This is the oldest radio I've worked on so far, so it's a great set to learn on. The radio hummed when I got it and the volume control did not adjust it. I changed the electrolytic caps and all the paper caps, and I still get a hum, but the volume control now does work. I then decided to gut out and refill the bakelite blocks, which this set has four of. One problem I'm having is with the middle switch is siezed. It suppose to switch from AM to shortwave, and perhaps police as well. It does not move I have tried everything. I saturated it with 3 in 1 oil and tried working it in. Perhaps someone glued it to the AM spot, but it is not loosening. Another thing to considedr is the oscillator transformer, which I hear these sets are notorious for malfunctioning. When I use my ohmmeter, gound the black wire to chassis and test each lug, I'm coming up with 11.3 k resistance on each lug. Is that a good indicator that it's okay? I have a few 100 uuf caps coming in the mail to satisfy the last bakelite block, so there is no more tests I can do untill they arrive in the mail later this week. Any suggestions?? Much appreciated.
(This post was last modified: 11-20-2012, 11:48 PM by radiola.)
Well the best thing to do if you think the osc isn't running is to mark and then unsolder the wires on the coil. Remove it measure each winding with all rest of the radio connected to it. That way you will get an accurate reading. All of the windings should if good show a low resistance like 100 ohms of lower.
GL
Terry
Use your soldering iron on the shaft of seized control. Apply heat down near where the shaft enter the pot. Use plenty of something like wd-40 on the shaft. This will eventually work the shaft free. Don't try to force it. Learned the hard way on this. Just finished two 66's- real nice sounding radios.
Good luck.
Thanks for the suggestion. Before desoldering, I would like to do some tests, get some opinions. I did do a few tests. I used my signal tracer and clipped it to the aerial. Got just one station at a whisper. The station did not change when changing the dial. Connecting it to the 6A7 grid got just about the same except some whistling while turning the station dial. Touching the 6A7 with a soldering iron or my finger made very little noise, if at all. I'm not too savvy when it comes to coils. I've replaced a few, but never operated on any. I have a feeling I will learn through this one
Trust me it will be.
During WWII non Americans where forced to have any radio with SW coverage to be "modified" so it didn't work. I've got a mdl 81 that has a pot where the BS should and is hard wired for the BCB.
Terry
I'm not using a signal generator, however, I can do that. The 6A7 (I'st detector/oscillator) does not respond to screwdriver, finger, or soldering iron. I've been lucky with coils in the past so I don't have a lot of experience with them, however, since there is a direct connection between the grid of the 6A7 and the oscillator, it looks like I should probably remove the oscillator coil by desoldering the lugs. All agree??
Once I do that, I don't really know what I would be looking for except for loose wiring?
Continuity: I did test it and lug #2 and any other lug will yield 64 ohms. All other combinations show zero to .9 ohms. What is the oscillator trying to tell me? Thanks !!
Look at the coil carefully and determine which wires connects to which windings. Each winding should have a very low resistance like 20 ohm or less. Generally speaking most of the time the osc feedback winding is the one that is bad and will require rewinding.
Terry
The oscillator seems to be okay. I did as you recommended. There is a resistor inside which raised the resistance. I did replace the coil with a new one from Radiodaze. I'm not sure I had all the lug connections right, but it did not make any difference. I guess the next thing to do is to check the antenna coil. The resistance levels are as listed below:
A+B=6 ohms; A+c=6 ohms; A+D=3 ohms; A+E=0; B+C=.1 ohm; B+D=3 ohms; B+E=O; C+D=3 ohms; C+E=0; D+E=0; E+ground=1 ohm.
I have attached a link to the "alternate" forum, same questions. Certainly no problem with this. Might give you a little more background on Mike's problems. Good luck and maybe you can get more help here. I will state Mike again that if the coil has a resistor (10K) inside it your are working on the Antenna coil. NOT the oscillator.
Jerry
Thanks, Jerry. If you look at the picture thumbnail I have attached, there are two coils. The one on the right is the oscillator, and if you look closely, you can see a little dogbone resistor in it. Of course, perhaps they were misplaced. Thanks again. I will refer to the alternate forum.
Well first off you need to be SURE that you wired the coil back in correctly!!! That's why I said to mark the connections so they can be replaced back onto the coil CORRECTLY. They are connected in a certain order for reason if you just hook them up in any order it probably won't work. Once that is straightened out we can measure the resistance of the windings to find any open windings.
Measure with an ohm meter from resistor #10 the side that is connect to the coil and pin 5 of the 6A7.
Measure from the coil side of resistor 10 to the 800pf the is connected the the coil, the other side of the 800pf cap a connected to pin 5 of the 6A7.
Measure the resistance of resistor #15 the 32k resistor
Measure the dc voltage from chassis to pin 5 of the 6A7.
Report back.
Terry
(This post was last modified: 11-25-2012, 10:23 PM by Radioroslyn.)
Wires to oscillator are on right posts. Took before and after picture.
From resistor #10 the side that is connect to the coil and pin 5 of the 6A7. 3.5 ohms
Coil side of resistor 10 to the 800 pf that is connected to the coil. 64 ohms
Coil side of resistor 10 to pin 5 of 6A7. 3.3 ohms
Coil side of resistor 10 to 800 pf (side connected to pin 4 of 6A7) 214 K.
Also, a slight breakthrough. I found that if I connected the aerial to the grid (top) of the 6A7, I can tune in some stations. A lot of whistling and static. I can hear voices but can't distinguish what they're saying. That is with ear to speaker and volume all the way up.
Thanks for your assistance.
(This post was last modified: 11-26-2012, 09:03 PM by radiola.)
