[Boatanchors] Super Pro Help! - Transformer Needed

[Richard Knoppow]

----- Original Message ----- 
From: "Robert Goff" <robert.h.goff at gmail.com>
To: "boatanchors" <boatanchors at mailman.qth.net>; 
"milsurplus" <milsurplus at mailman.qth.net>
Sent: Thursday, September 25, 2014 6:32 PM
Subject: [Boatanchors] Super Pro Help! - Transformer Needed


> Picked up a Hammarlund Super Pro with PS at the last 
> hamfest.  I'd
> really like to get this one up and running since it is the 
> 200X
> version covering the BC band and 160m.
>
> The one thing missing, strangely enough, is the audio 
> INPUT
> transformer.  This is single 6F6 to push pull 6F6's.  A 
> look through
> my junk box yielded nothing even close.
>
> Anybody have a junker Super Pro with this transformer? 
> It's T-7 on
> the schematic in TM 11-866.
>
> Thanks,
> de Robert W7MKA
>
> PS.  This particular receiver, although it has civilian 
> markings does
> have orange Signal Corps stamps and MFP varnish - applied 
> (as the
> stamp says) Jan '52.  Panel is black and that seems to be 
> the original
> color.  I'm guessing this was a very late pre-war 
> production?

    The transformer specs can be found in military handbook 
TM11-866. I found this on the web but no longer remember 
where.
    The driver transformer is Chicago Transformer type 
4212-C  Primary 3000 ohms impedance, secondary 
center-tapped, 34 ma, ratio 14:1  Although the current 
appears to be given for the secondary its probably for the 
primary since the secondary is connected to the grids of the 
output tubes and should have no current through it. RCA tube 
handbook RC-14 indicates that a triode connected Class-A 6F6 
under the conditions it operates in the Super-Pro will have 
a maximum plate current of 35 ma so the ratings seem about 
right although they give the load impedance as 4K ohms. 
Note that the output amplifier runs in Class AB2 which means 
it will draw some grid current on peaks.
    I gave the Chicago Transformer model number in case you 
have some sort of cross-reference to other makes. The 
arrangement of the audio amp in the Super-Pro was not too 
unusual.
    I don't know where to obtain an equivalent transformer 
but at least you have a clue as to what to look for. I hope 
this is of some help.



--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com