M100C Capacitor replacement question

I have started the task of replacing the paper/electrolytic caps in my M100C. I started on the Selection Receiver chassis (it had fewer caps, so figured it would be easier). I am down to the last cap, C-4. I know which lead is the positive lead (center one) for the capacitor, but my question is: does it matter which negative terminal on the old can that you connect the negative terminal of the replacement cap to? There are 4 different terminals that I believe to be the grounded side of the can (the 4 terminals around the perimeter of the bottom of the can, 3 are in use on is not). I will leave the old can in place and connect the positive side of the replacement cap to the wire that is currently connected to the center post of the old can capacitor (I will disconnect old capacitor + terminal), but can I connect the neg. side of the cap to any of the other grounding terminals on the old can?

I did learn a hard lesson about this little task that I would like to pass on. There are several deviously installed caps on the credit unit. If you decide to disassemble the credit assembly to provide easier access to these babies, be forewarned, the click you will hear are the spring driven pawls that will make your day miserable if you did not look at their original position prior to removal of the last screw. 45 min later it now works correctly....ugh, what a pain.

Thank you in advance, Craig.

Craig,
Short answer--yea--any "grounded" lug--
Longer answer--I usually jump any that I use to the original grounding point--
Ron Rich

Will do Ron and thank you again.
Craig

Replaced all the caps, very meticulous about orientation of electrolytic caps and only replaced one cap at a time to ensure a one for one replacement. I clipped the old caps off close to the cap. This left me some wire, which I made into a small loop, to which I soldered the replacement cap to. I did not want to de-solder most pins due to multiple components connected to the same location. This way I was able to avoid introduction of multiple problem connections. I also checked every solder joint I made to verify continuity from the cap wire to the original terminal through my solder connection. To make a long story short, I was careful. However, after all this care, the bloody thing does not work.
The speaker puts out an extremely loud hum and there is no amplification of the music. I researched possible causes and improper electrolytic installation was usually the cause. I double checked and triple checked the orientation of all the electrolytic caps and they are all attached to the correct terminal in the correct orientation, though this took a lot of tracing of wires. I have pulled the 6SL7 tubes and the 6L6 tubes and still got the hum. The hum volume does not change when the volume control is manipulated. It did stop when the Rectifier tube was removed (as anticipated). The mute control functions properly, since the hum does not start until the record and stylus are in place and playing the record.
I have removed the power caps (cans) C-1, C-2, C-3a,b,c and checked them again (they were checked before installation too) for the proper value with a capacitance meter. The C-1 and C-2 caps that were supplied with the kit were larger than the originals, but my research found that this is OK and can be better for performance. The C-1 provided was a 100 mf(tested at 100)/450volt, the original was a 60 mf/350volt. The C-2 provided was a 47 mf (tested at 50)/450volt, the original was a 40 mf/450 volt.
I verified a good ground from the center tap of the transformer (strange grounding setup through the speaker plug as shown in the schematic). I sent and audio signal through the grid of the 6L6 valve 7 grid (clipped cap C-27 grid pin connection). I had a 12" permanent magnet type speaker connected to the voice coil, which transferred the hum from the internal speaker to the speaker I had connected. The audio signal was then introduced but was very difficult to detect through the speaker over the hum. I am a bit bummed out and need some help troubleshooting this problem.
As a note of importance, this jukebox was producing decent sound but did not have much volume prior my meddling. I guess on the plus side it the hum is much louder than the volume before I recapped the jukebox. I have tried to teach it to hum a song, but it is not the least bit interested. Thanks in advance, Craig

When you formed a 'hook' in the old component leads, did you swab the old leads with alcohol to clean it before soldering? The old leads can have a build up of wax, nicotine, grime, dirt, etc that can prevent proper soldering.

I have pulled the 6SL7 tubes and the 6L6 tubes and still got the hum

Then you don't have good ground on the center tap. I ran into this several times on those old amps and I remove the C-T and solder it directly to chassis. What is happening is that you are seeing a good ground via ohmmeter but are actually reading through the speaker voice coil- output tran secondary to ground.

Rob/NYC

Craig,
I would jump the speaker plug SOCKET, with an alligator clip lead to start--those are known failure points, that often cause this problem--Power OFF, when doing so ! If that "don't do it", jump the transformer connection to chassis, as Rob suggested. If still a problem, jump each power supply connection--something's not "making good contact". Ron Rich

If the issue is "hum while playing a record" did anyone consider bad grounding of the tonearm/input/assiciated wiring?

