[Milsurplus] DAV IF issues

[WA5CAB at cs.com]

Ray,

The DAV-2 Instruction Book that I have a copy of gives a remarkable amount of 
information on the IF transformers.  Unfortunately, some of it is clearly 
incorrect.  But the primary of your Z-101 (Input IF Transformer) is definitely 
bad.  According to the detailed information table, the primaries of both 
transformers are 510 turns of 5-44 S.S.E. Litz Wire.  DC resistance given is 30 ohms. 
 Both secondaries are listed as 600 turns of the same wire and DC resistance 
listed is 26 ohms.  Which figures don't agree with the turns/wire size of 
course.  Table also gives inductance and AC impedance.  And says the fixed padders 
on the primary and secondary are 45 uufd and 30uufd respectively.  There are 
obvious discrepancies in the inductance figures but the impedance figures tend 
to agree with the stated turns counts.

And despite both transformers being said to have the same turns counts they 
have different part numbers.  However, that could simply be because they are 
marked externally by location.

Bottom line is that if you are actually getting 10K ohms across the first 
primary, that's not what it should be, regardless of what the correct figure 
actually is.  I don't know why it doesn't just show as open.  When one of the IF's 
in a BC-611 goes open, the reading goes to several megohms, depending upon 
how much MFP varnish was globbed over the surrounding wiring.

Anyway, before discarding the 1st IF transformer, you should remove it and 
open it up and look at where both wires come out of the primary.  When this 
happens to a BC-611-F transformer, sometimes the break will be right at the solder 
terminal instead of flush with the surface of the coil.  And with care, you 
can repair it.

In a message dated 9/10/2007 10:26:48 AM Central Daylight Time, 
rafantini at salisbury.edu writes: 
> There are two IF transformers, an input
> transformer between the 1R5 and 1T4 and an output transformer between
> the 1T4 and the 1S5 the detector and first audio. The output IF
> transformer peaks with both top and bottom slug right in the center just
> about where they started out but the input transformer had to have both
> top and bottom slug turned all the way in and the transformer peak
> output is greatest when both slugs are this way. No peak just maximum
> output with full in. When I started the slugs were just about the same
> location as on the output transformer. I suspect something is not right
> with this transformer but have limited experience with battery powered
> IF stages. I looked at the resistance of the primary windings of the
> transformer in question and it read around 10 K in compression with the
> output transformer that has a primary or plate side resistance of around
> 50 ohms. The 1R5 pentograde converter only draws about 0.7 to 1.4 Ma
> total plate current so maybe the high resistance is normal for the
> transformer. Also it has been proposed that I open the IF transformer
> and check the capacitors across the windings. Although have to wonder if
> they ever fail? So if anyone has any ideas on what the normal
> sensitivity of a four tube radio should be, or experience of IF
> transformers that appear not to be resonate, or ideas of just what the
> resistance of the first IF transformer should be please don’t hastate
> to respond.

Robert & Susan Downs - Houston
<http://www.wa5cab.com> (Web Store)
MVPA 9480
<wa5cab at cs.com> (Primary email)
<wa5cab at comcast.net> (Backup email)
   
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