Tube Amps / Music Electronics
For current discussions, please visit Music Electronics Forum. New: view Recent Searches.
New: visit Schematic Hell!
The sunn still shines online!

Listen to great tunes streaming live right now!

ampage archive

Vintage threads from the first ten years

Search for:  Mode:  

Dumb capacitor question?

11/9/1998 2:01 PM
Benjamin Fargen
Dumb capacitor question?
Can you tell me the correct replacement value in relation to the value between older caps and modern caps?  
.0005? what is the correct replacement?  
.02 ? is it .022  
.005 ? is it .0047  
This is a dumb one, but I just wanted to double check!  
Thanks, Benjamin
11/9/1998 2:28 PM
Jim S.

Most capacitors these days are available in "decade" values, just like resitors. For 10% tolerance components, the values will be any one of {1, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2} multiplied by 10 raised to some power. This scheme allows a component having ANY measured value to be labeled with the nearest decade value and still be properly within 10% tolerance.  
Assuming the values you listed are all in microfarads (uF), the closest decade value to .0005uF (which equals 500pF) is 470pF. However, 500pF ceramic and silver mica caps are still commonly being manufactured, so you have a choice.  
In general, I would say "correct" is in the ear of the beholder. It's extremely difficult to distinguish between a .02 and a .022 cap or a .047 and a .05 in a guitar amp. I find that changing a single cap's value by much less than 50% up or down doesn't affect the tone dramatically. If I'm restoring a very old amp I might want to stick with the non-decade values for general reasons of "correct vintage specs", but usually I don't sweat it if I need to replace a .003 cap with a .0033.  
Non-decade value film caps are also still being manufactured, but they are harder to find. The SBE (formerly Sprague) 6PS series orange drops are available in the older non-decade values such as .02uF, .025uF, .03uF, .05uf, etc.
Book Of The Day The Ultimate Tone, Volume III by Kevin O'Connor
Have you ever wondered if there is a better way to build a Bassman, Champ, Plexi, an 800, AC-30, Bulldog or Portaflex? Or you wanted to build an SVT with off-the-shelf parts? How about a master-volume amp that doesn’t change tone with the master setting? Everything you need to know is right here, including: proper grounding techniques, wiring methods, and mechanical considerations. Eighteen chapters cover the “iconic” amps everyone knows and loves, with schematics and layouts for each, along with the technical history of the product. Eyelet-board and chassis-mounted tube socket construction is used throughout, for easy servicing and modding. TUT3 is very accessible even if you cannot fully read a schematic and is a "must have" if you are going to build an amp for your self.

Note: The Ampage Archive is an Amazon Associate site. A small commission is paid to the site owner on any qualified purchase made after clicking an associate link such as the one above.
11/9/1998 3:09 PM
Benjamin Fargen

Jim, Thanks so much for the help! Do you prefer ceramic or silver mica caps for the 500pf?.... or can you even tell them apart?  
11/9/1998 5:31 PM
Jim S.

Generally, I will upgrade to silver mica. Silver mica might be slightly less grainy sounding, but I don't think there's that much difference for guitar amp use. I doubt anyone could tell the difference in the case of the 500p coupling cap used for bleeding off the reverb drive signal in Fender amps.
   Page 1 of 1