Older coupling caps

[Goodizzy]

Hello,

I have a pair of EMI STD/373 monoblocks which I am restoring. These are very high-end studio quality monitor amps with EL34s in push pull. I took two pictures of the EL34 coupling caps from both amps below. They read as follows-

(Black with red lettering)
Sprague
.47mf +_10%
600vdc
6tm-p47

(Green with black lettering)
Cornell Dubilier
Pm 6p47
600vdc
U.s.a. +_ 10%

From what I have read it seems some of those older spragues might be desirable? I am hesitant to keep them in, however, as both amps are running the original compliment of Mullard valves, including the EL34s! And i would hate to cause any damage to them. If anyone is familiar with these caps and their reliability or not, I'd be most greatful for insight. Thanks!

[Diabolical Artificer]

Those black ones are used in a lot of Tek scopes and HP scopes/ SA's. I've tested some and found some ok, some leaky. I'd replace them to be on the safe side with new caps from a known manufacturer, ain't worth the risk. BTW, test the new ones before fitting @ 10% over spec'd voltage.

"From what I have read it seems some of those older spragues might be desirable? " This is usually form the tube/cap sniffing brigade mostly based on subjective ideas. Buy new ones bung the old ones on ebay for $50 each with a description thus " Rare!!! Vintage!!! EL34/KT66/ 8551 Specially aged Sprague capacitor. Superior highs, mids, mellow sound " : ) I've seen several such descriptions, the breathless "Rare!!!" cracks me up.

Andy.

[Craig Sawyers]

This will make you laugh. Someone is remanufacturing the Spragues for the guitar market.

https://www.charlesguitars.co.uk/man...uty-capacitors

for £59 each. The world truly has gone bonkers.

[HamishBoxer]

What! 59 pounds for 2 caps? No good when changing them all in a Bush DAC90.

[G8HQP Dave]

Someone (Sozo?) is making 'mustard caps' too. I am unsure if it is the colour of the encapsulation or the slight non-linearity of the polyester dielectric which makes these so desirable in some audio quarters.

[ionburn]

Originally Posted by Craig Sawyers

This will make you laugh. Someone is remanufacturing the Spragues for the guitar market.

for £59 each. The world truly has gone bonkers.

And that was only the start, looking at their 'vintage' guitar pickups, which appear to be not really, just modified copies. At £268.00 a set of three it had me thinking, but on checking the current price of the humbuckers I bought years ago (now nearly £100 each) maybe not quite so bad there.

From what I have read it seems some of those older spragues might be desirable?

To a twit maybe, modern polyester capacitors a very good indeed.

[Goodizzy]

Thanks for the replies! I was leaning towards snake oil too hah.

[Craig Sawyers]

Originally Posted by HamishBoxer

What! 59 pounds for 2 caps? No good when changing them all in a Bush DAC90.

I have a CD player (a Tent labs, quite old). The DC blocking caps were Audio Note, copper can, paper in oil, (like the Spragues). Then a note came from Audio Note - the paper in oil caps were going (electrically) leaky, so please send them to us and get a polypropylene regular dielectric capacitor - in the same copper can.

This is a general rule - paper in oil caps go leaky, sooner or later. Hunts, of course, but also Siemens and Sprague. There may be others I cannot remember for the moment. One particular Hunts 0.1u was used in the Quad II power amp, and when it goes leaky it cooks the KT66 output tubes by taking the grid hard positive.

The corollary is - replace them on sight. If you want it to look original, with care you can hide a polypropylene or polyester tubular cap inside the hollowed out body. I did that with a Rohde & Schwartz SWOB II with leaky Siemens paper in oil - which were more like resistors than capacitors. The valve/tube bias conditions were all over the place until I replaced them.

Craig

[Craig Sawyers]

The horror, the horror. You can replace those caps with V-caps, for which a 0.47u, 600V will cost you $279.48 each https://www.vhaudio.com/v-cap.html

Or maybe not...

[HamishBoxer]

Good job the KT66's are cheap then! Not I add.

[Sideband]

If you want something really off the planet, round the bend or whatever you want to call it see here wooden capacitors

Must use rice paper......!

[Craig Sawyers]

[Boater Sam]

I'm for offering a rebuilding and reconditioning service for Sprague Capacitors.

Totally new, 40 year guarantee, indistinguishable from new. Fully burnt in.

£190 each, any value.

Carefully filled with sound stage powder and fairy dust.

No, I'm not joking, - honest.

[stevehertz]

Just change them. That passive components can be desirable is ridiculous. Change them and sell them.

[evingar]

Originally Posted by Sideband

If you want something really off the planet, round the bend or whatever you want to call it see here wooden capacitors

Must use rice paper......!

Jeeze the wheeze I despair, I really do. We appear to be heading back to the dark ages in terms of mumbo jumbo mysticism.


OK for playing Bach on though I guess - I'll get my coat

[gingpeakin]

There's one born every minute...

[ms660]

Wrong timbre.

Lawrence.

[Beardyman]

Oh my sweet Lord, I think that could be the modern equivalent of alchemy.
I really do despair sometimes, can people not see they are being fleeced?
I suppose if they know no better then they have no choice but believe what they are being told, but even so.........

[mark2collection]

Personally I'd seek modern replacements as close to original spec (value & physical size) as possible, and either reuse any labels (if at all possible) or, reproduce my own.

Not only does it look right, you have no fears about new-old-stock items damaging other parts.

The price of some of these items in previous posts, man-alive! If we followed this path it would make for an incredibly expensive hobby indeed, and would our sets sound any better?

I once saw a company supplying audio grade fuses for the mains plug, £65 a go! EDIT:- They've come down in price since 2006, now only £24.95 http://www.analogueseduction.net/cat...a-uk-fuse.html

Some of the worlds best recordings were done on equipment which never had audio grade parts, oxygen free DIRECTIONAL wire (for an AC signal ) or anything like that, it was all down to engineering practices both equipment & recording technique.

In all honesty, modern caps will most likely meet or exceed the originals in terms of stability & life anyway. Manufacturing techniques have improved & we no longer have the post-war constraints in acquiring materials.

Replace the caps, use modern off the shelf items (Vishay are very good, usually a bag of 5 items comes in at less than £5) & reproduce your own sleeve/labels.

Mark