Too much bass on Seeburg J

I hope someone can help me with this problem. Recently, my Seeburg J amp (MRA5-L6) went out completely. I had never recapped it, (as I know I should have), but I did at that time. I recapped the entire amp and replaced the resistors that measured out of spec. I also, had to replace a couple of tubes, including a 6J6. In fact, I replaced both 6L6 tubes at that time, although only one was bad. I have the amp back in the machine now, but the sound is terrible. I cannot control the bass. By that I mean, even with the volume down, it sounds like it is overdriving the bass to the extent it distorts the sound. Both bass intrument sounds, as well as bass vocal sounds are distorted. They appear to be too loud. In fact, so loud and strong they vibrate the entire jukebox. It does not matter where I set the bass and treble controls, as they have no affect at all on the sound. I have tried with the AVC on and off, with the 6SK7 tube in and out. There is no difference, or if there is, only slight. Of course, I can turn the volume really low and it helps, but the bass is still distorted. I did not have the bass distortion problem before the amp went out and I recapped it, so I have to believe it is all associated with either the amp failure, a component replacement, or a tube. Can anyone point me in the right direction, as to what to check next? Thanks for the help in advance.
Julian

Handyman62 wrote: I did not have the bass distortion problem before the amp went out and I recapped it, so I have to believe it is all associated with either the amp failure, a component replacement, or a tube. Can anyone point me in the right direction, as to what to check next? Thanks for the help in advance.
Julian

You forgot one thing...
YOU were in the unit...

I think it's a case of mis-wiring or a shorted connection.

Julian,
My GUESS would be, in a situation like this--"human error". I suspect that you removed some component from a terminal strip, and installed the new component onto an adjoining terminal, in error. It is also possible that one of the new components is bad, or that a component is not the correct one ( even if you purchased a kit, (with the "C" numbers marked). I would attempt to trouble shoot this by checking DC voltages.--Be sure to run a 60 watt incandescent lamp in series with the line voltage while "testing"-- Good luck !
BTW--The MRA-5 amp does not belong in a "J"--it should have a HMFA-1J ( not a HMFA-1, either) amp installed. Ron Rich

A question for "handyman" -what pickup are you using. Some of those retrofit carts that used kiddie phono pickups (varco Ronnette etc) caused the sort of overload you are complaining about.

What may have occurred here is that before rebuild the existing interstage caps may have lost significant capacity thus reducing bass and making an overloaded front end less noticeable. All of the old Seeburgs that have not been rebuilt with have lower bass output do to this as well as lower gain which results in a higher volume control setting and thus less bass boost.

Front end overload will also cause AGC to lose control when the grid voltages exceeds the cathode. This will cause a lot of phasey and very bassy distortion.

Rob/NYC

Thanks to everyone for the quick responses. It certainly is not out of the question I made a mistake when recapping. I have recapped many radios, so I am very familiar with the task, but I also realize it is easy to make a mistake. I will try to verify all connections with the schematic and retest the resistors at that time as well. Rob, as to your question about the cartridge type, it is the red Seeburg Hi Fi pickup.

Ok, handyman, since you are using a redhead, do you have the original straight spike needles in it. These do have a lot more output than the bent styli. When I rebuilt my first V in 1985 the straight type were commonly available and that is what I used. They caused the AGC to overload and runaway on really hot records.

If the bass control truly has no effect that indicates an area to examine. This amp still used a loomed choke arrangement and dual pots. You have essentially two volume controls, one for bass and the other for mid-high. Check the values and connections around this section. Do you have a schematic? If not: http://www.verntisdale.com/schem/mra5-l6.jpg

Let us know what you find.

Rob

Rob,
I guess I will have to display my ignorance here. I am not sure how to tell the difference in the 2 type needles you asked me about. The ones in my cartridge slide into the redhead cartridge on a very light blue insert. They come out of the insert and then turn at a 90 degree angle for a 1/16' or so and then the needle is mounted at that point. There are several like them shown on ebay at this time. Hope that helps as a description.

