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< Well I did more testing and I think I'm narrowing the problem down to the antenna transformer. Schematic says 7.2 ohms from the wiper of the volume through the coil. I'm reading 2.4 ohms .
Typically when the ant coil (primary) is bad it's open, from rotting or lightning. Check the other runs/code# of the model 38 and you may find one that matches yours.
<Can I inject sound from another source like a CD player through a capacitor at a point after the oscillator to verify?
No. If you are using an audio source you will only be able to use it to test the audio portions of the set. The mixer, IF amp, and detector are designed to respond to a rf signal. In these stages you would use a signal generator.
Reread the bottom portion of post#5 and complete the IF alignment.
Once that is done take another radio and place the ant wire or loop near the 1A6 tube. Tune the dial on the 38 to 1000kc (100 on the dial). Tune the 2nd set to roughly 1460kc. What we are doing is we are listening for the oscillator signal from the 38. In a perfect world it would be 460kc more that the dial setting. It = dial setting + the IF frequency (460kc). If it's working you will hear strong hum or hiss as you tune across it.
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: 02-26-2019, 12:16 AM by
Radioroslyn.)
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I aligned the radio. I noted the voltages to the A16 tube, attached. Still just a faint radio station that doesn't change while turning dial.
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Sorry tried attaching a picture of the A16 voltages but the file is to large. still have to figure out how to shrink it.
Looking at the tube from the bottom starting at the large filament lugs clockwise it's 0, 2v, 127.1v 124.8v .01v and 64v.
Posts: 7,301
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City: Roslyn Pa
From the looks of your voltages it would appear that the oscillator coil is bad (open winding). Should have some - voltage on the control grid (one closest to the filament). Coil has 4 connections two should show a low resistance and the other two show a low resistance too. If only two have resistance then remove the coil from the chassis and inspect it closely for green dots. This is a sign of rot (bad). Coil can be repaired by rewinding open winding w/new wire. Can go over this procedure if you with this is the case.
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: 02-28-2019, 11:13 AM by
Radioroslyn.)
Posts: 31
Threads: 3
Joined: Jan 2019
City: BARTLETT
State, Province, Country: IL
I removed the oscillator coil because I was reading 238k ohms from ground lug to the other three lugs. False alarm...it was the reading of the resistor in series, tapped at center of the two coils.
From center to a lug is 3.2 ohms, from center to the other lug 4.5 ohms. Coil looks clean. Thankyou for helping me. "I'm not giving up till the Fat Lady sings"
Posts: 7,301
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City: Roslyn Pa
Ok plan B.
Check the tuning cap for bend plates. If there is a bend one most or the time it would be one of the ones on the outside. You also use your ohm meter to measure the resistance across the cap BUT remember that it's in parallel w/ a coil that has a low resistance to start with. With that being said if it has a short it's going to be very low in resistance like something less than 1 ohm or less. Unshorted would be abt 3 or 4 ohms. Either section shorted would give you very poor reception.
The tuning cap is broken down into two sections, one section tunes the antenna circuit and the other tunes the oscillator. I don't have a chassis layout for this set only a diagram, it doesn't tell me which is which. If the cap checks out ok then I would try another 1A6.
As I mentioned before all voltages at the 1A6 look to be what I would expect except for pin 4. Should be a volt or two negative w/a high impedance meter.
No worries there is a plan C.
Happy Hunting!
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: 02-28-2019, 09:44 PM by
Radioroslyn.)
Posts: 31
Threads: 3
Joined: Jan 2019
City: BARTLETT
State, Province, Country: IL
SHE'S ALIVE !!!!!!!!!! I reinstalled the oscillator coil and this time readings were different from previously posted. There must of been a short somewhere or cold solder joint. Did an alignment and it is working. Not as loud as I would like but we're making progress. I'm going to do one more alignment too see if I can improve the volume response
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Sweeeeeet!!! the patient has regained consciousness...
Steve
Posts: 31
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City: BARTLETT
State, Province, Country: IL
I connected a 25 foot wire for the antenna it picks up only 4 of the stronger stations here. I can hear other stations very faintly Any way to make this amplify the weak stations better. I think I'm max out on the alignment. I want to thank everyone for their help plus a thumbs up to Radioroslyn.
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