Flourescent lighting for Dummies

I'm almost embarrassed to even ask, but I know nothing about flourescent lighting.

I was tracking down a "hum" on my Rowe R-90 (1986) and recalled reading here that the lights can cause this. I disconnected the plug to the lighting and my hum stopped right away. The box is quiet as a mouse when not playing and all lit up - this hum only occurs when a record is playing.
I have determined that it's one of the lights on the door causing this. I can power the cabinet lamp up and no hum. As soon as I plug in the door lamps, it comes right back.

It seems like the ballast would the responsible part, but the posts here point to a constant hum any time the lights are on and that isn't my problem. Could the ballast still be the culprit? Or perhaps the hum with the lighting is just a symptom and not the cause?

If it is the ballast, then that leads to another round of questions for me. It seems that there are several types and I have no clue what the difference is or what I need to replace. Manual only gives me Rowe part numbers - little use at Home Depot.

Any help is, as always, much appreciated!

Thanks,
Nelson

Hi Nelson,
First thing to check in this type situation, is "grounding"--is the ballast, AND the "lamp fixture" grounded all the way back to the power cord (which MUST have the three wire plug on it) ? If so, try switching the two wires that are used on the ballast itself. You are picking up "induced hum" when that lamp is lit. You do not hear it between records as the amp is "muted". Also check that there are no "lamp cords" running parallel with the audio wires to the speakers.
What is the size/type of the lamp you are using ?
Ron Rich

Thanks Ron -
I verified that everything has a (secure) ground, I am using a 3 prong plug to the house and I made sure the polarity is correct at the outlet. The AC gets to the door via an AMP plug - made sure all those connections were good and tight. I took a piece of 12ga wire, put ends on it and ran it right from a ground on the amp to a ground screw on the door. None of that has made a difference.

The woofers are in the cabinet, but the mids are on the door. The factory has all those wires running together, so I would guess that's ok.
I'm not getting any hum if I pull the input to the amp so it doesn't appear to be back feeding through the speaker wires. The hum gets MUCH worse if I go near the tonearm or touch it. I'd think I have a flaky cartridge, but it sounds perfectly fine without the door lights lit. Just for giggles, I moved my homemade ground wire and screwed it to the mech ground, no change.

When you say "switch" the ballast wires, this is the black and white I should swap? Haven't tried that yet.

It has 2 lights in the door. The horizontal lamp is a F30T8 and the vertical is a F26T8

Thanks!
Nelson

Hi Nelson,
I did not know there were two lamps in the door--pull them one at a time to see if that makes any difference ?
I;m confused as to why touching the tone arm makes it hum--but only when the lamps are plugged in ??--do they use the same plug for audio and lamp power ?
Ron Rich

Nice to have some company in my confusion

I disconnected the ballast for one then the other, but the hum remained with each one on. The only way to get rid of it is to kill both lights. The amp and the lights do plug into the main power supply, but separately. The amp is a standard 3 prong plug and the receptacle is mounted in the power supply cabinet and is just an extension of the wall plug really. The lights are on a 3 conductor amp plug. The upper cabinet light causes no problem, just the 2 in the door, even though they all originate from the same main plug.

Yes, the tonearm part is confusing to me. The hum seems like it gets amplified by the cartridge. I can increase the volume by moving my hand closer to it and it gets much louder if I actually touch it. The highest volume comes from touching the cartridge itself, not the needle. The tonearm is acting very much like the loop antenna on a theremin. If I unplug the door lights everything is perfect, even if I touch the cartridge. I did try grounding myself to the amp when I touch the tonearm, no change.

The exact same type ballast is on the upper cabinet lamp, so maybe I can swap them and see if it makes any difference. I don't have a spare cartridge, but I can pull the one from my Rockola and try it to see if anything changes. I'm just not sure if I have something that needs replacing or if I'm chasing some sort of gremlin in the system that new parts won't fix. All part of the fun I suppose

Thanks!
Nelson

Nelson, there should not be a hum when you touch either the cart or the arm. That indicates that someone has mis-wired or replaced the cart.

Take a look at these pic's

http://s1192.photobucket.com/user/Rob-N ... sort=3&o=0

http://s1192.photobucket.com/user/Rob-N ... sort=3&o=1

These are the typical Rowe/Shure M44 used till the end of vinyl production around 1993.

The cart is a plastic body around a metal shield.

Note that the bottom terminal on the rear of the cart grounds the inner metal shield. This must be connected to a shield on the tonearm cable. If it is connected to a 'hot lead the entire cart body becomes sensitive to external fields. That is what is happening in your case.

It is also necessary that the bolt heads do not touch the inner shield as this creates a ground loop and will cause a constant low-lever hum.

So, get your schematic and continuity meter, trace out the proper wiring and the hum should be done.

I had three of the R91 and R92 machines on location in the late 80-early 90's. Far-and-away the best sounding machines, a real pleasure to listen to without the need for mods. In fact the combo Cd/record was much better sounding than the all-Cd machines at that time. I did NOT like the tonearms though.

Rob/NYC

Rob,

Great call! I did as you said and got out the meter - no continuity from the cart ground to the amp ground. Tracing backwards, I discovered that 2 of the wires were swapped around in the plug going to the mech connection. I put everything back where they belong and **POOF** no hum!

The previous owner had put a new cartridge on it, but he was a bit clueless. He had actually installed it backwards and also jacked up all the tonearm adjustments. I suppose I should have triple checked every little thing in the areas he was working in. On the positive side, his lack of success prevented him from doing any more "repairs" and I picked it up for $100, full of 45s!

I appreciate the input from everyone - got me all fixed up and I learned something new!

Thanks!
Nelson