Question About Capacitor Upgrade in Tube Amp


I am preparing to do a coupling capacitor upgrade on a recently purchased tube integrated amp. The two 0.22uF on the preamp tubes are fairly straight forward. But I noticed another similar model 0.33uF cap on the large filter capacitor for the B+ supply that is installed across the hot lead to ground.

Does this cap on the B+ just block high frequency noise from the power supply or does it have any effect on the amp tone? Is there any reason to "upgrade" this cap?

I know it may be hard to tell exactly what is going on without a schematic.

Also any recommendations on a good cap to use in the upgrade of the coupling caps? I was looking at Mundorf SilverGoldOil for the quality at not too crazy a price. The amp already sounds good but lacks a little clarity that I think a coupling cap swap will help with. It is SET 300B amp.

Thank you!




I am going to respectfully disagree with the above comment that disparages upgrading your amplifier’s coupling capacitors. Tube amplifiers in general and particularly SET amplifiers have very straightforward/simple circuit layouts. With regard to the SET amplifier there is a lower part count.

Essentially one could argue that because of this, each part individually takes on more importance particularly in the audio signal path. I believe that changing to a higher quality coupling capacitor is a very good idea and money well spent. 

if you take the time to research and do further reading/investigation you will find a better capacitor that will contribute to improved sound quality. I’ve had splendid success with the Duelund CAST copper foils. Considerations are available space for a given capacitor and the cost. No doubt there are other excellent choices available.

I suggest that you reach out to @grannyring via site email. He is most definitely a knowledgeable and helpful resource.


I have inexpensive Jantzen (2.2) red colored caps in my Bottlehead Paramours that sound excellent.

Been thinking about going SS, but if I don't I may try the Jantzen silver colored caps which are said to have a bit more detail.

I don't recall what was in their originally (been using them for 20 years now).

I looked @ Audyn  copper when they first came out, but 2 of them cost twice as much as I paid for the amps/mono-blocks.

However, if you go with Zipost's advice don't stop there as you can also downgrade your speakers, cables, source gear and maybe even the tubes if you are lucky.



Bottlehead is a good example for illustration. They are inexpensive and thus a low barrier of entry for budget buyers. Although low cost, they are consistently well designed and engineered. They are good candidates for upgrading to better quality parts due to their solid engineered foundation. They will definitely respond to higher quality capacitors/resistors/transformers/tubes etc.


Thanks for the replies so far.

Did anyone know if the .33uF on the B+ filter cap is just for noise filtering on the power supply or does it have any effect on the amp sound? I probably will just leave that one alone unless someone one here has some advice for that one.

I will check out those other caps mentioned.