I will check all components around the areas you describe. You are correct - the bass control makes no difference at all on the sound of the bass. The only thing that makes any change is to turn the volume control way down, but you can still tell it is over powered as compared to the treble. The treble control makes no difference either, as far as the over powered bass is concerned.

Ron Rich, I did check again on the tag on the amp. It is stamped MRA5-L6. There is no J on the tag, so perhaps the amp has been changed at some time in the past. It is the one shown at the link that Bob provided. I have printed that schematic out and will check the voltages at the various points shown on it, particularly the areas Bob has suggested. It is also the same one that is in my manual for the R. I had rebuilt an R a couple of years ago and had the manual for it. In fact, I worked with you quite a bit on it, including getting and using your mech guide. This J has been in my rec room for years and never gave a problem until now. I had just gotten lazy and never recapped the amp until it failed. Now I can't seem to get the bass right, but with the guidance from this site, I will keep trying. BTW, why the 60 watt bulb in series while testing? I am certainly going to use one as you suggest, just curious what it is for.

Thanks again for everyone's help.

Julian

Hi Julian,
You have the later, aftermarket, "stereo compatible" type needles. Originals have no "bend" in them.
Whatever chart is posted is incorrect--
The lamp, in the "117vac" circuit is used a "ballast", and / or "current limiting" --if there is a short. the lamp will light up-full brilliance, and usually, save the transformer(s). If there are no shorts, the lamp should lite at about half-brilliance for a second or two, then go dim, or out, totally.
Ron Rich

Ron's suggestion of a 60 watt "safety lamp" is only good for preventing serious damage to the amp in cases something shorts out.
But if voltages need checking in the amp, a safety tester absorbs some of the current/voltage and actual amp voltages will be substantially low due to this.
So comparing voltages to the schematic will be way off.

Ron Rich,

First my apologizes for providing incorrect information on my amp question and not paying close enough attention when I answered you back. I had stated I had a MRA5-L6 in my Seeburg J. That is the one that was in my R and I had read somewhere the same amp was used in the J. When I looked at the tag on my amp, I was expecting it to be the same one, so I was just paying attention to the L6 ending, not the complete number -stupid on my part I agree. Anyway, when you mentioned it should not have the MRA5-L6, again I just glanced at the tag looking for a J and verifying the L6 part. That said, after starting to verify my wiring with the MRA5-L6 schematic, it quickly became apparent something was wrong. I reverified the amp tag and realized it is an HFMA1-L6. At least I got the L6 part right. Anyway, again sorry for the incorrect information.

I have been verifying the wiring and so far everything is exactly by the schematic for the HFMA1-L6, as it should be. I have a ways to go, but thought it might be easier to just verify voltages, according to the schematic. My question is concerning providing voltage to the various stages of the amp, while still in the cabinet, without selecting records. If I try to verify the voltage readings without a selection made, there is no voltage present at the locations I am trying to verify. Is there a way to power the stages of the amp, while in the cabinet, without making a selection. I know there is some notes on the bottom of the schematic I have, but they are not really legible. It looks like it says the voltages are taken with pin 3 of J4 grounded and then pin 3 is read ungrounded, or perhaps with pin 1 not grounded. It is just not legible enough to read. Would grounding pin 3 of J4 power the amp stages without making a selection?

I am sure this is a dumb question, but had to ask. Also, given the issue I have with this amp, which voltage points would you think to be most suspect to verify first? As always, any guidance would be appreciated.

Julian

Hi Julian,
Well, if you have a HMFA-1, L6, You're closer, but, you still do not have the "correct amp" for a J-JL model phono. You should have a HMFA-1 L6J model amp.
If your schematic is unreadable, I suggest you purchase a "J" service manual, from one of the "legit" sellers listed above, in this section, of the forum, as it should have the correct schematic, in very readable form.
The reason you can not check voltages without making a selection, is that the 5U4 rectifier tube is not energized unless a selection has been made. This also energizes the mechanism motor at the same time. What you may be able to do, is remove the motor plug from the WSR. to accomplish your goal--
Ron Rich

Handyman, personally, I don't think voltage readings are going to get you anywhere.

