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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:
    485
    Location:
    Pleasanton, TX
    Dave, I have them set pretty close to what they were prior to cleaning and lubing them. I measured and also marked. I can make notes and go to mid point though if that is preferable. Thank you

    Bill
     

     

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  2. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    Tone Controls go to Center Point. Loudness OFF, Any and all volume controls on Front panel to minimum. Don't worry about any level controls on the back. Source Selector to AUX, and Mode Selector to STEREO.
     
  3. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    485
    Location:
    Pleasanton, TX
    Okay gentlemen, I powered up and bulb was dim and no smoke. So, I removed it and started. I just got done with some of the voltages. Btw, there is no aux selector? The stereo switch was set to stereo.
    I posted a pic of voltages noted on schematic but will list here for reference. If there is an easier way to write these, let me know.

    I was using a Variac set to 117 volts.

    First I checked transformer voltages.
    Yellow leads read 420 (5.1 vac between them. )
    Orange and yellow read 6.5vac between them.
    Then the two red, 365 vac each
    The red/Black I had 65 vac before r56, and 46 after it. I checked and it measured 2.2kohms. On negative side of diode, my dc voltage was -26.
    Then I checked the cap
    C1A 400
    C1B 306
    C1C 312
    C1D 305

    The negative voltages off of the bias resistors were
    C3 -15.5
    C4 -13
    I’m going to need to call it a night but wanted to post those initial findings to see if those look ok so far.
    Most notably off was the 65 vac, 46, but once rectified seems to be close -26?

    Bill
     

    Attached Files:

    Last edited: Jun 6, 2018
  4. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    You will want to adjust the Bias and DC Balance controls first and then retake your readings as that can change them notably.

    Dave
     
  5. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    485
    Location:
    Pleasanton, TX
    I have a dumb question. On the first page of the service manual, it has adjustment procedures. The AC bias is first and it tells you to have speakers connected. That part is done.
    Next is DC bias...
    Do you leave the 8 ohm speakers speakers connected for the DC bias adjustment? Hook up positive to 16 ohm and neg lead to grd?
    Seem like dumb questions but would rather ask now than after I screwed something up.
    Also, I am using a fluke DMM, not a VTVM.

    Bill
     
  6. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

    Messages:
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    Location:
    Ball Ground, GA
    Modern DVMs don't work well with the Fisher procedure, because it's hard to decipher a low point with wandering digits. On the other hand, an average responding analog needle is very good at indicating a null point.

    You want the speakers connected during all the adjustment procedures, but consider using headphones connected directly to the output of the amplifier to determine a minimum output when adjusting the balance DC Balance controls.

    Dave
     

     

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  7. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
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    Location:
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    Dave, I was attempting the headphone method using alligator clips on the headphone plug to the speaker terminals but may have an old cable I can modify to use. Channel B it was an audible difference when it got quiet. Channel A was a bit more difficult to find a quiet, happy spot.
    Also, I was double checking and found R51, 52, and 54 were out of spec as they should be 4700 ohms. R51 was 3000. I then noticed they were the darker type that you mentioned. I looked and didn't see any others. I placed an order and now I guess I need to be patient for those to arrive before continuing. I will also see about picking up an analog meter. I know it will be useful. Thanks again.

    Bill
     
  8. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    485
    Location:
    Pleasanton, TX
    So, I got the new resistors installed. The dim bulb dimmed. I removed the bulb and set the AC to .6 for both channels. I set the DC balance using headphones. I was checked the variac and set for 115VAC. Then I began by checking the voltages that were off. I was still getting 43 volts upstream of the diode but it was -24VDC on other side. I am not sure what happened. I heard a noise and V3 was bluish and I killed power to variac. I attempted to reseat V3 and noticed that the base was cracked all around and loose. I gently pried and got it out but now I am wondering what to do. I will look but don't think I have any 7189 tubes. I have some EL84 and others but will need to dig around if something else would suffice for checking voltages and continuing.
    If not, I will order some tubes. Recommendations welcome.
    I may have bumped it inadvertently or it was cracked already? I removed and installed them once but didn't notice anything notable prior to this happening.

    Bill
     
  9. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    Sovtek EL-84M's are the modern equiv to 7189's. I pretty much abuse :whip:them in my X-202. Run the bias at 44v, and have the Volume set for 11:naughty::naughty: most of the time as I'm outside in the front yard. With the Klipsch Heresy's it comes in clear down at the mailbox about 40ft away with just the front door open, and the spkrs are in the next room.
     
  10. notdigital

    notdigital AK Subscriber Subscriber

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    Location:
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    There are a number of flavors of Russian tubes available for use in your SA-100. I picked up a couple of quads of 6P14P-EV at auction when I was doing my SA-100. I guess the word got out because they are now much more expensive than when I bought them just a few years back. Still less than GE's. The Sovtek's are pretty much the same tube but current manufacture.

    You might want to check the spec sheet for voltages: http://www.tubes.ru/techinfo/HiFiAudio/6p14pev.html.

    https://frank.pocnet.net/sheets/106/7/7189.pdf

    Nice job on your amp BTW :thumbsup:
     
    Last edited: Jun 15, 2018
  11. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    485
    Location:
    Pleasanton, TX
    Larry and Notdigital, I appreciate both your prompt responses. Thanks for compliment, not done but chipping away at it.....

    So, either the EL84M or the 6P14P-EV will work fine? Let me double check and make sure I don't have something here(doubtful).

    I will wait until I get one of those to continue unless I use the regular EL84 for checking voltages? Based on what I have read, I don't think I can or should. I was only asking as it would be cheaper to replace if there was an underlying issue that may have contributed to that tube failure.

