Mystery transformer

Discussion in 'Technical' started by N1BUS, Sep 4, 2016.

  1. N1BUS

    N1BUS Member

    I have a transformer labeled F 78 D on the bottom. It has a center tapped primary and a center tapped secondary. Both sets of windings have a couple hundred ohms resistance making me think its a modulation transformer or an interstage driver transformer. There is no manufacturer label on it and I don't know if someone painted it and covered up the manufacturer name. I googled it but could not find anything on it. Does anybody Have any data for this/ Sincerely Steve, N1BUS.
     
  2. WD5JKO

    WD5JKO Member

  3. W5HRO

    W5HRO Administrator

    With a hard case like this uploading some pics of the transformer is always a must and helpful too.
    .
     
  4. N1BUS

    N1BUS Member

    OK I took some pictures. This is an odd one that tapers slightly. I wonder if its a foreighn transformer. This came from a modulator that someone had built. The other transformers in it were Stancor and had the stancor label on them. this one is only marked on the bottom with F 78 D. The primary measures 313 ohms from terminals 1 to 2. 134 ohm from CT to 1 and 181 ohm from ct to 2, The secondary measures 6.884k from 3 to 4. 2.904k from ct t0 3 and 3.905k from ct to 4. It has a turns ratio of 1 to 4. If I feed 4.8 volts at 1000hz into 1 and 2 I get 19.21 volts from 3 to 4.

    modu2 (1).jpg modu2 (2).jpg modu3.jpg modu4.jpg modu5.jpg
     
  5. W5HRO

    W5HRO Administrator

    What kind of tubes did the modulator have in it or do you even know?

    From your voltage description it sounds like a step-up transformer, but it may just be the numbering unless the circuit needed a step-up ratio which sometimes did happen, like with screen modulation for example. It could be a step-down with 1 & 2 being the output side. From the pics it would appear to maybe be an audio driver transformer unless the modulator used smaller type final modulator tubes. It could be for the final modulator then it could also just be a power or bias transformer. Hard to tell.

    That F78D on the bottom is probably the model number though for sure.
    .
     
  6. N1BUS

    N1BUS Member

    It was a pair of 6L6 tubes. The metal ones.
     
  7. N1BUS

    N1BUS Member

    Thank you everone for your help with this. I did some more searching today and found a Kenyon transformer catalog on the bunker of doom site. The shape fits a kenyon transformer but I dont see this one in any of the catalogs. I suspect this was built during WW2 judging by the age of the components and the odd way things were wired. It appears whoever built this used audio transformers for chokes and had to use whatever they had to work with.
     
  8. W5HRO

    W5HRO Administrator

    No problem, I couldn't find that number listed anywhere either. That transformer is the right size for 6L6's and it probably is an audio transformer due to it having center-taps on both sides, but the ratio? It might work if you reverse it or use it to modulate the screens of two RF tubes in push-pull.
    .
     
  9. N1BUS

    N1BUS Member

    I wonder if it could be a driver transformer for another modulator stage. using the step down side to drive the grides of a 500 watt audio amp.
     
  10. W5HRO

    W5HRO Administrator

    Could be. That was my first though, but you said the 6L6's were the modulators. Could have been either or...
    .