spu/dpu jumper in stepper

Could someone pelase explain the purpose of the spu/dpu jumper in the seeburg stepper unit?

It's in the service manual--basically, it is to set the pricing .-- Ron Rich

Ok thanks ron. I'm trying to fix a unit of a friend's that was partially recapped by prior owner. Plate voltage on the 2050 is real low, and I'm trying to consider what might be going on. The big lytic c554 (300 uf 50v) has been replaced. Is there any polarity to this cap? I am not near the stepper at the moment to see if that cap is marked np. Is this cap and r556 used to keep k551 energized for added time after the pulse?

I think my friend does have some of your manuals Ron, but I'm an old retired guy and I usually forget what i read before I get out of his driveway on the way home.

The 300@50 is polarized--- and I got you beat--I forget what I wrote-- !
Ron Rich

Thanks again Ron. I know you probably get sick of answering all these questions over and over, but I might rescue a jukebox headed to the landfill someday and make it all worth while. In regard to that c554 polarity, I would really like to check the former owners work on recapping. Don't suppose you would save me some reading time at my friend's place, and tell me if the positive lead of c554 is toward or away from r556? I want to stop over at his place for a short stay tomorrow and get right at it. Figured on checking and or changing a few caps and resisters to see if I can get the stepper 2050 plate voltage up where it should be. Will probably also check the stepper wiring for shorts or anything stuck enegized that might be drawing juice away from the plate.

I was a draftee and the army made me into a radio repairman during the Vietnam era. Well as much of a repairman as you can be with 2 years service. I may have done more damage than good. I did do a little with electronics after my service days, but most of it is distant memories. My friend asked me to help him with his jukebox and it has rekindled my interest a bit. The old seeburg jukeboxes are grand machines. I've discovered that some seeburgs cost more to buy than some automobiles of the same era.

"Don't suppose you would save me some reading time at my friend's place, and tell me if the positive lead of c554 is toward or away from r556?"

ALL DC voltages in the selection receiver are positive-ground, thus all polarized caps have their positive connected to chassis common (ground).

If that 'rebuilt' receiver has already been powered and the polarized caps haven't popped they are probably connected correctly.

Rob/NYC

Thanks Ron with the maze of switches and relays in the stepper, I wasn't sure which end of c554 was aimed toward ground.

Thanks Rob rather

I get the smart guys mixed up

Thought about that stepper circuit in bed. I think some of this stuff is starting to come back to me. Looks like the 2050 works as both a rectifier and a pulse amp. It amplifies the pulse coming to it's grid from the wom blue line. Since electrons only flow from cathode to plate, it sends a negative dc pulse in search of positive ground. C552 passes the ac from the power transformer, but blocks this dc pulse. Looks like this negative pulse hits the r556 side of the k552 winding first, so I suspect the negative lead of c554 connects to r556.

The thyratron tube is not an amp, it's a switch. Granted it has a -very- narrow critical grid region where is has some linearity, but it is erratic and way too narrow to ever be an amplifier. All that happens in this circuit is that the wallbox pulls down the tube bias below the critical region and the tube fires each time that happens.

The stepper tube can be replaced with an SCR (which is what I use) or even a simple rectifier and relay though the kickback from the coils ruins the relay contacts fairly quickly.

I'm not too sure what you are getting at with the rest of your post, but I think it may be a bit confused.

The large polarized electrolytic that holds the stepper 'butterfly' coil has no direct connection to the tube or it's circuits. The butterfly (hold) circuit is established by two small sets of contacts -one set on each of the stepper "clappers'. These are the two innermost sets. Voltage is from the Low-DC rect.

The other large cap is the 5 mfd non-polarized in the 2050 plate circuit which shapes and strengthens the pulse.

Voltages in the stepper are:
Approx minus 25 vdc on the 2050 grid & approx 150VAC on the plate. Both measured in non conduction state.

The voltage across all non stepping relays is from the Low-DC rect and is approx minus 25vdc unfiltered..

One bit of friendly advice; if you don't have a schematic in front of you, it's best not to tangle your brain trying to figure out a circuit, especially an unfamiliar one. These circuits are extremely simple and once you have it actually in front of you it'll all become clear. I've been into electronics sine I was 8 in 1965 -got a First Phone when I was 17 and still pull a schematic (if at all possible) before trying to figure a circuit.

Rob/NYC

Thanks Rob. I guess my comments got you to explain the circuit a bit better to me so they weren't wasted. I did dabble in electronics years ago but have been away from it for many years until recently. I guess what I ment by amplifier is a small control voltage to control a larger power out. I guess switch fits that bill. Like an scr or triac. I knew it wasn't a sign wave amp or anything along that line. Since the electrons can only go from the cathode to the plate, I assumed it had a rectifying affect like an scr rather than full wave like triac. Since the cathode supplies electrons to the plate, I figured any resulting dc pulse or flow would have to be negative relative to chassis ground. I'm just getting going on this again, so I really appreciate your input.