Help Saving 400-CX SA-100 and 100-R Tuner

Discussion in 'Fisher' started by moondogtn, Oct 10, 2017.

  1. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    427
    Location:
    Pleasanton, TX
    Dave....It was the jumpers. I seriously was wondering about the plug but figured no one used the remote back then so it wouldn't be a requirement. I forgot to revisit that thought. Everything at this point seems to be working properly. Now, I will work on resistor value and keep you all posted.
    Thank you.

    Bill
     
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  2. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    Bill; On the Space Expander "U" shaped jumpers. Don't push them in all the way as they'll short to the outer connection and give you no sound/low sound. A piece of Heatshrink tubing, long enough to cover the "U" part and leaving the legs open will alleviate this problem. The pic shows the jumpers with heatshrink. This is on a 400 receiver. The 400cx jumpers are in different place but work the same.

    400 receiver space expander protection. 400 cx is in different location but work the same.
    400 space expander jumpers modded.JPG
     
  3. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

    Messages:
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    Larry -- Bill's CX is an early version that did not include the SpaceXpander jacks. Those did not appear until the CX2 version started being produced, but it always a good reminder to those with units that have those jacks.

    Dave
     
  4. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    427
    Location:
    Pleasanton, TX
    Guys, it was a busy day so no real progress here. I did manage to round up a handful of 5w resistors to parallel and create a 500 ohm jumper to give us a starting point. Once determined, I will order a suitable replacement for install. I’ll hopefully get to work on this tomorrow and report findings.

    Btw, I will need to add heatshrink to the jumpers 400 receiver. That is on the project list at some point....trying to finish this first.

    Bill
     
  5. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    427
    Location:
    Pleasanton, TX
    I just want to clarify the plan and the reasoning for adding the resistors as a friend asked me. I told him what I thought but didn’t want to misinform him.

    I added a pic of each area for illustration.
    1. The resistor (value yet to be determined) I will add from pin 3 on rectifier tube to the C45A will basically replace this jumper and will only drop the voltage going to this section? This is done because the components(C45A) aren’t rated for voltage currently being applied?

    2. This 1ohm resistor added here between the green wire and ground tab will reduce the voltage by decreasing the potential between the two windings?

    I’m just trying to further understand as well as ensure I install the resistor in the correct spot in the circuits.
    Thanks for your patience and guidance.

    Bill
     

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  6. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

    Messages:
    9,300
    Location:
    Ball Ground, GA
    In the first pic (green circle), the lead of the 1.8K resistor attached to the rectifier tube socket should be moved over to the filter cap terminal on the other end of the jumper. Then replace the jumper with the new resistor to be determined. Adding this resistor reduces the B+ voltages down to the specified voltage at C45A. By dropping the voltage to this first filter cap section, all the rest of the B+ voltages will then fall in line appropriately.

    The installation of the 1Ω resistor is correct as described. However, I forgot about the heater of V4 also operating from the AC heater winding, so it should actually be a .5Ω 2 watt resistor (two 1Ω resistors in parallel). By adding this resistance into the circuit, the voltage to the AC powered heaters and the indicator lamps will then be very nearly 6.3 vac, rather than the 7 volts you indicated they were receiving.

    The voltage level to the tube heaters powered by DC is correct, so lowering the B+ and AC heater voltage by adjusting the voltage to the primary winding of the transformer would then leave the voltage to the DC powered heaters too low. Therefore, the B+ and AC powered heater voltages are each adjusted individually, allowing the B+, AC heater voltage, and DC heater voltage to be correct.

    I hope that helps!

    Dave
     
  7. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    427
    Location:
    Pleasanton, TX
    Dave, yes, that clears things up immensely! Thank you for taking the time to explain.

    We were successful on bringing the 7 volts down to 6.5. I used a 5 watt .47 ohm resistor I had on hand. If I really should go with a 2 watt, I can order one. If not, I’ll leave that one be.

    The other voltage doesn’t seem to want to cooperate as easily.
    Black lead to ground and positive on C45A tab,
    437 VDC @ 250ohms
    420 VDC @ 500
    414 VDC @ 600
    I had to quit as I am out of resistors.
    I only had 10 watt resistors so I hooked them up in series to get these values. I will need to order some more for further testing.

    Just a thought, I have a milliamp clamp that may help us determine resistance required by giving us the current being used?

