B&W 5100b mod iron

[Detroit47]

This subject has been gone over before, but I still am unable to find out the specs for the original mod transformer. I have seen some peoples hypothesis on it but not the factory spec. I could just put any number of transformers in it but I was hoping to replace it with what the original design called for. I have a mod trans out of a Viking 2 and one out of a DX100 also one from a Valiant. I'm sure any of them would work. Having it rewound seems like a expensive proposition for a 100 watt transmitter. The transmitter isn't bad looking but it would cost more to rewind it than it is worth. Maybe I should dismember it and Ebay the parts.

John N8QPC

[N8ETQ]

   Hey John,



        Just went through that with a 5100B from a ham
in Va.  As much as you hear folk's worry about blown
mod iron, I really don't see many bad ones. I was
pretty surprised when this unit had all the "Gorey"
symptoms.  Therefor I took great pains to document
the Winding "R"'s and even whipped up a Megger!


        The 5100B mod iron has 6 leads, On the
modulator tube side he has a RED lead and two
leads with ceramic plate caps attached. One is
BROWN and the other was BLUE.

        The "R" I measured were:

   RED > Blue  128 ohm
   RED > Brown 119 ohm
   Blue > Brown 240 ohm.

       The PA side also has 3 leads, Yellow,
Black and Green. All these leads go to the
PLUG Assembly on the bottom plate.


    BLACK > Yellow 23.5 ohm
   Black > Green  40   ohm
   Green > Yellow 66   ohm

NOTE: The BLACK lead is not a center tap, It's
the 600 ohm tap.


        My customer procured a replacement unit
and I was surprised to find the "New" unit ohm'ed
out very much like the "Dead" unit.  But my HB
Megger "Told the Tale".  He was leaking on
the PA side to the case.  I'm glad my bench is
wood!

   
        With the replacement unit installed, he
worked fine and still is.  I was thinking afterwards
how rare it was to find a bad Mod. Xfmr and
recalled the only other one I had seen was also in
a 5100.  I'm thinking we had a spare from a Valiant
we put in there and he is still working FB. that was
back in the 80's...

 
Hope this helps,

73 es GL

/Dan

[N2DTS]

What is the big deal?
Even new the rigs often had a mis match and any multi tap universal mod transformer will have a mis match.
You are fine if a transformer is in the ball park and good for the power.

Its very easy to tell what the mod transformer should be, pair of 6146's at 700? volts and 220 ma? 3200 ohms.
6146 modulators in AB2 is 5 to 7.4 k ohms (500 to 750 volts).

So 3200 ohms to 6K at 100 watts would be nice.

The 5100 was a nice transmitter.

[N8ETQ]

   Yup,  I agree. "Close enough is gud enough".
Ironic though that the only bad Mod Xfmrs I've seen
were both on B&W 5100's..  Well built rigs with
top of the line components, but one has to wonder...
Add that to the OP's post... Even that puny POS
on a ranger is pretty stout for the "I" involved.

   It's not a big deal, but if it's bad, It's BAD...


/Dan

[Detroit47]

I know this little guy wont work, but I got to wonder what it is good for.

[VE3AJM]

An ART-13 mod transformer might work well in there, if you can find one.

Al VE3AJM

[N8ETQ]

  those T-195 Mod decks Fair had were a steal too..


/Dan

[N4zed]

It's a 1-2-3 block John....

[w4bfs]

It's a 1-2-3 block John....

one of the handiest things to have in a machine shop .... only thing better is more of them 

[Detroit47]

It could be a 25 x 50 x 75 block. I have parked most of my 1,2,3's unless it's just a build up. All of our machines are metric. I work for Chrysler as a Tool and Die maker. I still would like to know what the lil mod transformer is good for. I finally took my Extra test I'm now an Extra. Happy Thanksgiving day to all.

73 John N8QPC

[Opcom]

Interesting transformer.

People always think of the modulation transformer primary as being used CT, and 30K is a lot, but 30K CT is two 7500 Ohm windings put in series, so look at single ended class A data for a 6-8K load.

