Just completed replacing all of the caps and resistors. Slowly powered up with my variac and after about 30 minutes checked that all voltages were good. All tubes light up but I do not have any received sound. Just a very faint hum caused by the lights in my shop. No volume or change when moving the tuning dial. I checked the antenna coil from each terminal to ground. On one side I have 6 ohms and the other is about 55 ohms. I did not see an ohm value on the schematic but from what I have read it sounds like one side of the coil is bad. Looking for advice on where to go from here.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
No problem, I don't drive so I'm around the house most of the time.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
I went back through and checked everything that I had disconnected during the re-cap. Everything is as found and traced the schematic. I rechecked voltages and they are spot on. Cleaned the volume control and checked all grounds were good. I checked the tubes with my emission tester, the output 42 is very good, one of the 77 tubes is very good and the other 77 was neutral. I still should have some level of sound other than the light hum that is not effected by volume control or ant tuning movement.
Check all of the carbon resisters values. Very common for them to drift upwards, spec is 20 percent. 10 might be a little better. Try adjusting the sensitivity (on the back apron) inward to hear if you can get the detector to oscillate. Don't over tighten as you will break the fiber adjustment nut. If you can get it to oscillate loosen about 1/4 of a turn.
Set the dial at 1000kc and listen in a portable placed near the 77 mixer tube at 1460 or so. Should hear a loud hum in the portable, you may have to tune it around a bit to find the signal. If you can't find it check the osc coil for open feedback winding.
Unplug it from the outlet. Turn volume full up. Measure resistance from the ant post to the gnd post. Should just a few ohms (10 or less) If higher ant coil primary is open.
Don't know if you know but the volume control isn't really a vc it's a rf gain control. Can't touch it to make the set hum or feed an audio signal in to it. However you can touch pin 4 of the 42, that's the input to the audio stage.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
(This post was last modified: 10-29-2016, 11:24 PM by Radioroslyn.)
I found one of your posts from 2011 about the same issue. I just checked the antenna coil. From the antenna terminal to the ground terminal the coil is showing open. Radio un-plugged and volume control all the way up.
The oscillator coil, from pin 1 to ground, 3 ohms. From 2 to ground open. from 3 to ground 2.5 ohms. (Viewed from bottom clockwise direction).
All resistors were replaced except the 1 meg. It was the only one good and was actually within 5%.
I will try the transistor radio test in the morning. getting too late tonight.
<I found one of your posts from 2011 about the same issue. I just checked the antenna coil. From the antenna terminal to the ground terminal the coil is showing open. Radio un-plugged and volume control all the way up.
That won't stop it from working, if you hook the ant to the 77 grid cap but the vc won't have any effect.
Sounds like the osc is ok but not sure abt the pin #'s. I measure from chassis gnd to the pin than has the mica cap/resistor connected to it. I think some of the later runs have a gnd pin connected the coil's mounting bracket.
Do you have a signal generator??
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
<I found one of your posts from 2011 about the same issue. I just checked the antenna coil. From the antenna terminal to the ground terminal the coil is showing open. Radio un-plugged and volume control all the way up.
When I say open, that is using my DMM on lowest range, actually switching ranges it measures 39k ohms.
Yes, the osc coil does have a ground pin on the mounting bracket. I was not counting that as a pin as there is nothing connected to it. So re-checking the osc coil, (standing at the back of the radio, up-side down, pin numbers clockwise, not counting the mounting lug) #1 to chassis ground, 3 ohms. #2 to chassis ground 6k ohms (OL lowest scale). #3 to chassis ground 2.5 ohms.
I do have a signal generator I bought a long time ago around 1997 but have never used it. It is a Precision E-200-C. I bought this at a flea market from a radio collector. He said at the time it was working, but I have yet to use it. It does power up. I did get a new test lead for it. I haven't needed it until now, so the process of re-capping that has been on hold. It most likely works just fine, but never used one. Willing to learn though!
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
I happen to have an 84 parts set so I drew out the pin connection. Resistances are from chassis gnd. Typically the one that is bad is the feedback winding which is the one on the left.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Well looks like your coil is OK but is the oscillator running???
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
I put a portable radio near the 77 tubes. The portable was set at 1460 and the radio approximately at 1000kc. There was more of a squeal than a hum and that changed with the position of the portable radio's antenna. Should I be trying with a signal generator? and at what point?
Sure why not! Connect the output of the SG to the grid cap of the 77 mixer tube. Set the SG up to produce a modulated signal at 460kc. This will tell us if the IF stage is working. If all is well you will hear a 400cy tone in the spkr. Obtw What happens when you adj the sensitivity control on the back?? With it turned up it should squeal ( go in to oscillation)
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
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