    Bill
     
  8. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

    Messages:
    9,300
    Location:
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    Not really. There is DC as well as AC (ripple) current flowing through the resistor, which is why simple Ohms Law won't work. If you need to use as much as a 1K resistor or more, there is nothing wrong with that. Because all of the tubes operate in Class A, current draw from the power supply is constant regardless of function used or signal level through the unit. Whatever value you need is whatever value you need.

    Dave
     
  9. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    427
    Location:
    Pleasanton, TX
    Resistors should be here tomorrow according to tracking info. I’m hoping I can get voltage dialed in and report back.

    In the meantime, another silly question is how do I remove these bulbs? I think they are just bayonet type 47 bulbs and I have replacements but don’t want to damage anything removing the old ones. They are installed with a black rubber hose looking surrounding them and has shrunk and hardened( I think) This make them difficult to access. I assume it may be asbestos lined to isolate heat/light transmission?

    Edit, I got it. Just a little slow coaxing and the tube will come off...then, swap the bulb.

    Bill
     
    Last edited: Apr 9, 2018

     

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  10. AlTinkster92

    AlTinkster92 AK Subscriber Subscriber

    Messages:
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    Moon, yeah those tubes are on several Fisher pieces, my X202B included. What I did to replace a bulb was after I couldn't get the tube off I pushed in the rubber tube and rotated the whole thing to get the bulb out. You might also try a pair of needle nose on the tube and be able to pull it off that way. Good luck with it!
     
  11. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    427
    Location:
    Pleasanton, TX
    AI, that’s what I used to get them off. It would have been easier to remove all the black tubing, then remove the two screws holding lamp assembly so that it could move. I noticed that after I was halfway done.

    Resistors arrived... it looks like 1.2 or 1.3 kohms will do the trick. I had
    387 VDC @ 1.3kohms
    393 VDC @ 1.2kohms
    So, now I will just need to order proper size 5W resistor and install it permanently.
    Actually, that 1kohm 5w is pretty warm to touch. Should I up it to a 10W? Same with the 1.8Kohm resistor. Both are fairly warm.
    Edit: 12ohm 7w really gets hot? Should it be upped too?
    Thoughts?
    Slowly but surely, good thing I am not I a hurry.
    Thanks

    Bill
     
  12. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    12ohm 7W up to 10W. the 1Kohm 5W you can bump to a 7W or 10W. Same with the 1.8K (provided it's 5W, bump to 7W or 10W) otherwise bump to next common wattage.
     
  13. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    427
    Location:
    Pleasanton, TX
    Thank you, Larry. Since I will be buying new resistors, are there any specific or recommended types?
    I filtered these results for the 12 Ohm upped to 10 watt rating. I was thinking of this...

    http://www.newark.com/ohmite/20j12re/wirewound-resistor-12-ohm-10w/dp/64K7969
    or
    https://www.mouser.com/ProductDetail/Ohmite/20J12RE?qs=sGAEpiMZZMtlubZbdhIBIB1Nwu1NRkE1rNIkl0lOXkA=
    or
    https://www.mouser.com/ProductDetai...=sGAEpiMZZMtlubZbdhIBIGo76SrG4wpqNO34/EY4E58=


    Filtered results

    http://www.newark.com/c/passive-components/resistors-fixed-value?resistance=12ohm&power-rating=10w

    https://www.mouser.com/Passive-Components/Resistors/_/N-5g9n?P=1z0x714Z1z0wt4w

    I am probably overcomplicating this but figure I may as well get the correct resistor for the application. Thanks again for any insight here on selection.

    Bill
     
  14. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
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    Location:
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    I tend to Ohmite's as 1st choice and Vishay's 2nd. And I pretty much use Mouser exclusively. Both are good choices and will work fine.
     
  15. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    427
    Location:
    Pleasanton, TX
    I ended getting ohmite 10 watt and installed for the 1200 ohm. Nice and cool and sounds incredibly sweet. Only thing is my voltage is 382? I checked my previous setup and I had 1.2k?
    I think it’ll suffice. What do y’all say?
    Others I left alone as I feel they weren’t too hot just hotter than what I had anticipated.
    I’d like to button it up so I can listen to it with some real speakers in my other room.
    I’ll post some pics shortly.

    Bill
     
  16. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

    Messages:
    9,300
    Location:
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    Bill -- That's plenty close enough, and well within the normal limits of variation allowed. It will do just fine!

    Dave
     

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