[rck46]

I'm just starting on the restoration of a 42-355. The original electromatic speaker and field coil had been replaced previously with a permanent magnet speaker. The 1000 ohm field coil in the circuit was replaced with a 150 ohm coil. Also, one 8 mfd electrolytic cap was added parallel with the original 18 mfd electrolytic and another 8 mfd electrolytic was added parallel with the existing 8 mfd electrolytic. Since I am a beginner in radio restoration I am wondering if the addition of the two 8 mfd caps is associated with the speaker replacement. If so, I assume that when replacing the electrolytics I should include the two additional 8 mfd caps. Any other suggestions will be appreciated.

Bob

[Ron Ramirez]

Hi

Most likely, the additional electrolytics were added in an attempt to reduce hum after the speaker was converted to a PM type.

However, 150 ohms isn't enough to replace the original 1100 ohm field. You should either replace that 150 ohm coil with an 1100 ohm, 25 watt resistor; add a 1000 ohm, 25 watt resistor in series with that coil (assuming it is a filter choke), or find and install the proper original type speaker.

Replace all of the paper and electrolytic capacitors, and expect to replace the old rotten rubber insulation on the wires as well.

[rck46]

Ron:

Thanks for the info. I will follow your advice. What is a good source for these resistors?

Bob

[Ron Ramirez]

Mouser Electronics.
http://www.mouser.com/

Look for the aluminum heatsink resistors, which have their own heat sink and are intended to be mounted on a chassis for proper heat dissipation.

[rck46]

I have completed the installation of the heat sink resistors to replace the field coil. Also have replaced the electrolytics, paper caps, out of spec resistors and the bad wiring. I turned it on today and am having some problems with the AM tuning. Initially I was able to receive stations in the 1100 to 1300 range but the dial did not read correctly and I could not receive a strong station around 1500 nor could I receive anything below about 1000. I adjusted the broadcast-series compensator (item 6E on the parts list and was able to receive the strong station around 1500 at the proper spot on the dial. The stations below 1500 to about 1100 still come in but not at the correct dial setting and still no reception below 1000. For example a strong staion at 1140 comes in at about 1050 on the dial. I also tried adjusting the broadcast-oscillator (item 6F) but could not detect any improvement. I need some help and will appreciate any and all advice.

Bob

[Raleigh]

If you are receiving stations strongly but at the wrong place on the dial, you'll need to do a full alignment to calibrate the oscillator to the dial. If you have a signal generator alignment is not difficult on that radio. I've done a couple of them.

If you don't have a signal generator you can do the AM dial alignment using AM stations near 1500 Hz and 580 Hz if you know their actual frequency, but you won't be able to align the IF cans properly. Do you have alignment instructions from Philco or Rider? Short wave dial alignment will be a problem unless you can find a station near 15 MHz, that you know the actual frequency of. WWV broadcasts at 15 MHz exactly if you can pick that station up.

You can approximate the IF alignment if you use a weak station and be sure you adjust the IF cans in the order 55A, 42C, 33B, 33A. The IF alignment will be approximate and performance will probably suffer, but it is better than nothing.

To get the dial alignment correct you will need to connect the loop antenna. If you have a wire antenna at your workbench for test purposes like I do, don't use it for the dial alignment because the alignment will change when you put the chassis back in the cabinet. On most radios it is hard to reach the compensators with the chassis installed in the cabinet. The way I do it is to put the chassis and the cabinet on the bench back-to-back so you can connect the loop antenna while still being able to reach the compensators from above. This method isn't perfect, but it is the only way I've figured out to do a pretty good dial alignment with the loop connected as it should be. If anyone has other suggestions how to do this I'd sure like to hear them.

I've tried the FM alignment per the Philco instructions, but it doesn't matter much since there aren't any FM stations down at the old pre-war band. If I want to listen to FM on my pre-war radios I run the audio from an FM tuner through my AM transmitter and just use the AM band to tune in my transmitter.

