[R-390] The R-390A IF transformers internal resistors.

[Gary I. Biasini]

Jacques,

I have a Stewart Warner R-390a from the same order number and with the
following IF module:

IF Module:
Make: 			Stewart Warner 
Order Number: 	42428-PC-59-A1-51
Serial Number:		477

Unfortunately, the unit is in Arizona and I am in Edmonton, Alberta.  When
(if?) I next go to Arizona, I will take a look and let you know what I find
out.  I took a quick look at Perry Sundeen's ultimate upgrade schematic and
there are no values shown for R511, R512, R553 and R554.  So, the mystery
remains.

Best regards,

Gary

-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
On Behalf Of Jacques Fortin
Sent: September 25, 2020 9:15 AM
To: Gary Biasini <gary.biasini at shaw.ca>
Cc: Collins R-390 HF Receiver List <r-390 at mailman.qth.net>
Subject: [R-390] The R-390A IF transformers internal resistors.

Hi all,

 

I am still working on the last R-390A that followed me home.

This one came with a Stewart-Warner IF deck (Order # 42428-PC-59-A1-51).

When I began to check everything into, it became obvious that a previous
"owner" removed all the resistors within the IF transformers.

The windings test all OK and the caps looks like the original ones, so it
may have been an attempt to "boost" the IF gain.

My question now is: what are the proper values of those resistors ??

I checked for the ones used in my Moto '56 and in a spare IF deck from
Capehart '61 contract and the results were:

Moto '56: R511, 512, 553, 554 : 47k ohms R522: 82k ohms.

Capehart: R511, 512, 553, 554 : 39k ohms R522: 68k ohms.

 

So, why there is a difference between the different makers / contracts ?

Which values should I use in the Stewart-Warner ??

I was unable to find anything in the Wu Li's "Pearls" section.

Does somebody already had documented these values somewhere ?

 

73, Jacques, VE2JFE

 

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