[Jeff Lepore]

see
Hello again! I've got a crazy problem with my philco 38-7 CS. Ive changed all caps, checked all resistors,  checked continuity on antenna coils, and changed a couple tubes. The set plays great when I run a wire from the tuner condenser to the antenna wire not the terminal.  Or I touch finger to tuner. Many say it's it's grounding issue or antenna and oscillator.  Any thoughts. Set sounds great with this setup. I tried to add a photo and video. It said image to large and video was the wrong kind. Never had this problem before. Finally got an image to attach. set goes dead when I unhook clip

[RodB]

Hello Jeff,

What you are doing with the antenna wire, or your finger, connected to the tuning condenser is bypassing the antenna transformer and some contacts on the A wafer of the bandswitch (range switch). So I assume you have checked continuity on both the primary windings and secondary windings of the antenna transformer. You can try heating the wire connections with a soldering iron. Barring a wiring error, that leaves the contacts of the switch. Maybe you have cleaned them but you can hit them again with Deoxit.

[Arran]

I would have a go at resoldering, or replacing the grid cap lead on the 6A8 tube, it might be breaking down. This is a problem with double ended tubes with grid caps, input grids are low voltage, low current so any problem with the solder joints, or breaks in the wire, wire will cause problems, I've fixed a number of tube battery radios this way.
Regards
Arran

[RodB]

Arran,

I assumed the grid cap runs from the tuning cap to the 6A8, so if he touches the antenna wire to the tuning capacitor and gets good reception that would eliminate the grid cap as a problem. Though it's always a good idea to double check the grid cap being they have such a reputation.

[Jeff Lepore]

Thank you guys so much. I rechecked all solder joints, continuity on the antenna and oscillator coils, and used deoxit on the band switch and volume controls. Removed the alligator clips and plugged her in. And bingo, stations were everywhere coming in loud and clear. It’s been a pain trying to figure this out. But yet so satisfying when you bring an old radio back to life…. Thanks again
Jeff Lepore

[MrFixr55]

There are 2 antenna terminals and one ground terminal. Make sure that you are using the "red" terminal. Note that the "black" terminal goes to ground for some strange reason. Maybe the diagram is misdrawn. However, even if misdrawn, in broadcast band, the black lead is grounded. Ohm between the red terminal and ground. You should have continuity. Resistance is less than one Ohm.

Try using an external ground, preferably a water pipe ground. When hooking up to the antenna side of the coil as opposed to the tube grid / cap stator side of the coil, a complete circuit is required to cause the "transformer action" needed to cause the signal to pass through the secondary.

[RodB]

We should all be cautious about how we use the term "ground". Back in the day the GND on the back of the radio probably meant an "earth" connection to a cold water pipe. As we can see, this often means connecting the chassis to earth ground. Or does it mean connecting earth ground to the chassis?

[MrFixr55]

Hi Rod,
I agree that the term "ground" may be confusing, and wish that the electronics industry and the antique radio community had some sort of standardization.

In the case of the radio in this thread and almost all transformer powered sets requiring external antenna and ground connections, the ground connection is the return of the antenna transformer primary, and happens also to be the chassis. Since this is a transformer powered set, the safety of connecting the chassis to an earth ground is not an issue (transformer leakage and the line filter Death Caps notwitstanding).

What I find to be more confusing and potentially dangerous is defining the common return of circuits such as B-, the low side of a series heater string, etc., which is commonly referred to as "ground" but certainly is not. In a warm chassis set, the chassis is not this common connection. In a hot chassis set, the chassis can at a level 120V (in the US) above ground depending on the power switch state and the "polarity" of the power cord. Connecting a "ground" to AC-DC sets must be done with great caution and only to such connection as stated by the manager. Some AC-DC sets had external antenna and ground connections through either a transformer or through a winding on a loop antenna. I have never seen an AC-DC set where an external ground to the chassis was allowed, due to the aforementioned issues.

What Europe refers to as "Earth", the US NEC refers to as "Ground". In radio practice, historically, a ground connection was made to a cold water pipe if available, or to a radiator. The NEC has traditionally required bonding of the service entrance and the "neutral" conductor to the cold water supply to the house at a point very close to that entrance. For a rather long period of time, the NEC also requires a second "made ground" of varyig methods, the most common being a ground rod of at least 8 feet driven into earth material whose composition and moisture are conducive to creating a ground. The NEC has very specific nomenclature for hot, neutral and ground conductors, which I forgot and do not have a document handy. The existence of non-metallic water pipe allowed in recent plumbing codes complicates the issue.

Of course, in automotive electrics, the term "ground" is used to describe using the auto body structure as a common return conductor. (In most US cars built 1956 or later, the "ground" is negative). Of course, where is the "ground" unless your kid tracks dirt in the car or that bag of potting soil that you put in the trunk broke open.

I have tried to use the terms "Return" B- Common or "Mecca" to refer to those points indicated in the schematic of an AC-DC set using the traditional 3 line arrow shaped ground symbol.