I don't know why, but I am sometimes able to get strong modern FM stations and TV sound from my pre-war FM radios. The sound is low fidelity and faint. I figure it may have to do with harmonics of the FM IF frequency, but I don't really understand it.

[codefox1]

Anything is possible. You can get your neighbor's ancient portable phone, a baby snoring, and instructions to the municipal water pumps and miscellaneous grandfathered "2 Way" radios on the old FM band. Like watching paint dry.

I recall this coming up a few months ago. In the 1960's there were a lot of FM to AM converters which could be used in cars to add FM reception. They were cheap. The little things received the antenna plug, and when turned on delivered the FM signal to the AM car radio tuned to ? I think it was on the higher side. Been a long time, fit one did in my '49 Plymouth and fit did, even accepted 6 volt mains.

Anyway, there have to be a lot of these still out there, and that is a possibility. I had a couple of them, but threw them out decades ago.

Somewhere along the way, I read something about a person morphing a old FM to new FM set. Never found out what he did about an updated dial display. This stuff is beyone me.

[Raleigh]

On Chuck Schwark's web site there is a link to a design for a converter that will down-convert today's FM to the old FM band. It will only convert one half of the new band at a time, because the new band is about twice as wide as the old one. You can select whether you want the upper or lower part of the band.

I think this device goes between the actual antenna and the antenna terminals on the radio, so he radio is always receiving to old lower frequency band. You run it off a nine volt battery, IIRC.

There are other designs on the web that do the same thing, some more complex than others. I don't think these are kits, so you build them from scratch based on the schematic. You might also need to wind your own coils.

I have an FM to AM converter from a car. I thought about hooking it up, but none of my radios have a phono plug, which is what you would need. I'd also need a 12 volt power supply. When I found out about SSTran it just seemed simpler to do it that way. Plus I can hook up a CD player or a computer and listen to those sources, not just FM.

[rck46]

Raleigh:

Thanks for respopnding.

I want to clarify what stations I can receive. I cannot receive any AM stations below about 1000 on the dial. The strongest stations I can receive are in the 1100 to 1300 range and the reception on these is very good. I can receive a station at 1530 that should be one of the strongest but the reception is weak. Does this situation indicate the need for alignment as you suggested?

I just acquired a Heathkit SG-8 signal generator but I don't know if the calibration is correct. Is calibration critical and how can I check the calibration? I also need instructions on how to use the generator. The generator has two switches on the left side of the panel labeled Modulation Ext or Int and AF In-Out. Also two connection points labeled AF in and AF out. On the right side of the panel there is one switch labeled RF output and another three position switch labeled RF Steps. There is one screw terminal labeled RF out and a green indicator light above it. I assume I am going to be using the RF side of the instrument. The cable that came with the generator has two alligator clips attached to the end of it. Where do these clips attach?


I do have the Philco alignment instructions and have read them several times. These instructions indicate the need for an audio output meter. I don't have one of these and is one necessary or can an AC voltmeter be used? Do you adjust the padders to get the highest voltage reading on the output meter (voltmeter)? The instructions call for the use of a loop made from a few turns of wire when adjusting the R. F. padders. What is the size of the loop?

I'm sure I will have some more questions when I get into this and appreciate the help.

Bob

[rck46]

HELP!!!!! I got back to this radio today with the idea that I would attempt an alignment as suggested by Raleigh. I did not do anything to it since my previous post. Much to my dismay the radio would not receive any stations as it did previously. Not knowing where to go next I dropped the attempt to try an alignment and decided to measure voltages to compare with the design values and report them here with the hope that someone can head me in the right direction. There are two XXL tubes and two 41 tubes in this radio. Values are shown by tube number with the design value followed by the measured value.

XXL PLATE 125 152
XXL PLATE 85 113
7V7 PLATE 187 205
7V7 GRID 75 147
7V7 PLATE 190 208
7V7 GRID 125 150
XXFM PLATE 87 133
41 PLATE 185 203
41 GRID 173 208
41 PLATE 185 205
41 GRID 190 198

Filament voltages are 6.6.