Consider if it were used as two primaries for class A amplifiers with 7500 ohm loads arranged in push pull. What tubes runs around 20-30mA and uses 300-600V?

Medium voltage tubes that are happy in class A at low currents like the 807 or better yet the 6BQ6 is likely more suitable and also cheap, and was used in a nice looking a 20-25W modulator in a Handbook article.

Low voltage tubes like the 6K6 and 6F6 also come to mind for milder applications as well as unusual kinds like the 6AD7G 6AC5 6AB6 6M6 7B5 41 42

25K 30mA secondary, maybe 15-20W audio rating is applicable.

[KA2DZT]

30K CT winding is two 15K windings in series.  Put the two 15K windings in parallel and it's 7.5K.  Of course, you can't put a CT tap winding in parallel.

Fred

[w8khk]

30K CT winding is two 15K windings in series.  Put the two 15K windings in parallel and it's 7.5K.  Of course, you can't put a CT tap winding in parallel.

Fred

Looking at the diagram and external terminals, it appears that the secondary windings are connected in series internally; so there may be no option to put them in parallel.

[w4bfs]

connections on the secondary in that manner seem to demonstrate an effort to minimize leakage reactance which would extend high freq response with less phase shift ...if so a 3khz upper limit should be very conservative and should sweep out much better .... looks like a class ab1 driver to me

[Opcom]

I didn't see the post about a 15K primary arrangement or a secondary tap. There appear to me no such solutions with the transformer as-marked but I can be wrong.

Putting the two 7500 Ohm primary windings in series by connecting 2-3 gives a 30K center tapped primary.
The total Z is the single winding Z exponent the number of equal windings.

The object of the post about the little transformer was to suggest a way to use the it. It's rated 30mA and 1275V RMS test. That suggests a plate voltage range of 500-600VDC with a good safety factor. 10-15W plates would be happy.

The secondary impedance and current rating suggests about 750V RMS on that winding and if so 22.5W is reasonable.  It could possibly modulate a smaller transmitting tube like a 2E26 or for UHF an 8025 or 8012.

Class AB1 driver with a tapped resistive load on the secondary would be very interesting for lots of volts.

Alternately there are a lot of screens on larger tubes begging for a good quality transformer.

[KA2DZT]

Interesting transformer.

People always think of the modulation transformer primary as being used CT, and 30K is a lot, but 30K CT is two 7500 Ohm windings put in series, so look at single ended class A data for a 6-8K load.

Consider if it were used as two primaries for class A amplifiers with 7500 ohm loads arranged in push pull. What tubes runs around 20-30mA and uses 300-600V?

Medium voltage tubes that are happy in class A at low currents like the 807 or better yet the 6BQ6 is likely more suitable and also cheap, and was used in a nice looking a 20-25W modulator in a Handbook article.

Low voltage tubes like the 6K6 and 6F6 also come to mind for milder applications as well as unusual kinds like the 6AD7G 6AC5 6AB6 6M6 7B5 41 42

25K 30mA secondary, maybe 15-20W audio rating is applicable.

Patrick,

What xfmr are you talking about??  It must be a special type.  Unless I'm wrong, as far as I know two 7.5K windings in series results in a 15K winding.  There are no exponents in the calculation. 

Now if you are talking about xfmr turns ratio.  Impedances would be related to the square of the turns ratio.

I'll think some more about what you're saying, maybe I'm wrong and you're right.

OK, I thought about it.  I guess if you hold the load on the secondary constant and the turns ratio of the xfmr reflects back to the primary a 30K CT impedance, if you then only use half of the primary, the reflected impedance would be only 7.5K.

OK you're right.  I think this was a trick question designed to confuse old people.

Fred.

[W4RFM]

OK you're right.  I think this was a trick question designed to confuse old people. Grin

Oh Lord, I am in trouble then....

[W3RSW]

Well it distinctly says " modulation transformer. "
So not over thinking it, I'd try a pair of 15e's modulating a single 15E.  Tie a common on the primaries to see if a CT arrangement works for the AF.
Would be one cute little devil.

2000 volts at 10ma yields  20 biggies input, say about  10 to 15 watts output class C.

And on a plus side, good for high altitude.