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X101B, Hi-FREQ(10KHz) Phono Squeal, Volume Dependent

Discussion in 'Fisher' started by larryderouin, Sep 10, 2016.

  1. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

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    I finally got the 101-B set up in the Living room with the KM-60. All is fine in all functions with NO ADDITIONAL SOURCES CONNECTED. In PHONO ONLY, when I connect a T.T. (and I connected 3 different ones), I get a High Frequency hum/squeal that is volume dependent. Doesn't matter if it's connected to MAG 1, MAG2, or CERAMIC, The Noise is there. Frequency is about 10K by estimate. Turntables can be grounded or non grounded No difference. Changing Cartridges makes no difference.

    Before I got the squeal, I had an intermittent in the V6 socket where the .02uf cap was grounding out due to the way it was sitting causing a 3-4db drop in volume on the RIGHT SIDE ONLY. Wiggling the tube could open the ground. So I got inside, found the problem and reset the position of the cap and retested to see if I had volume on the Right side.

    Right side volume is now equal of the left, but the high frequency squeal, hum,hiss replaced it, and on BOTH CHANNELS. IT's totally dependent on volume level, can be reduced by applying the High Filter, and by turning the Treble all the way down. It doesn't go away until I disconnect the turntable from the amp.

    The Phono section on the 101b has not been recapped, and voltages on V6 and V1 are within 1% of schematic voltages on all pins.

    I'm gonna replace the .01 and /02 ceramic caps in the phono section with Films this weekend. and which ever ceramics that hadn't been replaced yet. I did notice that the Tube Sockets for phono tubes are hard riveted to the chassis

    I'm debating on whether it would be a good idea to drill out the rivets and install rubber grommets (as in the receivers) and the attendant screws and nuts,then run a ground wire from the sockets to a ground point on the chassis between the tubes? Or is it a BAD IDEA?
     
    Last edited: Sep 10, 2016
  2. arts

    arts Super Member

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    I've also had preamp tubes that gave the same effect,possibly due to inter-element leakage or bad internal connections.Bad sockets do it too.

    I really think the rubber grommet ''isolation'' method was a pretty lousy idea with a really minimal performance benefit.You need to wire to the socket with super-flexible Litz leads.And unless you are able to source VERY compliant rubber grommets,I doubt it would be worth the amount of time and effort involved.That and the thought of drilling or grinding out those rivets in a crowded chassis gives me the shudders!
     
  3. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

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    I changed the caps (.01 and .02 ceramics) for yellow Axials same value and 400v. The noise is still there but diminished about 1/2. I did notice when trying to wiggle the RCA's that it would cut in and out, so the RCA's are next on the list. I get some Radio interference on the PHONO that is not connected to a source. But when a TT connected to that source, the radio interference stops and the squel starts. Lousy ground? Loose center connection?. I'll get back in there and tighten up and re-solder the center connections and ensure the grounds are tight and clean, with fresh solder. I may have to fabricate a board for new RCA plugs too......not that I want to. The Phono sockets DO wiggle in their mounts a lot more than the rest fo them. So that may have something to do with it.


    I agree with drilling the rivets out is a PITA in a crowded socket. Being as they are loose in the mounts I think drilling them out, flattening out the mounting ring, and installing the ring with a screw and nut will probably benefit the sockets, and the sound. I've got the correct size rubber grommets for the Phono sections that use them. As long as you don't squeeze them flat they DO isolate quite well. Most guys tighten the hell out of them(As did FISHER) and then they just look like they are working but in actually they are maintaining or in some cases increasing the vibrations going thru them. Turn them in and watch the grommet for deformation. Stop tightening as soon as it starts to deform. Just like you do on shocks that come with the rubber isolators.
     
  4. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    If you put in some shorting plugs into the selected phono input, does it go away?

    Dave
     
  5. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

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    Yes for the shorting plugs with regards to the FM bleedover. Low level has to be maxed out, and Main volume has to be approx 3pm to hear it clearly. IT comes on about 12:00. But the Shorting plugs definately kill the interference.

    The HIGH SQUEAL only occurs with a turntable connected. And the level of squeal is slightly different with each one.
     
  6. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    One thing you might check: Fisher was bad about having magnetic inputs located very near the output tubes, which is a recipe for HF oscillation when the gain is elevated and the input is not shorted. In many models, they installed little shield plates to prevent such oscillation. You might check if yours is missing one, or, you may need to fabricate one. I've had to do this on a number of occasions on units where I've flattened out the HF response from a previously rolled off stock design.

    Dave
     
  7. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

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    Ok. I'll see what I can find around the house btwn now and monday morning. It'll be a couple months before I can work on it, unelss I put it on the bench right now. Surgery is scheduled for Monday at 0900. Gotta get up @ 0500 to make a 0700 intake.

    Just remembered. I put in 10 ohm cathode resistors y'day. NO Shields. I've got an old 700-T junk chassis out in the shed. It's got a hell of a center shield plate. Cut some off and fashion a plate for the X-101-B and solder it in to the chassis.
     
