fred
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Posts: 8 
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Post by fred on Oct 11, 2017 18:58:47 GMT
I am working on a Seeburg Library unit LU-3 The mechanism has been completely cleaned, oiled and adjusted. All the switches have been cleaned and adjusted. The selector panel has been rebuilt. The blackhead cartridge ohm's at .08 and it has new .7 needles. All in all it was running great and sounded good. However after playing it for a few hours on the bench I started getting a screeching sound on the highs of the music When the symbol was struck or the treble was needed. Even a high pitched voice you could hear it. I turned the treble down and some of it went away but you can still hear it. It's getting worse as I play it. The Preamp was Re-capped last year however when i took the cover off there were new and old caps. I took it to a guy I know. He replaced the old caps that were left and checked over everything but it still makes what I call a screeching when a cymbal crash. I went out on the Internet for some clues, I found a web site for old style guitar amps. They made a good case that one or more of the drive tubes was going bad. I have tested the tubes with one exception there is no references for this tube RCA 5879 Again I went out on the net and found back in the day this was an exclusive tube and there were no replacement or alternatives. The tubes went as follows with the reading in ( ) 6BJ6 (82) 12BH7 (79) 6C4 (85) 12AX7 (80) 6x4 (60) RCA 5879 ?? While I was looking for answers I decided to replace the 6 X 4 and the 5879. Still the problem persists I am leaning towards the cartridge now If I put a little more pressure on the tone arm spring it seems to go away, However I don't want to destroy my records
I took the worst record and recorded it but the file is over the limit for the site I could pass it on if anyone wants to listen to it. It's 30 sec 3.3 megs
Anyone who wants to give an opinion or clue where to look thank you in advance for your help.
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Post by Ron Rich on Oct 11, 2017 19:34:51 GMT
Hi Fred,
Something like that, even if I could hear it is difficult-- My guess would be a resistor changing value in/around the 5879--not a hard tube to locate --check the FAQ's above for various sellers--If it's the tube itself--no "tube tester" will show that type problem. I would first change that tube----does this only happen after a long play time--? If so, might try spraying some "freeze spray" on the components near that tube--if possible-- Needle pressure is CRITICAL on the new replacement "stereo" black and red head stylii-- Set the black heads at 7 grams--redheads at 4 grams, MAX, in both cases !! Ron Rich
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Post by robnyc on Oct 11, 2017 20:51:57 GMT
That is a typical example of disintegrated damping pads in the pickup. These are tiny rubber pads that absorb the chatter (resonance) of the stylus cantilever.
If you are skillful, you can fabricate and install new pads. Otherwise, send it out.
RobNYC
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fred
New Member
Posts: 8
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Post by fred on Oct 11, 2017 21:15:45 GMT
Hello Rob
Can you expand the information on these pads
Maybe a picture as it is looking at the cartridge there is small piece of metal sticking out that the needle slips into. Now it moves left and right freely are you saying there needs to be a padding around it to absorb shock or vibrations
Thanks
Fred
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Post by Ron Rich on Oct 11, 2017 21:16:10 GMT
Hi Rob,
I question your diagnosis here-- Why would this be the case after a "few hours" playing--can and do understand this happens with this type cart--but my assumption would be that time would be no factor ? Ron Rich
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Post by robnyc on Oct 11, 2017 21:27:50 GMT
"Hi Rob,
I question your diagnosis here-- Why would this be the case after a "few hours" playing--"
Ron, the old rubber has sat in one position for decades -not moved. Once the stresses of of vibration and the tracking force act upon it the brittle rubber begins to crumble.
I have a couple of the old relics. Both were playable when I got them from an op back in 1986. Both would need rebuilding if I had any interest in using them today. That extra 31 years makes a big difference.
Rob
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Post by robnyc on Oct 11, 2017 21:30:39 GMT
Fred, the pads are inside -snugly around the protruding shaft that the stylus fits into.
If you have any sort of amp/receiver with magnetic input you can plug the mech pickup into that and confirm for yourself where the distortion is coming from.
