[ARC5] IF transformers - off frequency

[Leslie Smith]

Dear ARC-5 mail reflector

I am reviving or rescuing a much worked over Bc-453-B.  The detector and
AF stage work; I'm now in the process of making the IF system work.

Looking at the 1st IF stage I found that the transformer appears to be
resonant at 55 to 60kHz.  Using the same method I measure the resonant
frequency of the other two transformers as around 85kHz; this is as
expected from the figures given in the service manual.  The service
manual gives a procedure to align a set, but there is insufficient
adjustment available to raise the frequency to 85kHz.  

Opening the IF can I see nothing that seems abnormal.

(In contrast to this, I see the local oscillator coil has been
"fiddled".  I found a problem in the second IF transformer - but this
was fixed by shaking out a metal fragment hiding under the trimming
capacitor.)

Inside the can I see a second device, and this appears to be adjustable.
 The service manual does NOT mention this, but I suspect it is some kind
of capacitor, as the size of the trimming cap seems small for 85kHz.

Can any-one on the list say whether they have found un-fiddled
transformers off-frequency.  Ditto for the function of the second device
(that seems to be adjustable, and has a paint-locked screw on the top of
the IF can.  The simple solution would be to find a junked set, and
"rob" it of an IF transformer, but I would like to get this set going if
possible.  I have yet to get into the RF/mixer section, and I suspect I
will have REAL trouble here, as the local oscillator has been
"unwound/rewound".  I'm unable to "dip" the mixer tank circuit, and the
reason is unclear.

Thank you,


Les Smith
-- 
  Leslie Smith
  vk2bcu at operamail.com

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