• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Additional MKP/MKS Bypass on already present Cathode Bypass Electrolytic Capacitor for better Sound ?

Both in power and line/phono-RIAA pre amplifier stages are often to find capacitors between cathode and GND.
Unfortunately the various threads under
https://www.diyaudio.com/community/threads/choosing-cathode-bypass-capacitor.255366/
https://www.diyaudio.com/community/threads/cathode-bypass-capacitor.233663/
https://www.diyaudio.com/community/threads/cathode-bypass-cap-vs-no-bypass-cap.254781/
https://www.diyaudio.com/community/threads/help-understanding-cathode-bypass-capacitor.396622/
http://www.nutshellhifi.com/library/FindingCG.html
discuss the cathode bypass capacitor as a whole part, while I am interested in which type of film capacitor is best suited for parallel connection to the present electrolytic cap when space is limited.
In commercial tube amp components sometimes are to find MKT/MKS, MKP or nothing on this point - and this is the reason to start this thread.
Thank you very much for some hints so as related URL's.

P.S.: concerning the RIAA amp device in post #31 - go to
https://www.diyaudio.com/community/threads/schematic-wanted-for-vtl-preamp-maximal.158725/page-2
rises up the question, whether one decide on an MKS/MKT version with a higher value or with the same size for a lower value - but then with the higher-quality - i.e. MKP/FKP version (due the low voltage condition on that point a 63VDC version is enough).
 
Purchase the non electrolytic bypass cap of your choice.
Install the cap across the Left channel electrolytic cap.

Build a switch, to switch both:
The Left channel output from your CD player (or Vinyl setup): to the amplifier's Left channel input, and the Right channel input
Switch One loudspeaker from the Left channel output, to the Right channel output (a single DPDT switch switches input and output simultaneously).
For many amplifiers, you need a 4P DT switch, so both amplifiers are always loaded (with a loudspeaker, and 8 Ohm resistor, or just the two loudspeakers; do not chance ruining a channel that does not have a signal in, but does not have a load of some type at all times)
Switch back and forth, back and forth. Listen.

Now, invite your local audio club members, and invite them to listen to the modified Left channel, and the un-modified Right channel.
Say nothing to the listeners except that they need to listen for a difference, and to describe the difference in the music.
That is a fairly well done, not perfect, double blindfold test.

If nobody can statistically hear the difference, or describe the difference, you know how to save your money.

I am guessing that the more dB of negative feedback, including local, and global, the less the extra capacitor will affect the sound.

Just my opinion and experience

YMMV

Have Fun!
 
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This is a good description in general when it comes to finding out whether the sound signature is actually changing or not, but no satisfactory answer to the question in post #1
Under
http://aeaaudio.com/audiophile-quality-capacitors-going-beyond-the-simple-re-cap/
I read follow:
There’s one other critical place for this bypass treatment that is almost always overlooked – the output stage cathode bypass capacitors.
Electrolytics used for cathode bypass must be replaced or bypassed with good quality polyethylene types for the best sound—even though they can be rather expensive. Very few amp restorations, or even newly designed tube amps for that matter, take this critical step to improve performance.

According this the question under "P.S." in post #1 is answered.
An other option seems to be use of a low voltage tantal electrolytic cap - go to Hiraga's approach under
https://www.bonavolta.ch/hobby/en/audio/hiraga.htm
1.18, (pg 25) under
https://www.valvewizard.co.uk/Common_Gain_Stage.pdf
show in fig. 1.26 the frequency response of the cathode bypass.
 
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