Emerson model 25 restoration

[charokeeroad]

I picked up an Emerson model 25 last week and decided to restore it. I ordered a couple new knobs that match and I'm starting to do the restoration.

I was able to pick up a schematic from the web and I started photographing and identifying the components top and bottom. I found a couple components that look like they shouldn't be there.

First off two 8mf caps attached to the speaker output coil. One attached to each of the coil leads and the other end attached to ground. They aren't on the schematic. the two shiny blue components in the bottom left of the picture.

I found another component that has both ends attached to ground. That doesn't seem right. It's the one wrapped in black tape.

The "Mite" looks like it could be C7. One end of it is in the right place but the other end looks like the last restorer was going to attach to ground. It had a lug soldered on it and was in place to be attached to the chassis with and existing nut and bolt.

The last one is show in the pictures as a long red, what looks like a wire wound around a solid core with a green dot. Not on the schematic.

could use some feedback maybe I'm missing something.

[dieseljeep]

We'll have to revue the schematic.
That is not the speaker output transformer the the newer blue caps are going to. That is the choke. This set uses a high impedance magnetic speaker, that doesn't need an output transformer.
The one mity cap is probably the cathode bypass cap for the 38 output tube.
The only schematic I find is for a model 25A, which has a floating B- line. As you noted, all the caps are going to chassis ground.
You have to do more investigation, regarding whats under the friction tape.

[charokeeroad]

I think your right. I don't have the right schematic. The one I'm looking at is for the model 25A. They're similar but not exact. I removed the black tape and took a few pictures. Guess I'll have to see if I can get the right schematic or draw out the entire chassis. My set has the optional powering plug in the back. Knowing that what I thought was and output transformer is a choke I think the two blue caps are the C9 caps shown on the 25A schematic only the C9 caps on the 25A schematic are 4mf and the ones in my set are 8mf.

Are you saying the Mite cap is the C6 cap on the 25A schematic or is it not shown on the 25A schematic? Or is it C7 on the 25A schematic? If it's C7 on the 25A schematic then I'm sure we can't use the 25A schematic as the 25A schematic shows one leg of the C7 going to the cathode of 37tube and the other going to the other side of the line input where as on my chassis the one end does go to the cathode of the 37 tube but the other end was going to be grounded to the chassis. It's hard for me to know if the previous restorer was redesigning the circuit or if the original component was attached to ground and they were just replacing what they had originally. The Mite is not and original component is it?

What was under the friction tape is the upper most red component in the top down photo it has the end painted green. Is that an original component? I don't know what it is. The long red component with the green dot below the Green end component is a mystery too. Don't think that was original either.

To add to the fun the red long cylindrical component with the green end has both lead soldered to the ground bar extension from one of the pins on the 38 tube.

The 38 tube has 6 possible connections to it none of which on the 25A schematic are tied directly to ground. The ground bar that is coming off of one of the tube pins on the 38 tube on my set is definitely going to ground. As none of the pins are numbered on the schematic it's a little hard to tell which pin is which.

Nice little radio hope I can get it working again.


Thanks for the feedback

[dieseljeep]

Let me look through some more Riders schematics. The ones on N/A are not properly listed. Will reply again later.

[Electronic M]

Those red components with paint spots on them are resistors.....The old school "dog bone" style which were OEM on most sets of about that vintage. They use the same color code as modern resistors, but you read them Body-End-Dot or "BED" for short.

Good luck in getting it going.

[charokeeroad]

So in the case of the longest one it would read:

Body= Red
End = Black
Dot = Green

2 mega Ohms ?

[dieseljeep]

Originally Posted by charokeeroad

So in the case of the longest one it would read:

Body= Red
End = Black
Dot = Green

2 mega Ohms ?

I was trying to get back to you yesterday. The resistor is R4 on the print.
I was trying to find another schematic that shows the power socket on the rear. A lot of times Riders includes odd schematics in later issues under miscellanious. That power socket was intended for an external power supply for battery operation.
Great cabinet for an entry level set.

[charokeeroad]

Is the metal looking bar a resistor?

[bob91343]

Yes it's 2 megohms. And yes that looks like a wire wound resistor.

[charokeeroad]

Thanks I think it's R6 1500 Ohms.

[charokeeroad]

I've drawn out most of the schematic. Quite a job for a little radio. None of the tube pins are numbered on the tubes or socket although I did find a way of locating the plate pin and the filaments. This set is the same as the 25A with the exception of having the seven pin jack wired in at various location to provide the optional power from batteries.

I think what I'll do is just replace the paper caps and return the set to it's schematic designated components and see if it works. I'm guessing that no one was able to find a schematic with the jack.

[dieseljeep]

Originally Posted by charokeeroad

I've drawn out most of the schematic. Quite a job for a little radio. None of the tube pins are numbered on the tubes or socket although I did find a way of locating the plate pin and the filaments. This set is the same as the 25A with the exception of having the seven pin jack wired in at various location to provide the optional power from batteries.

I think what I'll do is just replace the paper caps and return the set to it's schematic designated components and see if it works. I'm guessing that no one was able to find a schematic with the jack.

It was my thought to just disregard the external power socket. The 25A print should be close enough to troubleshoot. That radio is a real early design, using the oldest style resistors and capacitors.
The new 8 mfd caps on either side of the choke are fine as-is. I would get rid of that old rectangular box capacitor shown in the lower right corner of the first picture and install newer type components.
It's obvious someone changed the circuitry in the past, subsituting a power resistor for the original line cord resistor.

[charokeeroad]

Ok That will be a good start. One component I have not been able to find is the C3 cap that takes everything to ground. I've looked high and low but I can't find it. I'm thinking it was removed but I'll keep looking. There's a note that says it the only point to ground and the way all the grounded components are tied together at one point would lead me to think it would be there but I don't see it. It may take a bit of imagination to get this set working again but It will be worth it. I just got the knob replacements today to I'm motivated.

[dieseljeep]

Originally Posted by charokeeroad

Ok That will be a good start. One component I have not been able to find is the C3 cap that takes everything to ground. I've looked high and low but I can't find it. I'm thinking it was removed but I'll keep looking. There's a note that says it the only point to ground and the way all the grounded components are tied together at one point would lead me to think it would be there but I don't see it. It may take a bit of imagination to get this set working again but It will be worth it. I just got the knob replacements today to I'm motivated.

Disregard that cap. It never had one. The 25A has a floating B- line. The set you have, has a hot chassis, where every component that is supposed to go to B-, is going to chassis ground.
They probably did that because of the external power socket.

[charokeeroad]

I did a quick continuity check between the point where the components on the schematic are shown going to ground and one of the power input lead and was surprised to see that there is 0 resistance which I believe is what you are pointing out. It's open to the chassis.

Why do you think 8mfs were used inplace of the 4mfs called for on the schematic?


Thanks for the help