Rob
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Post by Ron Rich on Oct 11, 2017 21:37:07 GMT
Hi Rob,
Yep--but, I just do not understand why it will play for a few hours--" If it sounds OK after it cools off, I doubt the rubber,is causing this problem--You are reading what Fred wrote as being bad,at all times, now--I assumed it only happened after playing, each time, after a few hours ?-- Hopefully he will soon chime in, and answer that question--- Ron Rich
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fred
New Member
Posts: 8
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Post by fred on Oct 12, 2017 1:00:22 GMT
Hello
I think Rob is onto something I just got home. As I said it was getting worse and worse now I turned the unit on and the noise started right off there was no warm up needed It's like the rubber was falling apart little by little until now I pulled the cartridge, looking under a ten power scope what I thought do be dust and vinyl residue are flakes of rubber like neoprene
Can I replace this? How far does this rubber go inside. Can there be to much packing. I have a bunch of neoprene rubber stick on pads. there about 3/16 thick do you think I could cut the shape of the hole in the cartridge then a slot and slide it over the metal for the needle and tuck it inside most people would say it's done but is it? I have to know for sure
Thanks
Fred
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Post by Ron Rich on Oct 12, 2017 2:56:07 GMT
Fred,
If that's the case, it's really not too hard to do--grinding off the rivet, and finding a small screw/nut to replace it is the hardest--I had a friend who I watched do several of them -- He liked to use the thick rubber bands the newspapers were bound with -- This still can be an electronic problem--noway to tell unless you sub some things out--Ron Rich
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Post by robnyc on Oct 12, 2017 7:09:06 GMT
Fred, have a look at the insides of a black head: www.flickr.com/photos/90641375@N06/37649693321/in/dateposted-public/ On this shot you can see that the cart has been previously 'repaired" using a slice of rubber band. The rubber band was hard a rock so after touching it disintegrated. Here is the innards au natural: www.flickr.com/photos/90641375@N06/37649683281/in/dateposted-public/This was one of the carts given to me in 1986 to 'play around with" after buying the first V and being dissatisfied with red pickup. One op I knew gave me several more redheads saying that 'some tend to sound different". -this is true. The blackhead has a much lower impedance and seemed to sound relatively better. All of these are primitive, but in this case it makes them easily repairable. None of these were considered worth anything at that time. Many were thrown into drawers and boxes -most were just thrown out. I rescued a stereo redhead from the dirt floor of a garage one op was clearing out in Jersey City in 1989. So do as Ron suggests, carefully drill open the cart and cut a piece of rubber band, poke a tiny hole in it to allow the stylus chuck to fit through and close it up with small nut & bolt. While at it, check that the little centering wire that is soldered to the stator has not broken off --they do sometimes. RobNYC |
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Post by Ron Rich on Oct 12, 2017 12:52:43 GMT
Rob, This forum has some (not many) "rules", and you have just violated one ! NUDE photo's are prohibited ! Do not do this again, or we will call the geppetos to tie you to the nearest telephone pole and whip you with wet noodles !  Fred, If you do open this unit--be sure the nut you use to keep it closed is thin enough not to scratch your records ! Ron Rich |
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fred
New Member
Posts: 8
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Post by fred on Oct 12, 2017 16:26:20 GMT
This is awesome I have always wanted a good excuse to open one of these up. I didn't have much time last night But I did take the red head from the B in the den and put it on the library unit it sounded 100% better If i was going to leave it I would have to adjust the springs a tiny bit. Other than that it sounded great. I love taking things apart to see how they work and trying to make them work again Seeing how I have the excuse I can't make it any worse is a plus in my book. Thanks for the pictures and the information I will post what happens for future reference
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Post by Ron Rich on Oct 12, 2017 19:10:48 GMT
Fred,
One thought comes to mind--there is an "arrow" on that casing--be sure you re-install that case with that arrow pointing in the correct direction--needle shank MUST also point in the direction of the arrow ! I have seen needles installed upside down--that don't work ! Ron Rich
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fred
New Member
Posts: 8
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Post by fred on Oct 13, 2017 16:56:57 GMT
Hello Well this is what I found. plus some questions First does the grease need to be replaced? if so is it non conductive? Second I did a lot of reading last night, Found a guy who rebuilds these. In his rebuilds he uses bicycle inner tube which I have. Do you think that is to thick or heavy? Does the rubber go under the tab or just on top (see arrow in photo) and on the last note from Ron I see the up arrow is on the dimpled side of the cartridge however the slots that the metal comes thru are at different heights they have to go on the correct side otherwise you will have to force and or brake it to make it fit Thank you for your input   |
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