[morzh]

Jon

I am not sure where you typically look; I usually go to Mouser for my prototyping needs; they, Digikey and Newark (goes by Farnell in UK) are probably the three whales of electronic kitting.

http://www.mouser.com/Passive-Components...snZ1z0x1d4

These are the search results for 680pF 100V. You do not need any higher rating for the #8 cap.

[PAradiogeek]

Morzh,

I've mostly been buying from AES. All of the other pF-range caps I saw yesterday were at least 100V. For some reason, their 680pF cap was only rated at 50V. I had a feeling that that was a little low. Thanks again.

Jon

[PAradiogeek]

Hi everyone. I hope you all had a fun holiday season.

I've been (s-l-o-w-l-y) working on my 19. I have the innards of about half of the bakelite blocks replaced. A couple of days ago I decided to tackle the tone control. I've uploaded another picture to flickr and I will try to describe the problem. Here is the picture:

http://www.flickr.com/photos/104710683@N04/11894578244/

I added a text overlay identifying the tone control near the upper left. Just to the right of the tone control in the image is the on/off/bandswitch. I need to remove the tone control assembly (Item 53) in order to replace the two caps that are contained within the 'box' of the tone control. The problem is that there is a lot of stuff in the way and I can't push the assembly back into the radio far enough to get the shaft through the hole.

In the image, just under the paper label on the tone control box, there is a piece of the chassis that was bent down to serve as the mounting point for the two electrolytics. I have removed C44, the electrolytic that is closest to the tone control, but there is still a semi-circular collar that is used to hold C44 to the chassis bend-down. I unscrewed one side of the collar, but it looks like, even if I removed the collar, that there wouldn't be room to remove the tone control as the wafer/switch portion of the assembly (underneath and mostly out of view in the image) hits either the chassis bend-down, or the on/off/bandswitch assembly, or both.

Has anyone else had problems removing the tone control from a 19B (code 126)? How were you able to get this out? I thought about trying to replace the caps without removing the assembly, but I don't see how I could do that either.

Also, a related question: Assuming I am ultimately able to remove the tone control assembly, how do I get the existing caps out of the box? On a bakelite block, you heat it up and stick something through one of the top-side holes to push the contents out. This box doesn't seem to have any holes. So what is the trick there?

Thanks!
Jon

[PAradiogeek]

OK, I managed to get the tone control out. In case anyone else ever has to do it, this is what I did. I had to remove the electrolytic cap 44, the collar or strap that held cap 44 to the chassis, as well as the bandswitch. Even with all of that stuff out of the way, it was still a pretty tight fit to get the tone control out.

Once I had it out I found that the switch contacts were completely covered with oxidation or other crud so I put some Deoxit on the contacts and cleaned them up somewhat. I also started digging out the wax that covers the two tone control caps. Was getting late by this point so I stopped for the night. Tomorrow I'll finish digging out the wax and the old caps and put in the replacement caps.

[PAradiogeek]

Hey, I actually got back to work on this radio tonight. I looked in my notes and the last time I worked on it was a month ago. Been a busy month.

I placed a new electrolytic in C44 and got it back in the chassis. Then I decided to test the on/off switch continuity while I still had that switch partially out of the chassis. I removed a wire from one of the switch terminals and tested. In one position I get an open as expected, but in the other two positions, I get readings all over the map from ~3K ohms to as low as ~60 ohms.

I know I need to clean the switch, but what is an acceptable reading for a closed switch? Should it be in the neighborhood of .1 ohm, or is something a little higher acceptable?

Thanks,
Jon

[morzh]

Not sure about the 19 but in several radios like 20-70-90 the switch which is a separate entity from volume or tone control pot does not disassembled easily. Howeve what I found out is while operated under load it behaves OK while when measured with a meter it could be in kOhms range. I think the current cleans it, and if operated long enough the contacts will clean up. Of course if you can open it as in a potentiometer coupled switch, do clean it by all means.

[PAradiogeek]

After about a six week detour, I was finally able to get in several hours of work on my '19 over the last couple of days. After working on it today, I finally feel like I've turned the corner. Yesterday and today's work entailed restuffing the electrolytics and all of the associated rewiring (I.e disconnect/reconnect). I also replaced several resistors while I was at it.

Even though I try to be methodical in my rework, I had a couple of minutes this afternoon when I really thought I'd made a boneheaded move. I was double checking all of my work and all of the sudden I came across a 'dangling' wire. Whenever I remove one end of a wire, I always put a little piece of tape on the end with a notation of where that wire should be reconnected. However, there was no piece of tape on this wire. I looked over my notes because I also write down everything I do. On two separate scans of my notes I could find no mention of this wire, but in near panic I did another, slower look a through and found it.

Many people here have advised that we take photos to record the original layout and wiring. I never thought that was necessary for me as I try do only do one thing at a time and as mentioned, I write everything down. However, I now see the point of doing this. This was a very complicated section that couldn't be done one with just item at a time. Multiple components and wires were disconnected at certain points. In the end, I did have adequate notes to tell me where the wire belonged, but pictures are free and even one would have probably shown where the wire belonged. I think I've learned my lesson, because I feel like I really dodged a bullet.

Thrilled to be back working on the radio. Three more Bakelite blocks to go, and these seem to be relatively accessible. Starting to see the light at the end of this;)

Jon

[PAradiogeek]

OK, I need help, please.

I finished the recap on the radio a couple of days ago. Dim bulb test, passed. Turned radio on...nothing.
I started by checking voltages:

From C44+ to C44- => 372V
From C46+ to C46- => 300V

Field coil measured something like 1K ohms, but I forget the exact number, seemed OK.