Since we are talking about an HFMA1-l6 -that is an amp for a V-VL. I have three in service and the principal difference is the use of lower value coupling caps to reduce bass response in "J". Where the V-VL version has 0.47 caps, the J will have 0.02. This will not be the cause of your problem though.

The bass and treble controls act on different stages of the amp. The treble control is between the two stages of the 6SN7 and simply adds capacitance across the audio path as treble is reduced.

The bass control is integrated with the volume control taps. As the positions go down in number more resistance is added to reduce the effect of the taps and their capacitors. Connect your tester from chassis ground to each loudness tap on the volume control (there are the two tabs separate from the three at the other end) Set the volume control to maximum, connect the meter to one loudness tab, set meter to some ohms range well over 20k/ohm and adjust the bass control. You should see a wide range of readings with lower resistance occurring as the bass control is lowered.

While we are there, check the connection of the capacitor that comes from Pin 3 of 6SN7 to Pin 1 of the volume control plug. This must connect to the -high- side of the volume pot -not- the arm. Check also that the volume control is somewhere near 25k-ohm. I've seen all sorts of pots used as subs in these along with improper wiring.

Rob/NYC

Thanks, I will do that and report back what I find.

Rob,

I have verified the readings in your message. First, the connection and size of the cap on pin 3 of the 6SN7. Electrically, it is connected to the high side of the volume control. Physically, it goes from pin 3 to a wiring terminal to the side and below the tube. From the lug on the wiring terminal, it goes to pin 1 of the J1(Remote Volume Control) plug. Pin 1 is connected to Pin 2 internally in the plug. Pin 2 is wired directly back to the high side of the volume control. I have verified all connections are good and there is continuity in the circuit from the cap through the J1 to the volume control. The cap in this circuit is a new 1UF cap. As far as I can tell, both the cap and the circuit are correct according to the schematic.

I also verified the connections and the resistance in the volume control. With all wires off of the control, it measures 29K ohms. Using the center tab, the resistance goes from 0 - 29K. Measuring from the low side terminal to the 2 tabs on the opposite side of the volume control with all wires off, I see the following measurements - one tab reads 18K and the other reads 85K, neither change in value when the volume control is turned.

Now, with all wires back on their respective terminals, I read the following measurements. The overall resistance of the volume control reads 16.8K. Using the center terminal again, with all wires on, the volume control measures from .11K on the low side to 16.8K on the high side.

Putting one lead of the VOM to chassis ground and measuring to the two tabs on the opposite end as you instructed, I get the following - 1st terminal - 24.6K with bass on high down to 1.2K with bass all the way on low. 2nd terminal - 22.0K with bass on high, down to 1.2K with bass on low. When I first connect to the terminal there is quite a bit of flucuation in the meter, but then it settles down to the measurements above. The high measurement does change considerably, depending on where I access the equipment ground. I am not sure if that is normal or not. The measurements shown are with a chassis ground close to the bass control.

Again, thanks for the help.

Ok, the connections from the tube to the volume control seem right.


"18K and the other reads 85K" I'll have to dig out a new control, but from memory, the tap closest to the ground terminal should be around 7-8K and the second higher one 17K. 85K is way off. However having the taps go higher would -lessen- the bass boost and just result in using a lower volume control setting.

The good news is that the bass control itself is operating correctly, The bad news is that the off values of the volume control are why it has little/no effect. To restore bass control you will need a new volume pot, I've bought 7 repro's from Vern Tisdale to make RVC's in my locations and they are accurate.

The varying ground reading is odd since the internal volume pot should be directly connected to chassis ground and not dependent on the often troublesome RVC jumper pins.

You've done a good job of troubleshooting this area, I'll have to think about what else might be causing the excessive bass.

Rob