Replacing FETs in a 1970s vintage receiver--Need Advice--What is"Noise Figure" and "Gain" in regards to specs?
 

I'd like to replace 3 2SK19 FETs in a 1970s vintage solid state
AM/Shortwave receiver to see if it improves reception and overall
performance. When looking around the web for possible replacements or
substitutions, I compiled the list below (not sure if they are all
compatible, but they look like they should be).
Should I try to replace strictly with the same part number or should I
try to improve the performance by choosing a "better" FET. I know how a
FET works but I am not familiar with the specs listed below each type.
For example how does Noise Figure and Gain play into the performance
(Sensitivity) of the receiver?
I'll take any advice, suggestions or links to sites that can shed more
light on this topic...

By the way, I didn't want to xpost this message, but if there is a
better newsgroup to discuss this on please let me know. Thanks.

Regards,
Malomarski

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2SK19 Micro Electronics- a fet designed for FM tuner and VHF amplifier
applications
N-CH J-FET
Max Vds 18V
Max Id 10mA
Max Dissipation 200mW
Reverse Transfer Capacitance Crss 0.45-0.65 pF
Gain N/A?
N/A? MHz

---------------------------------------------------
2SK427 Sanyo - for AM tuner RF amplifiers and low-noise amplifiers
featuring ultralow noise figure
N-CH J-FET
Max Vds 15V
Max Id 10mA
Max Dissipation 200mW
Noise Figure 1.5dB
---------------------------------------------------
2SK161 Toshiba -FM tuner applications featuring low noise figure and
extremely low reverse Transfer Capacitance
N-CH J-FET
Max Vds 18V
Max Id 10mA
Max Dissipation 200mW
Reverse Transfer Capacitance Crss 0.1 pF
Gain 18dB
100MHz
Noise Figure 2.5dB
100MHz
-----------------------------------------------------
2SK192A Toshiba- FM Tuner applications VHF band amplifier applications
N-CH J-FET
Max Vds 18V
Max Id 10mA
Max Dissipation 200mW
Reverse Transfer Capacitance Crss 0.65 pF
Gain 24dB
100MHz
Noise Figure 1.8dB
100MHz

O. Alvarez wrote:
I'd like to replace 3 2SK19 FETs in a 1970s vintage solid state
AM/Shortwave receiver to see if it improves reception and overall
performance. When looking around the web for possible replacements or
substitutions, I compiled the list below (not sure if they are all
compatible, but they look like they should be).
Should I try to replace strictly with the same part number or should I
try to improve the performance by choosing a "better" FET. I know how a
FET works but I am not familiar with the specs listed below each type.
For example how does Noise Figure and Gain play into the performance
(Sensitivity) of the receiver?
I'll take any advice, suggestions or links to sites that can shed more
light on this topic...


Generally speaking, noise figure of a front end on an HF receiver, isn't
of much consequence. The HF bands are so noisy that most any modern FET will
be orders of magnitude quieter than what is required.

You might be able to get some improvement by finding a fet that is somewhat
higher gain, but I doubt it. Most likely, all you will succeed in doing is
creating an oscillator.

Where you can really improve things in HF receivers is to make sure that
the RF preamp is capable of very wide dynamic range, ending in watts of power
at the mixer. Then pick a good high level DBM that can handle a watt or so
of RF power without excessive compression. This will give you a receiver
that can handle high power adjacent channel signals without losing an on
channel weak signal.

Some of the best transistors for this kind of RF service are the VHF bipolars
that are used as cable drivers on cable TV systems.

-Chuck Harris