  8. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

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    This what you're talking about, Dave? I figured just the phono stages, as the line level inputs are dead quiet. Just like I thought. The 700-T scrap chassis "had" a shield right down the middle. Removed all the cable shielding, rivets, etc. Then lined up both sides and cut with a dremel. Cut a groove in the middle to make the bend, which lined right up between the RCA Mounts. Then cut it down to depth with the dremel. Took all of 15 minutes. Soldering was almost as much time, but they are secure and read 0.0ohms. The cables come down a couple metal cable shields down the side so had to notch around them. Now to test it all in the morning. Last day of relative free movement before the surgery.
    100_5088.JPG


    100_5086.JPG

    100_5085.JPG
     
    Last edited: Sep 10, 2016
  9. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    Super Duper Job, Larry! That's exactly what I'm talking about. You see how close those magnetic input jacks are to the output tube sockets. Even if this is not your problem, you've really eliminated a potential problem and greatly enhanced the build. Let us know, and good luck with the surgery!!

    Dave
     
  10. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

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    Dave split the "X" in the X-ring on the target with this one. Changing the caps didn't alleviate the squeal or the FM bleed over (I didn't expect them to really but they DID need replacing) But fabricating and installing that little bit of shielding improved the SQ immensely! .

    Fantastic response on the X-101-B. DEAD QUIET even with ear up to the speaker cones with the volume maxed, treble maxed, and low level maxed. Source in, Source out, Shorting plugs in, NO DIFFERENCE, It's a TOMB!!!

    HIGHLY RECOMMEND this UPDATE/MOD for any X-101-B owner or even ANY FISHER that has the PHONO (low level) inputs right up against the output tubes. And it's totally reversible, and nobody will notice it had been there at one time.
     
  11. arts

    arts Super Member

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    Good luck with the surgery Larry!

    Be well,

    Art
     
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  12. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

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    Thanks Art. Right now I'm a bundle of nerves. Wife is in Hospital for diverticulitis, so #2 son is driving me in tomorrow morning(Different Hospital). I won't go to the local hospital unless it's in the back of a Meat Wagon. SURGERY THERE? NO WAY! So I travel 20 miles to the Hospital in Annapolis.
    Better Doc's, more modern, and not affiliated with University of Md. Hospital. (I absolutely loathe UMMH)
    Here's what my guts feel like right now!

    knotted up guts.jpg
     
  13. RS Steve

    RS Steve Tube Junkie Subscriber

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    Hope all goes well tomorrow Larry, and congrats on solving the phono issue.
     
  14. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

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    DAMNED THING CAME BACK and NO RIGHT SIDE NOW in phono. I pulled the new Tung-Sols and put in a couple Tele's, thinking it may be a tube. NO JOY! So now I have to open it up and check the grounds and hots, and tighten up the connections on the RCA JACKS. Good Thing it don't take much for me to pack.
     
  15. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    And, it keeps you out of trouble and off the streets at night, too! :) These kinds of problems can be insidious to deal with, and it may end up being multiple things that add up to the total resolve. You'll find it, I have no doubt!

    Dave
     
  16. vendo81

    vendo81 AK Subscriber Subscriber

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    Nice job on the cables Larry.
    Best of luck with your surgery!
     
  17. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

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    I guess it'll haveto be worked on After I can hoist 30+ lbs.

    1)I soldered the cable shields to the plate shield directly at the corner where they pass into the corner. NO CHANGE in squeal.

    2.) Tightened the RCA Jacks. No Change.

    3.) Ohmed out the grounds. 0.0 to 0.1ohm on all of them.

    4.) Channel "A" (LEFT) is muddy with an attendent drop in Volume plus the squeal. No crossed wires, resistors, caps, etc in the circuit I can find. I did replace the .01 and .02 ceramics in the phono section with Yellow axials of same value and 400v. These were run as the ceramics'.

    5.) Channel "B" has the squeal and it's increased since last.

    6.) I did notice that Channel "A" would hum as I removed the (V1) tube shield. Hum would stop when shield completely disconnected. Hum would start again when I placed a finger on the tube envelope. Channel "B"(V6) Right stayed quiet except for squeal.

    7.On the TAPE/PHONO EQ Switch, I get a blast of sound when the switch is over center. Sounds like I need to install a new switch.

    OnTuner, AUX, RECORDER IN I get absolutely no squeal.
     
  18. Omegaman

    Omegaman Ultra Super Member Subscriber

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    Well, the surgery should be complete by now

    Let the healing begin

    Jeez, my wife is suffering with Diverticulitis as well but not in the hospital yet
     
  19. tnsmnichols

    tnsmnichols Member

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    Larry, best wishes to you and your wife.

    I hope you will soon be back on your feet, and soldering late into the night!
     
  20. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

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    back SURGERY SUCCESS! RESIDUAL PAIN IS A M..F.. dilaudid and morphine are a joke;altho valium does help some,
     
    Last edited: Sep 14, 2016
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