[winkydink]

I have recently had several of my tube radios recapped.

several 42-PT95's a 48-200 and two 46-200.

the 42-PT95's work like a dream and are very easy to tune stations in and have excellent sound.

One of the 46-200 and the 48-200, have a hard time tuning stations in without distortion. It is almost like an oversaturation of the signal. One has to be so precise to tune a station in and the tweek the dial in very small increments. Still even at best there is still distortion.

I though that this might be something unique to the 200's but then one of my other 46-200 behaves like the 42-PT95's and is very easy to tune in the station.

Does anyone know what this is caused by. Is it an oversaturation of signal, or does the tuning need to be adjusted some how.

Please understand that I am an absolute novice, trying to learn. I know there is a way to fine tune, but I don't have any special equipment to do this.

Any help, suggestions etc would definitely be appreciated.

[winkydink]

I have done some reading and watched a few youtube videos about IF Alignment.

As stated above, my radio's symptoms are that very strong stations have the audio distorted. Talking sound the best, but is still somewhat distorted, music sounds very bad, unless I move the dial off the strongest signal, and then it sound better but still distorted.

Could this be a problem with regard to the IF bandwidth. In other words perhaps the IF bandwidth is too small and thus the edges/lobes of the signal on both sides are getting clipped and thus the distortion.

Just looking for some possibilities here. Any suggestions would of course be welcome.

[Arran]

Did you, or whoever worked on these sets, go through and check the resistors as well as changing the capacitors? It could also be a wiring error caused by misinterpreting the schematic, if it was worked on by the same person, usually distortion of the sort you describe is caused by an open bypass capacitor though a misalignment could also be an issue.
Regards
Arran

[winkydink]

Arran,

I did not do the work myself but rather "farmed" this out to a company Atlas Audio in Pittsburgh PA. I know that the capacitors have been replaced (paper and electrolytic). I also believe that the resistors were tested and replaced if found bad.

I do not believe they changed any of the wiring, and the radio looked like it had all original components in it before any work was done.

I am not really sure what a bypass capacitor is (one of the paper capacitors ?) So I really don't know about that. This is occuring as stated before on 2 radios that are essentially the same (46-200, 48-200).

I have contacted Atlas Audio to describe the problem, and have given them a link to this thread. I am awaiting a resolution from them,but would also appreciate any ideas from forum members.

[Arran]

One other thought, are the speakers in the two sets in good shape? Like if you press on the cone evenly is there any rubbing noise?
As for the bypass capacitors, yes they are usually paper caps, there is a large one that goes between the B- and the chassis, in Philco sets there is also a coil in series with it, if this is left out the set will howl and motorboat. There may also be a few others that run between various things and the B-, B- is what some call common negative.
Regards
Arran

[Chuck Schwark]

Also be sure the built-in antanna loop is connected correctly AND that it has continuity. If there is an open loop, AVC voltage will not get to the front end tube and the gain will run wide open also causing the exact distortion you have. Also check all the components in the AVC buss as well as the 150K resistor at the loop.

The AVC voltage also goes to the IF tube grid for gain control.

Chuck

[Arran]

Chuck has a good point that I did not think of, and it is a problem I have run into before myself. Those loop antennas have fairly thin wires and it isn't unusual for the wire at either end to break off on the secondary winding where it is soldered to the chassis or the antenna section of the tuning condenser. In fact on many of these late 40s Philcos the loop antenna is glued onto the inside perimeter of the cabinet, you really have no choice but to disconnect it to get the chassis out, and there are four wires coming off of it, two go to chassis ground (not B-), one goes to the tuning condenser, and one is the external antenna connection. If this is the case then they would have had to disconnect the loop antenna to remove the chassis in both sets, this my be why both appear to have the same problem.
Regards
Arran

[winkydink]

Here is my update:

I tested to see if there was any shorts in the antenna loop. Unfortunately I couldn't tell. I used a multimeter (even watched a youtube video), but results were unsatisfactory.)

When I touched probes together the meter went to zero. When I attached to each end of antenna wire. Meter stayed at infinity. But wait. Then I attached to antenna wire 1 inch apart from each other , still at infinity. So I can't trust the results.

I then "made" a new loop antenna. (made a cardboard shell that had same circumference as inside of radio cabinet ). Looped wire around 19 times (the same as the antenna inside the cabinet).

Results, garbled sound (worse than original antenna).

Then I connected the radio back to the antenna inside the case (soldered it back onto the connectors). I then did a realignment.

I tuned the radio to a weak stations and moved the screws 1 at a time to peak the volume. Result: The reception was alot better. I am going to play the radio for several hours to see if it stays this way. But although not perfect, I can definitely hear a difference.

Stay tuned.

[Chuck Schwark]

Testing the loop was for an OPEN, not shorts. If you measured only a couple ohms or less, then the loop is good. I assume your disconnected one end of the loop to isolate it before you tested it, otherwise results may be invalid due to connections in the radio.

Sounds like it may still be out of alignment then from your re-tweeking. I'd also test for continuity of the IFT's, both pri and sec windings.

Chuck

[winkydink]

I Thank you for the suggestion, I have it better but not perfect.
I am not an expert, I don't understand the terminology being put forward. I am coming from a background of computer science and working on old phones, which is vastly simpler that radios.

I have no electronics background, but have a healthy respect for electricity and alway try to be safe (Isolation Transformer, Variaac etc)

Some of the suggestions here, I simply don't understand what exactly you are suggestion. Perhaps that means I should be doing this type of work, but I really would like to learn more about working on these type of radios, just under a safe enviorment.

For example the following suggestions, I don't even know where to begin with regard to them

As for the bypass capacitors, yes they are usually paper caps, there is a large one that goes between the B- and the chassis, in Philco sets there is also a coil in series with it, if this is left out the set will howl and motorboat. There may also be a few others that run between various things and the B-, B- is what some call common negative.

Also be sure the built-in antanna loop is connected correctly AND that it has continuity. If there is an open loop, AVC voltage will not get to the front end tube and the gain will run wide open also causing the exact distortion you have. Also check all the components in the AVC buss as well as the 150K resistor at the loop.
[AVC is Automatic Volume Control ? I have no idea as to how to check components in the AVC buss and the 150K resistor at the loop. Is there a part of the schematic that shows AVC buss ??? Again, real new to this and the terminalogy, schematics, etc are killing me]

Those loop antennas have fairly thin wires and it isn't unusual for the wire at either end to break off on the secondary winding where it is soldered to the chassis or the antenna section of the tuning condenser. In fact on many of these late 40s Philcos the loop antenna is glued onto the inside perimeter of the cabinet, you really have no choice but to disconnect it to get the chassis out, and there are four wires coming off of it, two go to chassis ground (not B-), one goes to the tuning condenser, and one is the external antenna connection. If this is the case then they would have had to disconnect the loop antenna to remove the chassis in both sets, this my be why both appear to have the same problem.
[Yes, this has the loop glued into the inside of the case, and you do have to unsolder to get the chassis fully out. There are 4 wires coming off of it ???? I only see 2 ]

I'd also test for continuity of the IFT's, both pri and sec windings.
[what is continuity, what are the primary and secondary windings ?]


I really appreciate the help, I am trying to look up as much terminology as possible, but I am lost as to what some of these things are that you want me to check.

[Chuck Schwark]

Sorry, IFT is short for Intermediate Frequency Transformer, or more commonly, IF Transformer. Check continuity of both transformers, primary and secondary windings in both transformers.

Chuck