[Caperodder]

Hello Folks,

Pure amateur here, and my first old radio, so bear with me.

I'm working on a Philco 60 that I acquired, that has not worked in over 40 years. The previous owner had "worked" on it and made several schematic wiring errors, including two dead shorts, not to mention poorly chosen component values. It's a 1935, so I'm working from the December 1st 1934 schematic. I've since recapped the radio, and painstakingly matched the wiring to the schematic. Went through the proper procedures of using a variac and dim bulb tester. Low and behold, she powers up. Volume is working properly as is the tone control. Other than a couple of foreign stations, on either setting of the band switch, I am not getting local broadcasts.

This is where I can use a little help. One thing I noticed that the previous owner had done, was to run a ground wire from the chassis to the frame of the tuning capacitor. It looked home brew to me so I left that wire off. However, after first turning on the radio, I received absolutely nothing until I added a test lead, and once again grounded the capacitor. Should this be grounded? I have installed new rubber grommets under the capacitor, and it is clearly isolated from the chassis.

I had purchased a NOS and tested 6A7 tube, so I'm starting to think that one of the coil windings on the antenna coil may have an open. Correct assumption?

I don't have a way to test the 78 and 75 tubes just yet, but since I'm receiving foreign stations, I'm targeting that coil. Make sense to anyone?

Thanks much,

-Brett

[Chicago Jimmy]

Ground it!

[Radioroslyn]

I didn't look at the diagram but most sets the isn't grounded to the chassis. Usually it is isolated from the chassis via rubber washers and what you will have is a screw that is holding the cap in place with a solder lug on it. That will connect back to the avc buss. If that is not in place the set will not work. If you ground the tuning cap the set will work but without avc action.
Terry

[Phlogiston]

I didn't look at the diagram but most sets the isn't grounded to the chassis. Usually it is isolated from the chassis via rubber washers and what you will have is a screw that is holding the cap in place with a solder lug on it. That will connect back to the avc buss. If that is not in place the set will not work. If you ground the tuning cap the set will work but without avc action.
Terry

A lot of radios have bothe the rubber washers AND the ground(s).

[Ron Ramirez]

+1 what Phlogiston said.

I've never seen a Philco that had the frame of the tuning cap isolated from ground and tied to the AVC bus instead. Every one I can recall at present from 1931 on had the tuning cap mounted on rubber, but the frame was still tied to ground, either by a wire soldered to a rotor connection on top (in sets such as the 70, 90, 71, etc.) or by one or two wire braid straps with one end soldered onto a tuning condenser mounting bolt, and the other end connected to the chassis, usually with a rivet.

In most Philco superheterodyne radios, AVC was applied to the RF amp (if used) and the 1st IF tube. Many Philcos did not have AVC applied to the mixer stage, although some did. And there are a few that did not have AVC on the IF stage, or if more than one IF stage, there was no AVC on the second IF stage.

In the Model 60, AVC is applied to the mixer stage as well as the IF stage - but the AVC goes through the secondary of the antenna coil, on the stator of the antenna stage of the tuning condenser, to grid 4 of the 6A7. The stator is the stationary, ungrounded part of the tuning condenser, which is insulated from the frame. The rotor is the part that rotates (hence the name rotor), and is physically connected to the tuning condenser frame.

[Caperodder]

Thanks everyone.

Ron, the braided wire you describe is exactly the part I left off. It was soldered to one of the screw heads that hold the tuning capacitor to the chassis. When I saw that, I figured that there was no way it was factory installed part. I was wrong. I've since put the strap back on.

I can only receive 2 foreign stations at the far end of the dial in either band switch position. Looking at the antenna coil I'm finding that I have 11.1 ohms from the top of the coil winding to lug 5, (across the 10k resistor on the band switch) but 17 Meg ohms between lug 5 and ground. Does that mean that the .7 ohm winding is at fault? The other coil associated with the 6A7 tube is showing 34 and 47 ohms as per the schematic. I'm going crazy figuring out this circuit. Measuring the secondary side of the antenna coil next. (1.0 ohm, 5.5 ohm, 1,0 ohm)

Thanks,

-Brett

[Radioroslyn]

Bet you don't have any voltage on grid 2 of the 6A7 (pin 4)?
Terry

[Caperodder]

Hi Terry,

I have two different 6A7 tubes, one supposedly new. The filament is at 6.4V They read as follows:

(old tube)

2 - 287V
3 - 96V
4 - 208V
5 - 31.2V
6 - 2.3V

(NOS tube)

2 - 291V
3 - 100V
4 - 188 V
5 - 42V
6 - 2.4V

I soldered the ground strap back onto the tuning cap as described above, and can now get some weak signals on the BC band. Static increases as I climb the dial. The radio is grounded, and I'm using about 10' of antenna.

-Brett

[gvel]

Bret...it does look like the antenna coil is open. Make sure you have a good ground connection, at the coil, though. If it is open, it's fixable, but I'll let others elaborate. I've never done this.

Place your wire antenna lead on the grid cap of the 6A7. Your radio may come to life.

[Caperodder]

The coil has been suspect from the start (mostly because they are notorious for having opens). When I first began the restoration, the top coil lead was broken from the terminal. That has been re-soldered, and I was hoping for the best. What I'll do next is unsolder and remove it from the radio for inspection. I've always been intimidated by winding one of these, but if needed, I will proceed. Ive read a bit about them on other threads and other forums. Direction and number of turns and wire gauge seem to be the most important factors.

If I need to do this, I will likely open a new thread with a more appropriate subject title.

Thanks,

-Brett

[Radioroslyn]

Two things come to mind. As Gvel mentioned connect the ant to the grid cap of the 6A7. If the coil is open the set will play well with this set up.
2 Unplug the set and connect an ohm meter from the ant post to the chassis. If coil is good you will read a low resistance like 10 ohms. If it is like a 1000 ohms it's time to rewind.
Terry

[Caperodder]

Hi Terry,

Ok. Added the antenna wire to the grid cap of 6A7. Still getting only 2 local stations, very faint. Noise increases dramatically as I tune up the dial.

My meter is telling me 30 Meg ohms between the antenna clip and ground.

-Brett

[Caperodder]

With the antenna coil on the bench, hopefully some helpful measurements:

1. Top of coil to lug 5 - 11.4 ohms
2. Between lugs 2 and 6 - 6.9 ohms
3. Between lugs 1 and 5 - open
4. Between lugs 3 and 4 - 5.1 ohms

Looks like the .7 ohm winding between 1 and 5 is open. I though that would only effect the SW band and not the BC?

-Brett

[Ron Ramirez]

OK, now we're getting somewhere. The 0.7 ohm section is the "police" band primary. However, since it is in series with the AM band primary, if the 0.7 ohm section is open the radio will not work properly.

This 0.7 ohm section is 4 turns of 38 gauge wire would on the outside of the coil form, down close to the solder lugs. The 4 turn section will be easy to rewind.

[Caperodder]

Hello Ron.

Well that explains things. Can I simply use Kapton Tape as my insulator at the base?

Remove the wax with a heat gun, or will that destroy the enamel coating?

Hoping I can find some 38 gauge wire. Once wrapped, shellac the coil to hold everything in place?

Thanks again,

-Brett