'70s EM-Arco caps same as '70s Sprague PS caps?

[David Root]

I pulled this out of another thread as it was OT. dreric had posted a website www.33audio.com that Tom had discovered earlier.

That website has some paper/polyester caps from the '70s, EM-Arco, of which the owner says :-

"They are very similar to the later solid-impregnant Sprague Black Beauty (later Di-Film version) and the Sprague type-PS Orange Drop that were also paper/polyester until the late 1970s. The EM-Arco and the Sprague Orange Drop appear to be identical inside. Perhaps Sprague made them all. Sprague had a trademark for their proprietary impregnant. EM-Arco did not state that they had their own impregnant."

Note especially the reference to PS orange drops that were also paper/polyester until the late '70s.

First, is it likely that HAD would have used these early orange drops? I recall Tony saying a while back that he did not think Black Beauty caps had any place in a Dumble circuit. When did HAD start using orange drops?

Secondly, does that statement have any credibility to those like Tony who have some experience with real Dumbles?

[67plexi]

NOS 1950-60s Sprague Black Beauty Di-Film are great for guitar tone caps.
I would be leery in a high voltage circuit due to leakage. The only reason to use an old Sprague BB
Would be for a restoration customer demand no warranty.

Steve.

[thyx]

The old Sprague caps hold up very well. The impregnation formula was very proprietary, and I wouldn't trust other caps by other companies of that era to hold up as well. The Blue Molded Fender caps being an exception. The only other cap that seems to hold up is...yep, you guessed it...the EM-Arco caps. Some speculate they were actually made by Sprague...which is something that happened often back then.

Additional note: If Dumble was using Sprague PS caps in the early 70's...guess what.

[Cliff Schecht]

NOS 1950-60s Sprague Black Beauty Di-Film are great for guitar tone caps.
I would be leery in a high voltage circuit due to leakage. The only reason to use an old Sprague BB
Would be for a restoration customer demand no warranty.

Steve.

The only caps (AFAIK) that actually say "Black Beauty" are the paper in wax unsealed caps that ARE dangerous to use. The big black (I think mylar) 160P/161P series aren't Black Beauties but are often called this I think because they are big, black and do sound great. I use 160/161P series stuff when I find it but that isn't often. I've never had one fail and honestly gave up on running any kind of out of circuit test (aside from value). If they look good and the leads are holding up, I'll throw 'em in a personal amp with no worries.


Is the indicator for paper in oil that little blob of solder right where the lead extends out of the body of the cap? I've noticed every PIO cap I use has this but also some of the vintage Sprague caps I've used are a plastic shell but have the solder blobs right outside of the casing. They don't have a series on them and they sure sound great to me..

[David Root]

This is what they look like. There are lots of caps that look like this in early Dumbles, reddish brown drops.

[Structo]

On this Sprague data sheet it has the Difilm® Black Beauty® Molded Tubulars
A dual dielectric of polyester film and paper.
Up to 1600 WVDC
Look at page 7.
http://www.33audio.com/enter/data/1972SpragueFilm.pdf


Also, I have said before but sometimes it gets blurred that Mylar is the Dupont trademark for polyester.
So Mylar film caps are indeed polyester.

Don't most NOS non electrolytic caps (film caps) have an indefinite shelf life?

From what I have read it seems that in the 70's or so polyester film caps were state of the art.
But, they have a poor temperature coefficient and are not stable when heated above a certain temp.

Then the polypropylene came along and proved to be more stable and had a lower tolerance shift.

But I guess that HAD thought the polyester caps sounded better in his amps so he used them.
Or was it because at the time they were the best thing going?

Anybody built an ODS amp using all polypropylene film caps?

[talbany]

Dave
I have not seen any Dumble amps using the caps in the picture you posted accept maybe 1 or 2 in spots here and there. I could be wrong and would love to see a picture of one using all these caps to prove me wrong.. The ones used in the earlier amps that I know of were the early brown ones labeled either Mallory's, CDE's or the GE's (I believe to be the ones in the Oddssey here)...
The ones above I've tried all have similar tonal qualities smooth velvety texture as the PS but are noticably darker and don't seem to have the open mid range like the PS's.. Still a very cool caps and like them very much..
FWIW...Early on I bought a bunch of those caps (EM's) in the picture you posted though they are not a bad cap they are not my fave...Put another way I still have a bunch of them..

Hope this Helps..

Tony

[David Root]

Thanx Tony, those are the caps I was thinking of.

So you are saying that the EM-DP caps in my picture should sound like the Mallorys, CDEs and GEs, but that they don't sound quite like the later Sprague PS caps?

[talbany]

Thanx Tony, those are the caps I was thinking of.

So you are saying that the EM-DP caps in my picture should sound like the Mallorys, CDEs and GEs, but that they don't sound quite like the later Sprague PS caps?

Dave
No I'm saying the Mallory's CDE's and GE's sound similar and the EM's sound different.. The GE's were most likely re-branded Mallory's since they sound identical to me..Don't know for sure..

Tony

[jelle]

I have used the EM caps and they sound really nice to me. In fact, they are in the one amp I got a lot of good comments on. Smoother sounding, not as pen midrange....OK, yeah, I see that.

[David Root]

I bought some last week. I'll try them out.