Bright cap replacement?

jack daniels · Post by **jack daniels** » Wed Dec 19, 2007 5:34 pm

Wow, its hard to do a Search for Bright Cap values on this board. A million posts have the word "cap" in them. LOL!

I have a 77 50 watt JMP non- master. It was so darn bright that it was almost unusable. I lifted one leg of the bright cap on the volume pot. Huge difference. At low volumes it sounds awesome! But I almost find that it lost some of its grind, saturation and chime. What is a reasonable replacment cap for this position? I want it to be much fuller at lower volume, but still have some chime on top, which appears to help the Greenbacks saturate and compress....

I think the original was a .002 ceramic disc. Can I use something like an orange drop .022? I have a few from my Les Pauls tone caps. Would a ceramic cap be more appropriate or can I substitute the type of cap? I have a lot of caps left over from when I was building Mic Pres and Compressors for the studio. I must have something that will work.

What did the late 60's Plexi's have?

Thanks and sorry I couldn't find anything with the search.

Billy Batz · Post by **Billy Batz** » Wed Dec 19, 2007 6:00 pm

You can try all different values. .022 is a huge value for that position. I have actually tried that with good results in some ways but the volume control is completewly useless. It would go off-on-really on. No control really. The brite cap allows frequencies to bypass the pots resistance freely so it has more of an effect when turned down and is shorted at full volume. 500p is a value often told to use when an amp is too bright but I really think 500p is brighter in a lot of ways. It doesn 'boost' any more or less then a 5000p (5n) which is a high value, it just boosts different frequencies. 500p allows only highs while 5000p allows mids which gives it a touch more body in some ways. So I wouldnt suggest just changing the value of the cap but put a resistance in series with the cap itself to reduce its effects. Try different values for that resistor as well. Say from 100k-500k.

ODs arent looked highly upon around here but you can try it out. Try different things but the most common here are silver mica and ceramic.

bartak · Post by **bartak** » Wed Dec 19, 2007 6:11 pm

You have an awesome amp there, before you start messing with that beauty you should consider changing the pickups in your guitar, or just the tone cap in the guitar can make a huge difference, also different speakers can make a huge difference.
I'm not sure why so many people want to mod there vintage amps. I would never do it, I would buy a different amp first. I know it's just the bright cap and thats not a big deal but I've owned a lot of vintage amps and have never felt that any of them needed to be modified. I hope I don't sound like a jerk It's just my 2cents

jack daniels · Post by **jack daniels** » Wed Dec 19, 2007 10:39 pm

Thanks for the tips. Actually, the amp is a killer combo. My speakers are the original Greenback, but I have tried my tone tubby's, Weber Cali's, Pyle Drivers like Derek Trucks, a Marshall 4x12 with G12-75, a Marshall Heritage and about 4 or 5 other cabs. The results are the same, to bright unless vol on 8. My guitars, well I own about 10 Les Pauls from just about every decade. PAF's, Pre-T tops, T-tops, B Buckers, 57 classics, 490/496 and at least two Symour Duncan equiped pauls. I don't think it is the guitars or pickups either. It just the nature of the amp.

I have considered selling/trading the amp. But I would need to get into something earlier like a plexi from late 60's or early 70's where the right value components were still used. Otherwise a bogner Shiva is next.

JD

rockstah · Post by **rockstah** » Thu Dec 20, 2007 4:22 am

if yours was a 2000pf cap try a 1000pf bright cap.
http://thetubestore.com/ca-si-1000pf-500v.html

jack daniels · Post by **jack daniels** » Thu Dec 20, 2007 10:05 am

Thanks for the tips! I do think I have 1000pf caps in my drawer. I may check this out.....

toner · Post by **toner** » Thu Dec 20, 2007 12:49 pm

I would get several silver mica caps and alligator clip them in so you can quickly try several values at different volume settings. Don't hesitate to try smaller caps too (47pF - 250pF).

Otherwise, Dan's suggestion below about putting a resistor in series with the cap is definitely worth trying. You may find that a large bright cap (1000pF +) with a resistor sounds good to you.

Billy Batz wrote:...So I wouldnt suggest just changing the value of the cap but put a resistance in series with the cap itself to reduce its effects. Try different values for that resistor as well. Say from 100k-500k.