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    FM3 EMM801 tube operation

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    eickmewg

    Posts : 38
    Join date : 2014-08-29

    FM3 EMM801 tube operation

    Post by eickmewg on Mon Mar 21, 2016 6:35 pm

    I found a Telefunken EMM801 tube for a reasonable price and decided to get it for my FM3. It was advertised as NOS/NIB and it does appear to me to be unused and it does have the Telefunken diamond on the bottom of the tube. My question deals with the degree of closure for the lower tuning portion of the tube. My old EMM801 would close fully when first turned on and tuned but then would open a little as the tuner warmed up. With the new EMM801, maximum closure for both moderate and strong signals leaves the space between the two innermost vertical lines open, about 1/16th of an inch. The "stereo" indicator on top closes fully with a stereo signal. So, how should a brand-new EMM801 operate? I guess with the new tube, optimal tuning is a little easier to see when there isn't full closure. So, how is this thing supposed to work?

    Bill

    GP49

    Posts : 717
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    Re: FM3 EMM801 tube operation

    Post by GP49 on Wed Mar 23, 2016 1:14 am

    The lower bar is not supposed to close completely.

    eickmewg

    Posts : 38
    Join date : 2014-08-29

    Re: FM3 EMM801 tube operation

    Post by eickmewg on Wed Mar 23, 2016 6:14 am

    I was hoping this to be the case. So "maximum closure" need not be "complete closure" and it all makes sense. One thing I did note is that the new tube is considerably brighter than the old tube. I will now put my mind at rest and enjoy my fine FM3.

    GP49

    Posts : 717
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    Re: FM3 EMM801 tube operation

    Post by GP49 on Thu Mar 24, 2016 9:34 am

    Passive circuit changes in the feed from the AGC line to the appropriate control grid on the EMM801 can be done to tweak if necessary but the whole intent of the circuit is to provide a visible peaking even at very high signal strength. That won't happen if it closes fully. Yours is working properly. Enjoy it!

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    Re: FM3 EMM801 tube operation

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