I also checked tube voltages against the service information I got from Chuck. Here are the readings I got:
P-K voltages Measured Expected
RF 44 243 235
36 0.9 230 <=== ?
IF 44 242 240
75 233 175 <===?
42 259 235

<Edit> I tried to make a nice table here, but the extra whitespace characters are being suppressed

The 36 tube measured strange, beyond the very low number shown above. If I measure plate to chassis, I got something on the order of 240V. If I measured cathode to chassis, it was something like 9 V. yet when I measure P-K, I get .9V. What is going on here?

I probed around the 36 and low and behold, I found that the small secondary of the oscillator coil that is attached to the cathode is open. Does this explain the strange measurements I described in the previous paragraph?

Several more questions:
Does the open osc coil explain the high P-K voltage seen at the 75 tube? In other words if the oscillator isn't working, could that mean that current isn't being drawn by the IF and the detector circuits, causing the plate of the 75 to be very high. Also, the P-K of the output 42 tube is somewhat high. Could this also be explained by the open osc coil? Just wondering if I have to look for problems in the vicinity of the 75 and the 42 as well.

Does anyone have any tips on how to repair the open coil? I've never done this before. I searched YouTube and couldn't find any videos showing the repair of an open osc coil. Anyone have a link to a helpful video?

I did look very closely at these two osc coil terminals. I can see extremely thin wires wrapped around the terminals, but I swear that they do not look like they were soldered correctly (cold or non-existent solder joints). Should these in fact be soldered? I would expect so. If I try to resolder, what temperature should I set the iron to? I've read that you need to be very careful wih these tiny wires.

Sorry for the barrage of questions, but this is new territory for me. And of course, thanks in advance!
Jon

[Mondial]

The open osc coil is causing the voltage on the 36 cathode to be very high. Without the coil providing a ground connection for the cathode, the voltage will rise to the plate potential, which is why you measure little difference between P and K. The open coil is a very common problem and will need to be rewound.

The 75 plate voltage is not significant in that it depends greatly on the condition and characteristics of the tube itself. The 75 may be a bit weak, but still should work ok. In any case the 75 plate voltage has nothing to do with the open osc coil.

[PAradiogeek]

Thank you Mondial.

I have a quick question regarding the oscillator coil on the 19B. Hopefully someone knows this. In my set, the coil that is open is the small coil connected to the cathode of the 36 tube. All of the other coils ohmed out ok except that one. I removed the osc coil, but I am uncertain about which set of turns is the one I need to replace. Here is a picture of the coil,

https://www.flickr.com/photos/104710683@...277983983/

I believe it is the light-shaded one nearest the terminal lugs on the right side. This would be the bottom of the coil when the radio is right side up. Is this correct? The coil that is open connects to terminal lugs 1 and 2 if you start at the clamp that holds the osc coil in place and go clockwise.

In addition, I wanted to share the technique I used to count the number of turns on that coil. I had tried to do it by rubbing a pin across the turns, and by looking through a magnifying glass. This is probably an indication that I had too much caffeine today and I'm going blind, but I couldn't reliably count those turns. So I took a close-up picture, then displayed on my largest monitor and zoomed in as close as I could. Looking at the zoomed-in photo made it pretty easy. I counted it four times and each time the count was the same (27 turns if anyone is collecting this info for future reference).
Thanks,
Jon

[skyscraper]

Your photo link doesn't work.

Yes, that's the one, on the bottom with 27 clockwise turns. I have an 89 with the same circuit, that coil has given me nothing but trouble, be careful in your rewind or you might end up doing it again.

Good luck! As a sidenote, the RF coil primary often has the same problem. The gauge is a little lower, so it may hold on longer than the osc coil, but it will open eventually.

[Mondial]

Jon, make sure you note which end of the coil goes to which terminal, and the direction of winding. It is very important.

And Will, I have no problem with the photo link, it works fine for me.

[skyscraper]

Huh, it didn't work the first time I tried, redirected to tumblr.com. Nevermind, then

[Joeztech]

On the issue of replacing capacitors with ceramic types, always look at the specifications of the part you are considering for replacement. There are COG and/or NPO type ceramic capacitors that work just as good as silver mica capacitors for radio frequency circuits. Some are even available with negative temperature coefficients for temperature compensation in oscillator circuits (to eliminate frequency drift during warm-up). Of course many of these old radios did not bother with temperature compensation, so that would likely be overkill. Look for capacitors with not more than 10% tolerance. Most of us look for 5% or less depending on use. You can always get some good advice here on the phorum if in doubt.

Just make sure that the voltage rating of the replacement capacitor is as high or higher than the original part along with value and physical size compatibility and you should be good to go. If you are restuffing old capacitor bodies to keep original appearance, the number of possible replacements may be smaller.

Joe

[PAradiogeek]

Thanks again Mondial and Skyscraper.

I examined my oscillator coil closely this evening to try to ensure that I do the rewinding correctly. I drew a picture to help and I thought I would share, no comments on my crude drawing skills please;) Here is a picture.

https://www.flickr.com/photos/104710683@...321064493/

The wire comes down off of pin 1 and out through a hole and 'turns right' if you are looking down the tube with the terminal lugs closest to you. 27 turns later, the wire passes lug #1 and gets below lug #2 and then cuts over and across the windings up and through a hole and continues up to lug #2.

The diagram in lower right shows approximate location of the windings. The terminal lugs aren't shown, but would be on the right side of the coil form. I think the dimension to the first turn is probably the more important one, as the distance to the last turn will depend on wire gauge and how close the individual turns are to one another.

Does anyone feel that this diagram is incorrect? I don't want to propagate bad information, but I thought a diagram might be helpful to someone down the road.

Finally, We had great news today. My first granddaughter was born this afternoon. 5 lbs 13 oz. She's tiny, but adorable!

Jon