Additionally I measured the voltage across the electrolytic caps. I replaced the 18 mfd with a 22 mfd and the two 8 mfd caps with 10 mfd. Voltages are:

22 mfd, design - 290, measured - 296

10 mfd, design - 135, measured - 160

10 mfd, design - 190, measured - 208



Thanks, Bob

[Raleigh]

Bob, I've been out of town, so I didn't see the description of your additional problem until now. Have you made any progress resolving it?

From your post of July 2, it doesn't sound like your main problem then was alignment, so I wouldn't yet try the alignment I suggested UNLESS the stations you can receive are offset on the dial from their actual frequencies. Say the station you receive at 1530 on the dial has an actual frequency of 950, or something like that. In that case dial alignment is called for.

You can test your signal generator calibration fairly easily. Did you get a manual? It should have a way to do the initial calibration, since it is a kit. If you didn't get a manual, here is how I would try it.

1) Take a piece of scrap wood or plastic about 3 or 4 inches across. Size is not that important. Wrap 3 or 4 turns of wire around the wood, leaving a long lead to plug into the signal generator.

2) Connect this lead to the signal generator through a .1uf capacitor. This cap isolates the coil you have just made from any high voltage coming from the output tubes of the signal generator.

3) Place the coil you just made very near the antenna of any radio that is working properly. Lean it against the side or back of the radio if possible. A radio with digital tuning is preferable. Tune this radio to a quiet spot on the lower end of the dial, say around 600 KHz.

4) Set the signal generator on the range appropriate to the AM band. Set the signal generator output to modulated RF. Set the RF and modulation levels to the mid point. Set the signal generator frequency to about the same frequency you set on the radio. Sweep the signal generator frequency up and down around this frequency until you hear a tone in the radio. If you don't hear a tone, adjust the RF and modulation levels up, and try sweeping again.

5) When you get a tone, check the correspondence between the radio dial and the signal generator dial. Write it down. You probably have an offset, but it shouldn't be too high.

6) Set the generator and the radio to another quiet frequency near the top of the dial, say between 1500 and 1600 KHz. Sweep the generator frequency until you get a tone. Note the radio and generator frequencies. If you are lucky, your offset is nearly the same at both ends of the dial, so you can simply offset the generator reading by this amount and call it good. If the offset is greater at one end of the dial, then you will probably want to make a table of the offsets at various frequencies and use this table when you align radios so you can be fairly close.

Actually, the dials of old radios like a 42-355 don't have very good resolution, so perfect calibration of your generator isn't necessary. If you know the offset at, say, 550 KHz, then you can use the same offset for 455 KHz and be accurate enough. If anyone has a better way to calibrate at 455, chime in!

[Raleigh]

Bob, if you can't get anything below 1100 KHz, and it is not just a lower frequency station at the wrong place on the dial, you might want to check your oscillator coil and any fixed capacitors connected to it. Do the same with the broadcast antenna coil.

Inspect all the lead wires to make sure none are broken. Coil wires are pretty small and break easily but often where you can see them. Make sure you have continuity from all terminals to pin 1 on both. Note that the resistance is really low, so much over an ohm indicates trouble.

Check the tuning condenser and the compensator caps. Make sure all the solder joints are good and that you have good ground connections.

I have more troubleshooting suggestions. but I don't have the time to write them up at the moment. Let me know how it's going if you are still following the thread.

[w4rtc]

Hi bob you might check the tuning cap to make sure the plates are not rubbing each other when you turn it down to low end. Just a thought. Joe

[rck46]

I finally got back to this radio after being gone for a couple of weeks. I found my problem. The push button that selects the AM band was not working. After fixing this I was able to do an alignment and the radio is now playing quite well. Thanks to Raleigh for the help in setting up my signal generator.

Bob