Hi Matt,
Good point--the RCA input plugs often fail to ground--EZ check should be to remove that plug when playing a record. ( Audio is muted, by a switch, in between selections, so no hum, would be heard---). Ron Rich

Been "accessing brain info" (OK--thinking about this)--
Not being able to hear the "hum"-- I have heard/seen other things causing "hums--squeals", on these amps-- Check the wire going to the top of the 6J7 tube--this s a drain, not a ground, so "the ground" can not be connected on both ends. I have seen people attempt this--I have also seen the drain dis-connected on the chassis side, and I have seen where the cap is not making a good connection. Also check all tube sockets, for a "poor" connection-- just "wiggle" the tubes with power on, while playing a record. Also, have seen "bad" 6J7 tubes, that will cause all sorts of "hum" problems. Ron Rich

While attempting to ground the center tap through the speaker plug, in my excitement in testing for the various solutions, I jumpered pin 4 to pin 5 (ground) instead of pin 6 (xformer center tap) to pin 5 (ground).
Yes, I screwed up and I am very frustrate with my error. Looking at the small pin numbers while laying on the ground, holding a light and using magnification, somehow #4 and #6 got confused....nuts.
This caused R-1 to fail. I have tested the low voltage coil and it still shows good continuity through the winding's and no short to ground, I also tested the tubes and power caps (lucky the caps supplied are rated at 450 volts) and they are still good. I hope I dodged the stupidity bullet, but is there some other component that I may have destroyed that I should check prior to applying power (after I obtain and install a new R-1).
Thanks again for your help and I will investigate further when I find a replacement resistor. Hopefully there is an exact match available.
Craig

Craig, you won't have damaged any audio tubes or caps, there is a chance that the 5U4 is ruined or the power tran is killed -but both are fairly rigged. I've had shorts in filters kill a fuses on location and both tube and tran were Ok afterwards. For a quick 'n dirty test just attach a meter to the first filter at the 5U4 and apply power. if B+ builds, shut down and walk away happy.

The resistor shows as 1200 ohm @10Watt you can use anything that gets you close (1K to 1.5K).

Rob/NYC

Update on repairs.
Rob, I was not comfortable testing the transformer under power until the resistor replacement, was a bit gun shy after my last error.
Matt, I unplugged the tone arm plug prior to trying the jumper idea again and it did not correct problem.
My replacement resistor finally arrive and after replacement I jumpered the center tap to ground via the speaker socket. I jumpered the correct pins this time with a 2nd and 3rd verification prior to energizing. The Hum has been banished! Can I permanently jumper the speaker socket (pin 6 to pin 5) for a permanent ground? Those pins are currently jumpered inside the speaker plug, but the connection is less than adequate or none existent at this time. They may have grounded the center tape via the speaker plug to avoid excessive voltage through the affected circuits if the speaker (load) was unplugged during jukebox operation (just a guess), otherwise its a goofy way to ground the transformer.
As I mentioned the hum went away, but I forgot to mention so did the sound. All the tubes were replaced with new ones upon completion of the recap of the amp. Ok, next up Ron I tried wiggling, after working up a sweat I reread your post and tried wiggling the wires. While twisting the tone arm connector (RCA type plug), amplified music was again flowing from the speaker. Since I have no past experience on how loud this M100c should be, I am guessing they were not extremely loud by current standards.
After listening to the initial 4 selections play for the 2nd time I realized a new demon had possessed this old girl. The sections were not clearing. Prior to the recap the selector had been clearing the selections. The troubleshooting guide mentions cleaning plunger and coil, possible open coil, short to ground in cancel coil circuit, misadjusted switch contacts. Since I dinked around in the contacts to replace some caps, I guess I will start there and update the progress when there is some.
Thank you again for everyone's help, Craig.

I'm glad you've banished the hum. Yes, the goofy arrangement was to prevent the application of B+ if the speaker was disconnected. While there are good reasons for this, at this point those old plugs are going to cause more trouble than they are worth so I wire the C-T directly to ground.

The low volume may, or may not be an actual problem. If the amp has been properly rebuilt the main culprits are styli and speaker and volume control plugs. You can try rocking those plugs while a record is playing. The original redhead w/mono "spikes" were radically louder than all the later stereo compatible types. If you have a black cart on that machine, it might need to be rebuilt as the damping is no longer holding the armature properly in the flux field.

It is also possible that the output tran has shorted turns. In general this will manifest itself with reduced bass and low volume which becomes distorted when the amp is pushed. If you have a signal generator and scope this is an easy test. If not, there is only substitution of the tubes and tran as an option.

Hopefully it is just styli or connections.

Rob

As for the speaker jumper--I have heard many "reasons" for this--but I wonder, as Seeburg abandoned this arrangement for the last two, or three tube type amps the built. I still hesitate to bypass this, so, I use Deoxit on both the plug and socket, as directed on the can. This works well, on 99 % of them. If it does not work, I take a dental tool ( the kind the mean lady uses to torture me, when "testing pockets" on my few remaining teeth), and carefully "re-form" the socket pins.
As for volume--no, they do not have the volume to hurt your ears--but if the switches are correctly set, the AVC is working properly, you are using good needles ( for the "Redhead", which are once again, thankfully, available from many of the suppliers listed above), they should be rather loud.
The selection non-cancel problem has nothing to do with the amp--see the troubleshooting guide. One thing NOT in those guides, is, the cancel pins, tend to become "sticky". If this is happening on both sides, check to see if the pop meter coil is working. If so, suspect "sticky" plungers. If not ( providing the pop coil is connected), check both coils to determine if the coil sleeve has become loose. If the C-SC contacts are adjusted correctly, you will hear a "bezit" sound as the needle sets down on the record. This sound should be no longer than it takes you to pronounce the word above. If longer, you WILL burn up the cancel coils ! If you just get a "bizz" sound out of it, the pulse is too short. Once correct, I strongly urge a 1/4 amp SB fuse be added to the circuit. Ron Rich