Quick and Easy 400 Phase Inverter Adjust.

Discussion in 'Fisher Forum Stickies' started by larryderouin, Dec 1, 2013.

  1. Tom B

    Tom B AK Subscriber Subscriber

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    500c Phase inverter adjustment

    I have a 500C, and 800C I am doing some FM alignments on. I am also looking to do the phase inverter adjustments.
    While I don't possess a Distortion meter/analyzer, I do have a very nice dual trace Textronics scope, and a very good Signal Generator.
    Is there a way I can inject a signal and using the scope, view and adjust the phase inverters for minimal THD?? If there is a way, what frequency or tone should I inject.
     
  2. larryderouin

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

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    Apparently you either use the procedure outlined in the Executive 960 manual (1964 Executive Console) (with a Scope and an IM Distortion analyzer or the simplified procedure outlined above.

    It takes me approx 5 minutes to set up a 800-C using the above procedure. Very quick, and easy. By matching the resistance between the sides, I imagine you null out most if not all IM Distortion.
    ScreenHunter_71 Mar. 13 09.29.jpg
    [​IMG]

    This procedure is also in the 30001 and up, and the 30001-49999 manuals.
     
    Last edited: Jan 17, 2017
  3. larryderouin

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

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    One more thing. Replacing resistors (on the 400) R101,103,109&111 for V12 and
    R102, 104, 110, 112 with matched 1% resistors will result in a tighter adjustment. I was able to get them to match exactly on both sides, to 1 decimal place (meter allowance). And they held for the time I had Tom Nichols unit (over 2 weeks).

    Larry
     
  4. fdwrench

    fdwrench Active Member

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    Hello,
    I am working on a 500c.
    Adjusting the phase inverter control changes the value at pin #1 while Pin #3 stays constant.
    Is our goal to get the value of 1 & 3 the same?
    Thank you

    Ed
     
  5. larryderouin

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

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    The goal is to match pin #3 with pin 1. Make sure you ground the appropriate B+ supply (POWER OFF!!!!!! and UNPLUGGED!!!!!) before testing.
     
    Last edited: Aug 29, 2014
  6. keithpgdrb

    keithpgdrb Super Member

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    help. seem to be having a similar problem to fdwrench. when connecting to pin 3, the phase adjust dial does nothing. It does move the readings at pin 1 though.

    Please clarify. I am assuming we have to match the pins. if only one of the pin readings moves, isn't that the one to adjust? If so, that is not the way it reads in the instructions. if not, what is wrong here? I have the correct B+ grounded to chassis.

    and yes, it is powered off and unplugged.
     
  7. larryderouin

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

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    Guys; Just match the #'s. It's possible that FISHER made changes during production. If your unit serial # is different than I alluded to in the instructions the manual may be different. I DO NOT have access to the manuals other than those listed above in Post #1.

    It is possible that FISHER changed the pot connections from pin 1 to pin3, which IMO, doesn't make a real difference as long as the #'s match when you adjust it. I had this happen on the 400 I did last (64000 series).

    Keith what's the serial # of your 500-C and do you have the matching manual, you can screengrab that section of the schematic and post it?

    I'll get with Dave on this but I feel from past exposure to this it's probably a non starter.
     
    Last edited: Oct 16, 2014
  8. keithpgdrb

    keithpgdrb Super Member

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    500C serial 58428 s

    ironically, the schematic that came with the unit is the one from 30001-49999. So not helpful at all really for this situation.
    [​IMG]
     

    Attached Files:

  9. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    Keith -- When I developed this procedure for setting the phase inverter adjustment without the use of distortion measuring equipment, it was at a request from Larry who was working on a Fisher 400 receiver at the time, and asked if I would develop an alternate approach for him to use. Therefore, the procedure I wrote up for him was necessarily directed towards that particular unit. At the time however, I had no idea the procedure would end up as a sticky for general use with all of Fisher's pieces that include such a control, so with that reality, confusion could certainly result.

    Ultimately however, the procedure will in fact work for all of Fisher's receivers, but as you noticed, the terminal that represents the fixed value, and the one that is adjustable is different in different units. As surmised, in the 400 receivers, the phase inverter adjustment control appears in the cathode circuit of the inverter, while in the 500B/C and 800 B/C units, it appears in the plate circuit. This means that in some models the pins react as the procedure is written, while in others, the action at the terminals is reversed.

    The same situation is present in their amplifier series as well, with some units having the phase inverter adjustment control on one side of the inverter, and some having it on the other.

    The good news is that the basic process still works, regardless of which side of the circuit the control appears on. One terminal will always represent a fixed value, and one terminal can be adjusted, with the control always being adjusted to make the two values equal with the temporary ground in place.

    As for the point to temporarily ground when making the adjustment, it will always be the power supply point providing power to the phase inverter tube. It will represent a B+ source of different voltage levels in different units, but regardless of the voltage level the source represents, it is always THAT source which is temporarily grounded.

