Starting work on my 19B - Printable Version
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Starting work on my 19B - PAradiogeek - 12-06-2013
Hi Everyone,
Well I have finally started work on my Model 19 Code 126. I pulled the chassis from the cabinet and started getting oriented with the underside components. All I can say is... I've entered some sort of bakelite purgatory
But seriously, I have two questions:
First, there is one component under there that I do not even begin to recognize. Here is a picture of the underside of the chassis. I have circled the component in question near the upper right.
http://www.flickr.com/photos/104710683@N04/11231240073/
Can anyone identify this for me?
My second question is a real noob question. I don't see any way to identify which pin is pin 1 on these tube sockets. On other radios, I have seen a gap between pins that was larger than the others, or there was a key in the center post of the tube socket. I don't see anything like that with these sockets. Can someone enlighten me as to how to identify pin 1?
Wish me luck on this restore. Hopefully I don't botch it.
J
RE: Starting work on my 19B - BrendaAnnD - 12-06-2013
Your mystery part looks like a coil.
As for tube socket identification, this is simple.
Look at your sockets. You will see that there are two larger pins on most of them. Picture these larger pins as being on the bottom looking at the socket. As you do this, start from the left hand one of these larger pins, this is Pin 1. Each pin going clockwise from there is pin 2, 3, 4, etc.
The exception to this is the 5 pin tubes. If you look at those, you'll see they are in a sort of pattern like a baseball base, with pin 3 being the pointy end of the base. Counting counterclockwise from this, you have pin 2 and pin 1. Counting clockwise from there, you get pin 4 and pin 5.
RE: Starting work on my 19B - Mondial - 12-06-2013
Yes, as Brenda said the mystery part is a coil. It is the IF transformer between the 39/44 tube plate and the 75 detector diodes.
RE: Starting work on my 19B - PAradiogeek - 12-06-2013
Brenda, Mondial:
Well I learned my thing for today. I had pretty much decided that it was going to be a cap of some kind.
I also appreciate the tutorial on pin 1 identification. This is my first set from the early 30's, so not yet familiar with these tubes/sockets.
Thank you both for your help.
J
RE: Starting work on my 19B - PAradiogeek - 12-11-2013
OK, after a few days of delay I removed the first Bakelite block. It is the one in the upper left corner of the picture I posted above. I was able to find the the information on what was contained inside in the tech section of this site (thanks Ron). I was able to extract the existing cap and replace it with a .047 uF 630 V cap. But I have two questions:
1) I know this is probably a 'personal preference' kind of question, but do people generally re-stuff the Bakelite blocks with the black wax or some other compound? If another compound, what do you recommend?
2) Some of the resistors in this radio are large and some are huge. They look like they might be 5 watts. For example the 2K ohm roughly dead center in the picture and the 39K (the orange one) a little to the right of that. I don't seem to have a parts list that gives me power ratings for the resistors, so how do I tell how big (in watts) is big enough?
Thanks in advance.
Jon
RE: Starting work on my 19B - BrendaAnnD - 12-11-2013
1) It IS a personal preference. I used to repot mine with a hot glue gun. Others, including myself now, don't bother to repot them.
2) The "HUGE" resistors are generally 2-3 watts.
RE: Starting work on my 19B - PAradiogeek - 12-12-2013
Thanks Brenda.
The guy I bought this radio from had tried to get it working, but he was not successful. There is a sticker on the back of the chassis that says the rectifier caps were replaced in Feb. 2003. What are the chances that they are still good after sitting on the shelf, unpowered, for the last ~11 years? I'm fine with replacing them again, but I only want to do that if all you experts think this is a good idea.
Jon
RE: Starting work on my 19B - BrendaAnnD - 12-12-2013
11 years isn't bad, as long as the caps have not been damaged, e.g. reverse polarized.
RE: Starting work on my 19B - codefox1 - 12-12-2013
Well depends on when replacements were done did.
RE: Starting work on my 19B - morzh - 12-12-2013
Today's electrolytics can sit on a shelf for a while but long term storage degrades the aluminum oxide and so a capacitor stored for years has to be reconditioned.
This, according to, for instance, Panasonic, requires application of the rated voltage via 1k resistor for 30 miunutes. Otherwise restoring current may become too large and damage the capacitor.
http://www.panasonic.com/industrial/components/pdf/aluminum_app_dne.pdf
This said, I would not worry about capacitors in RC filtering circuits, but those in rectifier filters, especially the first one, right after the tube, should be paid attention to. And the other one after the choke also.
RE: Starting work on my 19B - PAradiogeek - 12-13-2013
Thanks everyone.
Morzh: Would running the set with a dim bulb tester for 30 minutes work for the purposes of reconditioning the electrolytics, or would you recommend inserting a 1K between the rectifier and the first filter cap (and then later removing the resistor)?
Jon
RE: Starting work on my 19B - jerryhawthorne - 12-13-2013
I give a ++ to Brenda, why pot the bakelites? Just stuff them and remount. The potting adds no value as to how long they will last. No one can tell the difference.
Jerry
RE: Starting work on my 19B - klondike98 - 12-13-2013
Jerry Wrote:The potting adds no value as to how long they will last....and not potting them makes it a lot easier for the next restorer to replace those caps
RE: Starting work on my 19B - Radioroslyn - 12-15-2013
You may be able to damage the new cap with the heat from the hot glue. Those little yellow caps don't like heat. More work with no benefit.
Terry
RE: Starting work on my 19B - PAradiogeek - 12-15-2013
Looks like the nays have it as far as re-potting the bakelite blocks. Thanks everyone for sharing your thoughts.
Does anyone have advice about my question above as to whether a dim bulb tester could be used to recondition an electrolytic cap? My guess is that this is probably not a good idea as there is nothing limiting the current between the rectifier and the cap, which is what a series resistor would do. I did want to get people's thoughts though.
Jon