Cathode bypass caps

[jimiclow]

My Stereomour has been up and running. I temporarily installed a 330k carbon film resistor instead of the 259k that were missing (I have received the replacement from Eileen, thanks for the fast shipping). I'm very pleased with the sound, definitely more bass than my Zen or Taboo.
I built my Stereomour as a 45 amp. I have noticed that the PS resistors (1.2k) is running hot and I'm worried because they are very close to the cathode bypass and power supply caps. I have some Panasonic 105C 330uf 350-volt caps that I want to replace the 4-220uf caps. The 2 power supply caps are probably okay to replace but I'm not sure about the cathode bypass caps. Is there a disadvantage to using a larger value cathode bypass caps? I know my Zen uses a 1000uf cap even though a 47 or 100uf will do.
Thank you.

BTW, my Stereomour was upgraded using V-caps TFTF coupling and Mundorf 3.3uf SIO caps, Alps potentiometer, only 1 pair of input and no input selector.

 

[Grainger49]

Jim,

IIRC, and I'm old and might not have this right, you need to change the cathode resistor for a 45 output tube.  That sets the bias/current through the tube.  That, of course, changes the current in the power supply, with more heat from the PS resistor.  Better ventilation, raising the Stereomour on spikes, will help with this.

The cathode bypass cap is one of the most important caps for audio quality.  It is just behind coupling/parafeed caps.  It is considered in the audio circuit.  Bigger is good and a lower ESR is very good.  I know of no disadvantage of larger cathode bypass caps.

I would suggest adding a film cap in parallel with the bigger caps as well.  Try it with jumpers first to see.  I'll bet you solder them in.  Even a 1uF or 3.3uF will be an audible improvement.

 

[howardnair]

jim-grainger is correct- make sure of pages 13 --50- and 66 in the manual--as for the cathode bypass cap there was a thread a while back-larger value is good -size is a problem-film caps are better
thread is here
http://www.bottlehead.com/smf/index.php?topic=2024.0

  according to paul you can go comfortably  as low as 47uf -
i used the these mundorf films in the cathode bypass with a 47uf value@ 600v
in a 45 tube configuration-you can connect to the board or directly to the terminals via the schematic

http://www.partsconnexion.com/capacitor_film_mundorf_mtube.html

 

[jimiclow]

Thanks Grainger and Howard! ;D

Grainger, I did all the changes to my unit to run 45, although it's the 2a3 that I'm using right now because I only have one 45, waiting for another one to arrive tomorrow. I would look into adding a film cap to the bypass cap by paralleling it to the cathode resistor, maybe just 1% because of the size (3.3uf). I will try Obbligato or Auricap.

Howard, thanks for the link. I have some ASC 30/40, CSC 100 oil cans here but they're too big.

 

[Paul Joppa]

The 1200 ohm resistors will get hot - that's why they are bigger than the others. They function to drop the power supply voltage for the 45 tube.