    Finally, in an effort to make the procedure as truly universal as possible, one other factor may come into consideration with some units: Fisher primarily used a dual triode tube as the phase inverter tube -- being either a 12AX7, or 7247. While the terminals used for this adjustment procedure have always targeted the section employing pins 1 and 3, it is entirely possible that some models may use the section employing pins 6 and 8 for the phase inverter function. Again, the procedure still works just fine, but the pins used would be different. If this situation presents itself, it can best be resolved this way:

    Between the four possible pins involved (1 and 3 OR 6 and 8), simply determine which one the phase inverter control acts to adjust the resistance of when the B+ supply point to the phase inverter stage is temporarily grounded. Once that terminal is determined, then you will know which other terminal is the "mate" to represent the fixed value for the procedure, whereupon the process can then be carried out in the normal fashion.

    Finally, there were a VERY few Fisher models that used a 7199 tube for phase inverter service. Those units will ALWAYS use pins 1 and 8 to implement the procedure, with one of those terminals representing the fixed value, and one which can be adjusted. Otherwise however, the process is the same.

    I suppose a list could be generated by model, identifying the point to temporarily ground, which terminal represents the fixed value, and which is the terminal to be adjusted, but in the absence of that, understanding the basic points I've presented here should help most to implement the procedure easily enough.

    Good luck with your Fisher, and I hope this helps!

    Dave
     
  10. larryderouin

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

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    Thanks Dave. I thought it might be something simple, but wasn't sure about the specifics as it worked either way and i didn't really think about it at the time on the 800-C's.

    Larry


    To add to Dave's previous post, I went thru the manuals for the 400, 500(mono), 500-S, 500B/C, 800B/C, TA-600, and TA-800. I've listed which Phase Inverter tube pins are actionable , and what they do.

    STATIC MEANING you check and note the RESISTANCE!
    ADJUSTABLE meaning the pot is connected to this pin and you adjust this PIN to match the Static pin.

    400, 12ax7 Driver, Pin 1 is STATIC, Pin 3 is ADJUSTABLE

    500 (MONO) 12ax7 Driver, NON ADJUSTABLE, NO P.I. POT

    500-S, 7247 Driver, Pin 1 is STATIC, Pin 3 is ADJUSTABLE

    500-B/C, 12ax7 Driver, Pin 1 is ADJUSTABLE, Pin 3 is STATIC

    800-B/C, 12ax7 Driver, Pin 1 is ADJUSTABLE, Pin 3 is STATIC

    1800, 12ax7 Driver, Pin 1 ADJUSTABLE, Pin 3 is STATIC (1800 is a 800-C with 2-tone face plate)

    TA-600, 7247 OR 7199 Driver, ALL VERSIONS! NON ADJUSTABLE NO P.I. POT!

    TA-800, 7199 Driver, Pin 1 STATIC, PIN 8 ADJUSTABLE.
     
    Last edited: Apr 24, 2015
  11. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    Perfect Larry -- although you might edit your sentence defining "static" to indicate resistance, not voltage.

    Dave
     
  12. keithpgdrb

    keithpgdrb Super Member

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    Thank you both. Couldn't really get any more clear then this. It will surely help the less electronically knowledgable like myself.

    I really should take a basic electronics course. I enjoy fiddling around.
     
  13. keithpgdrb

    keithpgdrb Super Member

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    Hey guys, I will probably start a new thread on this. But when adjusting the phase pot, I can't get the value low enough to match pin three.

    My values were 52.47 ko on the right. 51.98 ko on the left. Both my pots were set in the 60's. When I dialed them down, I got to about 54.4 on the right, and 53.0 on the left.

    Any ideas why?
     
  14. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    Make certainly you are grounding the correct B+ supply point. Based on the schematic, it is the point that feeds the center terminal of the phase inverter adjustment pots.

    Dave
     
  15. keithpgdrb

    keithpgdrb Super Member

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    C91C right? one of the silver can caps right? not the black paper covered can right? I swear I'm doing it right. I'll double check though. nothing good happens when I swear.
     
  16. larryderouin

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

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    Yeah C91C. find the wire from the Center tap on the pot, and follow it back to the can cap. No sense in telling you its a certain color, as I've seen red, orange, dark blue, green wire.
     
  17. keithpgdrb

    keithpgdrb Super Member

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    Yeah, ok, so I was on the wrong part of the can cap. I have non original can caps, and I was going by the voltage written on the side. Thank you for the instructions on which wire to follow. Dialed it in with no problem. after it was hooked up right. Glad I did this, but what a pain it turned out to be. Time to button it up and leave it that way for a while.

    Blue wire by the way. lol.
     
  18. PaulWC

    PaulWC Member

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    Procedure for X-1000 (X-101 ST)

    I did the adjustment on my X-1000 (X-101 ST) in my '59 Executive III. The tube pins are 1 (measure) and 3 (adjust) with the the C34-A capacitor grounded. Easy to do and boy did it need it. Thanks for the procedure.
     
  19. RUmad

    RUmad Well-Known Member

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    Gentlemen, how about on an x-101-c? Seeing how chassis isn't actual ground. I wasn't even going to mess with the PI pots until I read this. Seems like a simple enough process, except for the elevated ground issue.

    Alan
     
  20. RUmad

    RUmad Well-Known Member

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