    Thanks again.
    Bill
     
    Last edited: Jun 15, 2018

     

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  12. notdigital

    notdigital AK Subscriber Subscriber

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    If memory serves me, it's the same tube. Reflector, the manufacturing plant of the military 6P14P family of tubes, sold their stuff to Sovtek or New Sensor or whatever Russian Co. now makes the EL-84M tube referred to by Larry. You could really beat up the military version of the 7189 and IMHO they are perfect as test dummies due to their inherent ruggedness since they are uprated versions. Indeed, they are very good for long term use as well. If I recall they are some internal wiring differences between the 7189 and the Russian version but the differences are irrelevant in the SA-100 application.

    In my experience, it took some wrangling to get a quad to bias correctly but they were perfectly fine once properly balanced. I eventually stuck a quad of GE's in my amp for no reason other than getting a bunch cheap from another member. That said, I wouldn't hesitate to use them for permanent duty.
     
  13. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    485
    Location:
    Pleasanton, TX
    I am hoping to get back on this beast. My progress here was rudely interrupted by summer session for school. Now that that is done and I found a 7189 tube to replace the one that broke. I still don't know what happened to the first tube or if I broke it? I will do initial power up with the DBT . Then, I will try to get everything set up to redo all adjustments starting from scratch and take some voltage readings again tomorrow! A couple of questions for everyone....
    How long of a warm up time do i give it before taking voltages?
    I do not want to have any more setbacks if I can help it. I'm sure we all feel that way about our projects.
    Should I be concerned with that one voltage that seemed to be way off? It was between R56 and M1. It was 43 instead of 24 vac. but other side of diode(rectifier) was -26 according to my notes.
    Any other precautions I should consider?
    As always, I appreciate the input from everyone here

    Another question...I was reading threads and saw that some folks have ran 6BQ5 tubes with success. While, I don't want to do that forever, should I use those for initial setup as they are cheaper to replace if something is wrong. I have several of those lying around that I could use. Thoughts?

    Bill
     
    Last edited: Aug 15, 2018
  14. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    Bill -- as much as possible, take voltage readings as early as possible -- even while the unit is warming up -- this to check any potential problems before they can do any damage, or make any required adjustments in real time. Particularly the cathode current readings of the output tubes......

    Your voltage reading before the rectifier is correct -- as with numbers on the SA-300 schematic, the numbers here are transposed, with the likely intention of the indication being "42 VAC".

    The SA-100 will operate just fine with 6BQ5 tubes for testing, or for long term operation. Fisher always specified the latest production tube for a given product (even if it wasn't generally even available yet) -- this in keeping with their desire to keep their image always one step ahead of the game, or as the first to use the newest and latest, and therefore, greatest. At the time, that was the 7189 -- silk screened on even the chassis of the X-101ST before it was even in the RCA tube manual (so was the 7025). In reality however, either of these units will operate just fine with the 6BQ5, with no detrimental effects to the tubes at all.

    Good luck with it!

    Dave
     
  15. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    485
    Location:
    Pleasanton, TX
    Dave, thank you for all of that information. I searched around for schematic mistakes because I thought I read that somewhere before but didn’t find that info. I enjoy the background and information regarding the equipment. Great to know!!
    It will be comforting to do set up using 6BQ5 just to ensure everything is working properly.

    Also, this may be a basic question but what would be recommended way to measure cathode current?
    You say to do it quickly or ASAP upon applying power. So, I assume I need to find some easily accessible points to take readings.

    I don’t really have a dedicated current probe other than fluke 771 milliamp probe. I’d have to dig up specs though.

    I will see what I can come up with as I am just getting back into this but want to get her finished up soon if possible.

    Thanks again...
    Bill
     
  16. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

    Messages:
    9,787
    Location:
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    Fisher provides an external terminal strip for measuring the current through BOTH tubes of each channel. The terminals are normally shorted together during normal use, and then unshorted to make the adjustment. The terminal strip is located on the left side of the front panel, opposite the AC and DC Balance controls. The stock design should be adjusted for .6 vdc between each outside terminal and the center terminal (ground).

    Start with the DC Balance controls centered, then make the Bias adjustments. The DC Balance adjustments are ultimately supposed to be made for minimum hum in each channel, and then the Bias adjustments touched up for the correct indication. The adjustments are interactive, so you'll need to go through the process a number of times to get them all centered in on their final setting.

    Dave
     

     

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  17. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
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    Location:
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    Finally got a chance to sneak in and work on this. I was able to make adjustments. I went back and forth a couple of times. All seems good. Both A and B are set to .6 volts as well as DC balance of each at minimal hum.

    On a side note, I did attempt the dc balance adjustment using an analog meter but still couldn’t determine least deflection definitively. Maybe I was gong something wrong or didn’t know what I was looking for?
    I went back to headphone method and was able to hear an audible difference.


    Level set controls are still CCW(turned down).

    What next?

    Am I finally close to really listening to this thing?

    Bill
     
    Last edited: Aug 22, 2018
  18. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    Location:
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    The minimum deflection method works OK with an analog meter, but is next to impossible to do with a digital meter -- ergo, my suggestion to use headphones to make the adjustment.

    Time to start listening!!! Let us know how it turns out!

    Dave
     
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  19. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    485
    Location:
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    Yes!!! Finally got to hear this baby sing! It sounds great. I just used an iPod and some KLH 23 as that is what I had closest. Wow!

    I will run it springly but I plan to begin working on EFB next as it does produce some heat as others have mentioned.

    Thanks for all the guidance and support.

    I’ll definitely post some pics soon.

    Bill
     
  20. notdigital

    notdigital AK Subscriber Subscriber

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    I've been lazily restoring a 2nd SA-100 and, like my first one, it will be EFB'd. You won't regret the modification!
     
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