Bottlehead Forum

Bottlehead Kits => Mainline => Topic started by: hpleung on January 03, 2022, 06:43:58 PM

Title: Question about those little capacitors 0.1Î¼F 100V
Post by: hpleung on January 03, 2022, 06:43:58 PM: Hi,

I was curious regarding those little yellow capacitors - it is so hard to solder them and working on so tiny space. One question I have is - what if I use wires and instead of soldering the tiny capacitor close to the tube mount as describe, I just solder them outside - say a few millimeters outside of the tube mount. Do they need to be so close to the tube mount?

Thanks.
Title: Re: Question about those little capacitors 0.1Î¼F 100V
Post by: Paul Birkeland on January 03, 2022, 06:49:01 PM: Can you post a picture of what you're thinking of doing?
Title: Re: Question about those little capacitors 0.1Î¼F 100V
Post by: Paul Joppa on January 04, 2022, 04:49:20 AM: A little technical background, for those interested:

Those caps are mounted that way for a reason. Tubes with high transconductance (and the 6C45 has a very high transconductance) are prone to oscillate at very high frequency, often in the hundreds of megahertz. Such oscillations can be subtle and are extremely difficult to diagnose, so several precautions are usually taken to reduce the probability of that happening. The caps, and their location, are among those precautions. The design takes as many precautions as we thought practical, balancing difficulty of construction against likelihood of a problem. It's a "suspenders and belt" approach - probably overkill but better safe than sorry.
Title: Re: Question about those little capacitors 0.1Î¼F 100V
Post by: hpleung on January 04, 2022, 06:00:19 AM: Thank you to both of you. The info from Paul Joppa was what I was looking for - that is, there is a reason for the way it is mounted - which to a novice like me, looks like a strange location. The space there is so tight - i am not sure if i touched the capacitor with the solder pen. My mainline is sounding fantastic BTW - but I am always wondering if it could sound "fantastic + 1" if I did better job with the soldering at that location.

I may decide to redo that area with a replacement capacitor. I will post a picture if I end up doing it. Thanks.
Title: Re: Question about those little capacitors 0.1Î¼F 100V
Post by: Paul Birkeland on January 04, 2022, 06:32:09 AM: If the amp is running properly and those caps are all installed, I wouldn't be too worried about it!