IF Alignment.Codar CR-70 - UK Vintage Radio Repair and Restoration Discussion Forum

gezza123 · 22nd Jul 2010, 9:52 pm

HY Guy,s
My Codar CR-70
Test Before Alignment.

First I found the IF frequency .IE: 470 Kc/s Then I tuned the radio to a known station Magic radio at 1548.I Then did a quick calc of 1548+470=2018Kc/s. I then connected the frequency counter to the Triode grid of the oscillator valve V1 and got a frequency of 2019Kc/s.So I then transfered
the frequency counter to the last IF detector and got a frequency of 471Kc/s.Witch would calc correct +-.%
So my question!)
Is my Receiver IF,stuned correctly,and is my ocsillator running at the correct frequency.so I no need to retune my IF,S.
I have just done the same test again on my newly aquired Ferranti 146 that read 2023 Kc/s and my IF,S read 475Kc/s.so is this a good way to test
your sets alignment before you dive in with the generator.

Gezza

G8HQP Dave · 22nd Jul 2010, 10:12 pm

Your test confirms that the IF is about right, although not necessarily perfect. It says less about the RF alignment, merely that the RF is close enough that signals can be received. A strong station would push past a misaligned RF stage. Strictly speaking all you have confirmed is that your IF response has a peak somewhere near 471kHz.

Bear in mind also that attaching test equipment can shift an oscillator slightly off frequency.

gezza123 · 23rd Jul 2010, 9:09 pm

HI.Dave thanks for the quick response,(yes) you were correct so I have now reset my ferranti I.F to 470Kc/s and peaked the I.F,s,the only difference I can find is that the counter set with a high compensation probe gives me an offset of about 3 to 5 Kc/s when I measure the oscillator frequency at the grid of the triode,if I connect at the anode of the triode then it gives me the correct frequency,this may have something to do with the mixing.thanks for the reminder I never gave any thought to offset,only the channel frequency offset,I have never set up a radio alignment before with a signal generator and was confused about the four mixed frequencies.
Thanks again the Ferranti is now superb and now needs cleaning,another job .

Gezza

22nd Jul 2010, 9:52 pm	#1
gezza123 Heptode Join Date: Mar 2010 Location: Eastham, Wirral, Merseyside, UK. Posts: 788	IF Alignment.Codar CR-70 HY Guy,s My Codar CR-70 Test Before Alignment. First I found the IF frequency .IE: 470 Kc/s Then I tuned the radio to a known station Magic radio at 1548.I Then did a quick calc of 1548+470=2018Kc/s. I then connected the frequency counter to the Triode grid of the oscillator valve V1 and got a frequency of 2019Kc/s.So I then transfered the frequency counter to the last IF detector and got a frequency of 471Kc/s.Witch would calc correct +-.% So my question!) Is my Receiver IF,stuned correctly,and is my ocsillator running at the correct frequency.so I no need to retune my IF,S. I have just done the same test again on my newly aquired Ferranti 146 that read 2023 Kc/s and my IF,S read 475Kc/s.so is this a good way to test your sets alignment before you dive in with the generator.Gezza

22nd Jul 2010, 10:12 pm	#2
G8HQP Dave Rest in Peace Join Date: Sep 2008 Location: Solihull, West Midlands, UK. Posts: 4,872	Re: IF Alignment.Codar CR-70 Your test confirms that the IF is about right, although not necessarily perfect. It says less about the RF alignment, merely that the RF is close enough that signals can be received. A strong station would push past a misaligned RF stage. Strictly speaking all you have confirmed is that your IF response has a peak somewhere near 471kHz. Bear in mind also that attaching test equipment can shift an oscillator slightly off frequency.

23rd Jul 2010, 9:09 pm	#3
gezza123 Heptode Join Date: Mar 2010 Location: Eastham, Wirral, Merseyside, UK. Posts: 788	Re: IF Alignment.Codar CR-70 HI.Dave thanks for the quick response,(yes) you were correct so I have now reset my ferranti I.F to 470Kc/s and peaked the I.F,s,the only difference I can find is that the counter set with a high compensation probe gives me an offset of about 3 to 5 Kc/s when I measure the oscillator frequency at the grid of the triode,if I connect at the anode of the triode then it gives me the correct frequency,this may have something to do with the mixing.thanks for the reminder I never gave any thought to offset,only the channel frequency offset,I have never set up a radio alignment before with a signal generator and was confused about the four mixed frequencies. Thanks again the Ferranti is now superb and now needs cleaning,another job . Gezza