[Boatanchors] What Are the Differences Between Input, Interstage, Output IF Transformers?

[Richard Knoppow]

    Older tweet filters were tuned for 10Khz since, in the U.S. 
AM stations are assigned every ten KC. Even when an adjacent 
station is week it can produce a strong 10Khz beat. Especially in 
high fidelity receivers the tweet filter is necessary. Some are 
at RF in the IF stage but often they were audio filters. A 10Kc 
filter in the IF requires very careful tuning and works only when 
the signal is centered in the IF, an audio filter always works.
    Its possible the "tweet" filter here may be something else. 
For instance, some receivers have a filter in the RF stage to 
null out the IF frequency.
    The term "tweet" is often used to indicate beats caused by 
harmonics of the local oscillator that beat with received 
stations or result in the IF frequency. They are tunable. 
Sometimes the results of coupling in the power supply.

On 10/11/2021 12:57 PM, Al Klase wrote:
> Scott,
> 
>  From J.W. Miller Catalog 38:
> 
> Intermediate frequency transformers
> require different degrees of coupling for
> various circuit applications, and these
> are coded as follows:
> 
> No.1 Input Stage - Has coupling adjusted
> for maximum selectivity and
> is for use between the mixer and the
> first l.F. amplifier tube when two or
> more stages are used.
> 
> No. 2 "Interstage - Designed to be used
> as the interstage transformer' in a
> two stage amplifier or as the input
> stage for a single stage amplifier.
> Coupling is adjusted to the optimum
> degree. May also be used as the
> output transformer in an amplifier
> in which the second detector is a
> non-current consuming load, such as
> a bias detector of any type.
> 
> No.3 Diode Transformer - For use as
> the output transformer to feed any
> full-wave diode · detector circuit.
> The secondary is center tapped 10
> provide equal voltage to both dbde
> plates. Adjusted to provide overcoupling
> in order l'::> prevent excess
> ive selectivity, which would result
> in poor audio quality.
> 
> No. 4 Diode Transformer - This trans~
> ormer is similar to the No. 3 type
> except that no center tap is provided.
> No.5 Beat Frequency Oscillator-An efficient
> electron-coupled type beat
> frequency osci"llator transformer for
> CW use and for simplifying the logging
> of DX stations.
> 
> No. "CF" Crystal Filter Transformers These
> transformers are sold in pairs
> for use in crystal filter circuits of
> amateur and commercial receiveTs.
> They replace the regular input transformer
> and are of the low impedance
> link coupled type.
> 
> RE:  Tweet Filter from 
> https://www.sciencedirect.com/topics/engineering/passbands 
> <https://www.sciencedirect.com/topics/engineering/passbands>
> 
> "Some receivers use audio filters rather than IF filters to help 
> reduce the heterodyne squeal. In the AM broadcast band, channel 
> spacing is typically 8 to 10 kHz (depending on the part of the 
> world), and the transmitted audio bandwidth (hence the sidebands) 
> are 5 kHz. Designers of AM BCB receivers usually insert an R-C 
> low-pass filter with a −3 dB point just above 4 or 5 kHz right 
> after the detector in order to suppress the audio heterodyne. 
> This R-C filter is called a “tweet filter” in the slang of the 
> electronic service/repair trade."
> 
> Regards,
> Al
> 
> On 10/11/2021 2:26 PM, whitebear1122 at comcast.net wrote:
>> Hi, What are the differences between input, output, and 
>> interstage IF
>> transformers?  Then what the heck is a 455 KC Tweet Filter?  
>> Thanks. 73
>> Scott WA9WFA
>>
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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL