[37silverstreak]

Hi guys,
Its been quite a while since I've posted anything here. Between getting Mom settled in the nursing home and selling her house and catching up on stuff that got put on hold while taking care of her, I haven't had much time to work on radios.
 Well I'm restoring the radio in my 1948 Plymouth, thought it would be a fun project now that winter is coming. I've recapped the whole radio and replaced most of the resistors and I've installed a new solid state vibrator and replaced the missing speaker with a modern equivalent. 
Here are the problems I'm having,
When hooked up to a fully charged 6V. battery (positive ground) and turned on, I immediately get a loud buzzing from the speaker, the tone of the buzz does change a bit as the set warms up but does not go away. I can also vary the tone slightly by rotating the tone control, but no stations are heard. I get static and clicks when touching my meter leads to tube pins, so I'm guessing the amp section is working. I tried hooking up my signal generator and I did hear a faint tone at one point. I was able to vary the loudness slightly by tweaking the IF transformers.
Also my B+ voltages are about 30 volts lower than the schematic lists. As I said I have replaced all the caps including the electrolytics using the same values.
I've just started troubleshooting and I ordered a Sams Photofact for it as the one on Nostalgiaair is kind of confusing to me and hard to read.
I'm not very familiar with old car radios so if anyone out there has any ideas or tips on what I should be looking at, I would GREATLY appreciate it! Thanks!!!!
Kevin

[Radioroslyn]

A couple of things popped out at me. Try removing the rectifier tube and turn it on. Do you still have the buzz??  If so then try removing the vibrator  to hear if that knocks the buzz out. Also noticed  that the resistance of the secondary of the output transformer is pretty high like 30 ohms. Impedance wise that's about 35 ohms. Makes me think that your replacement spkr may not be a very good match if the vc is 8 ohms.

Some of us old timers would use a separate ac power supply to get the radio working and than come back to the power supply to sort the noise issues.

GL
Terry

[37silverstreak]

Thanks for the tips. The buzzing seems to be with the speaker. I was under the illusion that this being a postwar set it would use a PM speaker, but I see it actually does use a field coil speaker. I tried a field coil speaker that is close to what I need that I had laying around and now the buzzing is gone. I can also pass a 455 kHz tone through the set, it's not loud but it's there and I can vary the volume with the control, so it's working some what. Problem is that there was no speaker attached to the radio when I got the car! I thought someone years ago had removed it, but after removing the dashboard from the car I see that the delete cover for the speaker was still installed as if it never had a radio, but there was a radio mounted in the dash. So, I don't know if the previous owner threw a radio in there just for looks or what. I haven't been able to find a correct original speaker so far so I don't know what I'm going to do. The one I'm using now needs a recone and is also too big to use in the car. Again if anyone has any thoughts, please feel free to chime in! Thanks!
Kevin

[Radioroslyn]

I doesn't look like the FC does anything but generate magnetizem for the spkr. Would just use a pm spkr. Some of the modern car spkrs have higher impedance vc than 8 ohms.

[37silverstreak]

Hey everyone,
This may be a dumb question so I apologize , but how much of a difference would it make if I were to go from a 4 ohm voice coil to say a 6 ohm one? Here's the story. I found a correct original speaker on Ebay and would like to use it if possible. The problem is that when I got it the speaker cone and voice coil were in such bad shape they pretty much disintegrated at the slightest touch. I found a correct replacement cone but am having trouble finding a suitable replacement  4 ohm 1 inch diameter voice coil. I've also tried my hand at making a replacement coil but not having much luck. I just received 2- 6 ohm voice coils I ordered online and physically they are a good fit but they are a higher value than the original. Just wanted to get some input, thanks!
Kevin

[morzh]

Well....you will increase the load by 50%.
So you will lose the power.
I think it will work ok, but the volume will go down and the full power won't be achieved. It will also move the working point of the amp so it is possible that the clipping will occur before achieving the full power.

Good news - it should work and it shouldn't blow up

[37silverstreak]

Thanks Morzh!
I'm going to take a couple of more shots at making my own voice coil before I decide to use the others. Just wanted to know how it would affect performance!
Kevin

[Steve Davis]

Kevin, You could remove a couple of turns from your new voice coils. Your coils probably wound with two layers (voice coils always have an even number of layers, two four etc.) Remove a couple of turns from each layer.

Steve

[37silverstreak]

Progress update. I've got my speaker done and it works great! Steve, I used your idea and removed some windings on voice coil to get it down to 4 ohms, thanks!
Problem is that now that I have correct speaker installed, I'm now back to having that loud hum I started out with using a P.M. speaker! It appears to be coming from the vibrator as it occurs even when I remove the rectifier tube. If I pull out the vibrator there is no hum. It also does it whether I use the new solid state vibrator or the old one that was in the set, but there is a slight change in tone on the old unit. Anyone know what could be causing this? I'm stumped !

[37silverstreak]

Another update! Radio is almost finished and is working well. Turns out that a lot of the buzzing was being caused by my using a battery charger instead of a battery (whoops!). I hooked up a 6 volt car battery and that took care of most of the noise. I was still having problems with my B+ voltages being too low until I found out that I either have a defective solid state vibrator or this set just doesn't like using one. I ended up opening up the old vibrator and cleaning the contacts and rewiring the leads and with the old unit installed in the radio the B+ voltages went to normal. Well, I say normal as in it depends on what schematic you use! I was referencing the voltage table from the SAMS Schematic I sent for and according to them my voltages were still low. I then too a close look at the Philco C4608 schematic I downloaded from Nostalgiaair and that schematic listed the voltages I was reading on my meter !!!!! Anyway, I did an alignment and put it back together. I installed a repro dial glass from Radio Daze and I just wanted to say that is a BEAUTIFUL reproduction!! They did an excellent job on it. Another neat feature about this radio is that there is tone control that changes the color of the dial light depending on what tone setting you use. There is a little color cylinder like what they used in old jukeboxes that slips over the dial light, so when you rotate the tone control it rotates the cylinder and changes the colors. It's really pretty in the dark! The original color sheet was in bad shape but I was able to make a replacement using some left over color gels I had from an old jukebox project. I only have one last question that I hope someone can tell me about. I would like to set the button presets but there are no instructions on how to do it. I know you remove the metal button cover and there is an adjusting wheel that you turn to set the station. But, my question is- do the buttons correspond to the dial scale i.e. lowest button being for the 550Khz and then preceding up to the top which would be the 1600Khz end. If anyone has the answer, please let me know! Thanks!!
Kevin

[Radioroslyn]

According to the schematic there a two coils per push button one is used set frequency and the other is peak the rf stage (Z401). Typically each pair of coils won't tuning across the whole bcb. Roughly abt 500kc so the coils that set the pb for a station at the low end of the band will tune up to 1100kc. When you go to set the pb's  the osc will be able to tune out of the range of the rf stage so you'll have to peak up rf stage as you tune the osc.

[jloban]

The push button tuning does not seem to be working as no stations are set when I use buttons and procedure to set them.  Are there points or switches that could be corroded that is keeping the two coils per PB from working?  How would I clean them?

[Radioroslyn]

Yes there are. I can see them on the diagram but I can't see them on the online pics I could find of the chassis. They're on the phenolic board near the coils. To clean would use a spray cleaner like De- oxit. Don't use any abrasives.