AK Model 42 Transformer Ground?

[Winky Dink]

I keep missing Kevin's posts. This is from yesterday. I will try antenna directly to grid RF2 and see what happens.

jr - No, I didn't ground the chassis to the house ground. I actually did that on the first-ever piece of electronics I worked on a few years ago. Couldn't figure out why the circuit breaker tripped every time I turned on the power. Then I read the sticker on the back panel, "DO NOT GROUND THIS CHASSIS!"

Potentiometer? I guess this is technically a pot, but I don't think they had started using that word in 1928. The wires exit the side of the Bakelite shell, and they're not accessible without pulling the chassis. The volume control apparently works properly when the signal goes through it, but the next time I pull the chassis I'll look at that.

Power transformer primary leaking to ground? Probably not, but easy enough to check.

So, this evening I'll (1) Try antenna wire to 2nd RF grid, (2) Check resistance between power transformer primary and ground, and maybe (3) Set the Model 42 up like the Model 37 using the antenna choke from the older model.

Oh, I almost forgot that I have a Heathkit signal tracer that I "restored" last year, but it's never been used. If a signal tracer would be helpful, I'll see if I can figure out how to work it.

[old_coot88]

Originally Posted by Winky Dink

Here's a recap of what the radio and I are doing:

Normal configuration on left. Configuration on right bypasses 1st RF stage.

Normal configuration, lid on, ANT post to indoor antenna:
No audible signal at max volume.

Normal configuration, lid on, ANT post to earth ground:
Receive 3 stations, some audio at zero volume, otherwise normal volume control.

Bypass 1st AF stage, lid on, ANT post to indoor antenna:
No audible signal at max volume.

Bypass configuration, lid on, ANT post to earth ground:
Receive 7 good stations and 3 weak stations with normal volume control. Only the strongest station gives some audio at zero volume.

The symptoms you've delineated here could occur if the grid of the 1st RF tube were shorted to (chassis) ground.
With the tube removed, and the coupling xfmr disconnected from the grid lug of the socket, there should be infinite resistance (open circuit) from the lug to ground. Is that what you're getting?

[Kevin Kuehn]

Originally Posted by Winky Dink

I keep missing Kevin's posts. This is from yesterday. I will try antenna directly to grid RF2 and see what happens.

You did that, only you included the volume control and antenna transformer, which is fine. I'm fairly confident there's nothing wrong with your volume control, because it seems to control the volume going into the 2nd RF stage just fine.

[Winky Dink]

Old Coot: There is infinite resistance between 1stRF grid lug and chassis ground (With no connection of grid lug to anything).

I replaced the old (magnet wire) indoor antenna with 50 feet of 14 gauge, 7-strand copper "antenna wire." It works better, and I am no longer connecting the antenna to earth ground for reception. So this is a bit of a restart which will simplify things for me.

1. In "normal" configuration, I get very weak audio at maximum volume on two or three strong stations.

2. With antenna to 1st RF grid, as below, I get slightly better audio output from the strongest stations.



3. With antenna to 2nd RF grid, as below, I get loud audio from many stations.



I've also pulled the grid resistor and the RF transformer to examine them out of the circuit, and I can't find anything wrong with them. I played with the signal tracer, but all I could do was pick up audio.

Question: With the diagram below, I still read "short" between stator and rotor. I see no physical connection of the stator with chassis ground. Is this short to be expected--is enough current conducted between rotor & stator plates to show resistance of only 4 ohms?