JTM 45 and Caps

[Ed_Chambley]

My next amp build is going to be a JTM 45 and on Marshally sounding stuff I usually use Mallory's and sometimes Sozo's caps.  Orange drops seem to be bright.  It is probably just my imagination running away with me.
Doug sells Xicon caps and I bought some a while back just to add to my parts.  I have never used them.  Anyone ever used them in a Marshall build?  What are they most comparable to and where have any of you guys made use of them?  What was the outcome?

[jim]

I have a lost of difficulty telling them apart by sound. There is no doubt that they do color sound.   It is better to have higher quality coupling caps whereas lower quality (less expensive?) will do fine as bypass caps.  I would use as close to historically correct as possible
and that would be Mallory 150's or Sozo in the preamp.   I use Xicons for repairs all the time, especially PCB amps, because of their
radial orientation.   Jim

[tubeswell]

I've seen mustards on fleabay every now and again (altho' they are hideously priced, they are cool). If I was making another JTM45 for myself, I'd fork out for 'em just for the look.

[HotBluePlates]

... I usually use Mallory's and sometimes Sozo's caps.  Orange drops seem to be bright.  It is probably just my imagination running away with me.
...

There are more than one type of orange drop, but the most commonly seen type are 715P and 716P. These are polypropylene dielectric. EDIT: Forgot to mention there are also 225P polyester orange drops, which are smaller and do not have the brighter sound of the 715/716P orange drops.

The Mallory 150's (and probably Sozo's) are polyester dielectric.

In comparison, polypropylene is a more nearly perfect cap dielectric, which has lower losses and also requires a physically larger size for the same value. In many circuits, they will be audibly brighter. Only you can determine if that is appropriate for your particular circuit.

Polyester caps have slightly higher losses, and may seem to have slightly less treble. Some people interpret that as a "vintage sound." Again, only you can determine if you like that sound in your amp. The polyester dielectric allows the cap to be somewhat smaller for the same value.

Voltage rating impacts how far apart the plates of the cap must be, and therefore affects the size of the cap. If you compare sizes, be sure to compare caps with the same voltage rating. A 100v cap will be smaller than the same-value cap in a 630v rating.

Some caps are "metallized." This is where a plate is formed on the dielectric by sputtering molten metal onto it. The resulting cap is smaller than the same cap with the same dielectric and voltage rating in a film-and-foil construction.

I bring up size because the choice is often a matter of "will it fit?" Assuming the cap fits in your amp, try any/all of them to see if a different dielectric matters to you. My opinion is you will always hear a much greater tone change by changing a cap value than you will by changing dielectric type.

[Willabe]

I was reading at Aiken's site the other day and he likes the PP film/foil because they are more temp. stable than metallized film.

Can't say if that's true or not.     


            Brad         

[HotBluePlates]

I hadn't seen that on his site. Either way, temp stability might vary with each manufacturer and their product line. Best to consult the manufacturer's data sheet if it's an issue for you.

I can't say I've thought about an issue like that, except in test equipment.

[Willabe]

I hadn't seen that on his site.

It's in the Q&A section. He feels it will change the tone of the amp after longer periods of playing time.   


          Thanks,    Brad     

[The_Gaz]

Yeah, I know what Aiken's talking about. After I play for about 20 minutes I can hear this ringing coming from the polyester coupling caps. It's so loud, in fact, it sounds like it's coming from inside my head!