Seeburg M100C

This is my first Jukebox. M 100C. One less thing on the bucket list. Have been involved with tube radios for quite some time. I am Stan Ski over at Antique Radio Forum (ARF). Just picked this one up last week. It was working but of course had some problems. CCU would make a machine gun sound sometimes and it had low volume. Decided i would replace all the caps etc first. The guy i bought it from told me it was recapped by someone else about 15 years ago. As you can see someone only did a partial recap. The electrolytic caps were not even replaced. As i opened it up i first found that the amp has been changed . It has a MRA4-L6 in it. From what i have read this is not a problem. Correct? it has the correct selection receiver in it WSRS-L6. Looking at the bottom of the amp i also noticed something that looked like a tube added in! It was plugged into a socket. Bottom left of full size picture. It was all taped up and held in by fishing line! Pulled the tape off and this is what i found. It is wired to the 5789 tube and the PU socket (J6). So can you guys tell me what this is? I hate when i find something like this. makes me wonder what else i will find.
Stan Ski

Stan, that mess is a pre-preamp that somebody cobbled into there.
Normally, changes to the preamp section are done to increase gain to offset the lower output from either a new pickup cart or "stereo compatible" styli being used in the redhead.

The 5879 is a buffer that boosts level ahead of the second stage where the RIAA EQ actually takes place. When I modded this section I either built a single-stage transistor booster ahead of the 5879, or redesigned that stage for a 12AX7 which is what I use in the V-VL's commercially.

What you have there looks like some packaged transistor sub for a tube, possible a 6SN7 0r 6SL7. Given the amount of parts on that board it may be a phono preamp w/RIAA EQ. If so, you either have way too much bass boost or the following stage was altered. It doesn't not look like that later stages have been modified -from what I can see.

The orange capacitors should all be fine, but ALL the wax-paper caps and possibly some electrolytic's have to be replaced.

Post a pic of the mech and pickup and we can give you an idea as to how to proceed.

Do you have a service manual and do you feel competent in doing this work yourself?

Rob/NYC

Rob, Not sure by what you mean by a picture of the mech. Here are a couple of pictures of the pick up arm. As you can see it does have a red stereo cartridge in it. As far as doing the repairs myself i have restored quite a few tube radios for myself and for others. Been into the antique radio hobby for quite a long time. Have no formal training but i am usually able ( sometimes with help) to figure out a problem. Yes i have the operating and service manuals. Was able to download the schematic and parts list for this amplifier. I figured the orange caps were fine and i am going to replace all the other caps and any out of range resistors. One thing nice is there is a lot of room to install new E caps under the chassis. Not like some of the radios i have done.
Stan Ski

Hi Stan,
What chew got there, is a later "Seeburg/Pickering" stereo cart. The model C came with a mono cart. As for the "modifications" the amp,I have no clue as to why they were done. I have converted several of the mono's over like this one, never having to do anything to the amp ? Iffin I was doing it, I would set it all back to "original", add the missing 4/40 screw ( see parts book), purchase a new set of needles and be done with it --- Ron Rich

Ron, If i am reading correctly you are saying to get rid of this thing that someone installed and put the amp wiring back to what the schematic shows. Correct? Lets see if i am reading the parts list correctly. You said to replace the missing 4/40 screw. Are you referring to the missing screw on the pick up arm? If so i think that is a 4/36 screw ( 52 ) . Hope i am not sounding to stupid but the fact is i am when it comes to jukeboxes. Couple of things do not make sense to me. Why would someone install a stereo cartridge on a mono amp? Maybe the little PC board was a conversion to use it? You state for me to purchase a new set of needles. Would this be for the stereo cartridge? I am so confused but that is normal for me.

Stan, that pre-preamp is there to compensate for the much lower output of the stereo cart. The original mono cart using mono "spike" styli had an output of 30 mv max, and the stereo "T" styli cart was approx 1.5 mv.

The reasons fro converting was that the stereo cart had better sound, was able to track stereo records without ruining them and after a while, the only diamond styli were available for the stereo models, not the mono redhead.

The facts remain that the amp still needs some caps replaced, beyond that listen with new styli and decide what, if anything to do beyond that point.

Rob

Thank you Rob. Now it makes sense. This has to be done sometimes when retro fitting a new cartridge to a old phonograph. I am in the process of recapping it . At least i had the majority of caps in stock. This is going to be interesting.
Stan Ski

Stan,
That's what I would do--have change at least 15-20 of them to stereo arm/carts, without any problems that I could hear ? ('course, I am deaf in one ear and the other is plugged with wax !) Yes--stereo needles (NEW STOCK, only ! )
The screw used on the original tone-arms/mono carts, was 4-36. They changed to a 4-40, when they changed to the stereo carts.
Ron Rich

In the selection receiver they call for a 5.0 Mfd @ 300 DC Volts. What type of cap do i replace it with? Is this something special?
Stan Ski

Stan,
You replace it with the same type, if you are using the stepper, otherwise, do not bother --mounting package will be different, but they are available from "Granger", and most other motor supply houses.

Stan, as Ron pointed out, that is only for the stepper. You can use a motor capacitor, or what I have used since 1988:

http://s1192.photobucket.com/user/Rob-N ... sort=2&o=1

Those are five mylar 1mfd@250 volts. They are inherently non-polarized.

The stepper plate cap here is somewhat critical in value. I tried a 5 mfd electrolytic and had occasional miscounts. When I finally measured it, it read 6.4. It didn't foul up too often, but in location where the system gets 1200+ plays/wk I assume a fair number of people got wrong selections. Naturally, the location never mentioned anything.

Rob

Now i am confused again. Is this a motor type cap? If it is then is it used for start or run. Or is is just a good old standard mylar cap. I looked at Mousers and only found a few motor caps that were DC
Stan Ski

Yes--it is a motor run/start cap--not used for any motor, in this application.
Ron Rich

Does it have to be DC? That is what is printed on the metal part of the cap.
Stan Ski

If the original, it's an AC cap-(nonpol)---Like I said--are you using the stepper ?? Ron Rich