wires. (If you do want to remove tar, heat the entire unit on a hot plate or oven at low temperature. Be sure to have something below the unit so tar doesn't leak.)

You can bridge the caps in your supply with a 10 mfd @ 450 volt electrolytic cap but removing the old units is more important.

Atwater Kent brought leads from each section of the power supply over dividers. You will notice wires going between sections.

There are two caps you can replace easily, one to 1st audio amp and the other detector, bottom right two terminals on the connecting board. Both of these wires can be cut lose and caps added right under the board.

You can cut other wires between sections and add small replacement caps. If for some reason all the filters can't be found, cut the ground lead. The ground is attached to one of those mounting posts for the board holding the harness going to the other section of the radio. You will see the wire near the top of these posts. Be careful as there will be two ground wires, one belongs to the transformer and must remain connected.

To remove one of the caps you will need to cut two wires and splice the ends together along with the replacement cap.

The gold top is bright gold. To find the exact color drill out the two rivets holding the emblem from the bottom. The original gold color can be seen under this emblem. Save the rivets as they can be used to replace the emblem with a small spot of epoxy on the underside of the lid.

Visual alignment of the tuning caps is usually all that's required. There are no trimmers anyway. If you want to try peaking up the signal back off the screws that hold the brass pulleys. Once this is done the variable caps can be adjusted independently. This is best done at the high end of the band. These AK's will only tune to around 1500kHz.

Norm

: I have recently acquired a number of early AC operated sets and need some advice.

: (1) On an AK 40, the B+ voltage is very low, filament voltages all ok. Rectifier ok. Unit is not warm to touch. How would one check chokes or filter caps, since they're embedded in tar/wax?

: (2) If unit does need to be "depotted", how is this best done? What is approximate melting point of this "stuff"? Can one melt it without damaging power supply container?

: (3) Is it dangerous to put a new electrolytic from B+ to GND to see what happens?

: (4) How "gold" was center of top cover on model 40, 47, etc?

: (5) What is proper proceedure for aligning the ganged tuning capacitors? Do small misalignments affect radio performance significantly?

: Thank you in advance for any assistance rendered!

Mike - check th online rider diagrams at this site. they should have some
drawings that will show you where the caps and choke are located.

follow Norm's advice for getting the caps out of the cans - they usually come out
fairle easily - but it is messy.

good luck - jim

I would have to disagree with the last comment about replacing the caps in these early sets. There are no caps in the AK 40 power supply that are over 2.0 mfd and they are not oil caps but simple paper caps....all early AC radios used these smaller filter caps until about 1930 when they rose in value. If you change the caps in these older power supplies to 10 mfd then you will have distortion due to a larger than normal increase in B+ from oversizing them so much not to mention the possibility of burning out your audio transformers! A few 2 mfd electrolytic caps will do the trick in this power supply just be sure to wire them into the circuit using correct polarity and it will be as good as new! If you have any more questions regarding early AC atwater Kent power supplies just email me at the above address and I will be glad to help you with them since I have done many of them in the past......and they still work!!! Ha Ha Ha

: Mike - check th online rider diagrams at this site. they should have some
: drawings that will show you where the caps and choke are located.

: follow Norm's advice for getting the caps out of the cans - they usually come out
: fairle easily - but it is messy.

: good luck - jim