The "black beauty"capacitor phenomenon...

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cfz2882

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cruising around some of the vintage electronics forums,seems these 1950s era capacitors have long had a bad reputation for becoming unstable and lossy as they can absorb moisture despite the molded baklite casing.As problematic as these capacitors are reputed to be,they are highly prized by the guitar amp guys for the tonal characteristics they recon these capacitors have-even saying they have to be "broken in"with some usage before they sound "right" :) NOS and even salvaged "black beauties" can be found on Ebay.These are paper dielectric with molded case.
 
Interesting.  Everything I've ever read about black beauties has described them as problematic and suggests they're the first place to look if there's trouble. 
 
indeed

next time I have any of my 40s/50s electronics apart,i will look out for any bumblebees or black beautys :)I know I have some in my spares stash-will have to do some tests on those to see what happens.
 
I've got perfect pitch

And I have to say - to my great regret, that the black beauty bombs do contribute to the sound.

Sadly, because their leakage also contributes to overheated plates and early tube death.

They explode, they catch on fire, they leak, yech.

Bumblebees should be replaced ruthlessly and without exception. They were trash when new.
 
Yes,I replaced caps like those in older amplifiers-Hi-Fi or G-Fiddle when they were old and leaky.Never had any of those explode-that is electrolytics and large oil filled caps that explode when faulted or shorted.The black caps were coupling caps-coupled the plate of one stage to the grid of the next.And yes the tell tale plate glowing of the output stage when the coupler caps get leaky-passing DC and putting a "false" bias on the next stage.In those cases-doesn't matter what kind or brand the coupler cap is-REPLACE IT!!Often have small oil filled couplers in AM transmitter modulator stages-same problems.Those couplers could have to block up to 6Kv!Have replaced the couplers in my "MAC" amps-but no HV caps available of the power supplies.While you are replacing the coupler caps-you may and should replace the bias rectifier diode as well.Often in those older electronics the bias diodes were selenium-these get weaker as they age-output voltage gets too low to properly bias the output stage.Do this as well when redoing older amps.
 
Rex,

You are so right - selenium used for any purpose is dangerous at this point. Just have to adjust for the different voltage drop between the nasty old and safer new diodes.

 

I've caused electrolytics to explode by putting them in the wrong 'way round. Sure I'm the only one to ever do so. 
 
While working in one of our transmitters today-we replaced a pulse step modulator module in our BBC 500Kw transmitter.PSM modulators are solid state-they use a triac like device-a GTO this handles 900V-1800V Pk at up to 60A.There are 32 of these modules in series to provide DC to the plate of the PA tube and modulation to it.The GTO is controlled by a circuit board-the board has a +- 15V supplies-the caps in this module were blown to bits-foil and fluff all over the board.So we figure both legs of the supply are trashed.The board is powered by a special step down transformer that takes 650VAC to 24V center tapped for the board supply.Now these moduls float at 12Kv above ground.The GTO device is powered by the secondary winding of the HV transformer-3Ph 650V.There are two transformers-16 isolated 3Ph windings on each.4160V 3Ph primary.Besids the PSM module there is a rectifier module for each mod module.3 fuses protect the rectifier boards.When those blow you check the diodes and surge diodes.If bad-replace them-then the 63A 700V fuses.Right now 3 of the modules oscillate-isolated them by pulling their fiber optic couples from the modulator driver boards.We have to rebuild the bad boards we pulled.Replace the GTO is the irst thing-they usually short.And those things are like $600 each!At this point like PP high level plate tubed modulators better!not so complex-less to blow.And the trouble above mainly caused by two 1000Uf 25VDC electrolytic caps!We are wondering the fun when the 3300 UF 350 VDC main filter caps in the rectifier boards go!They are 30 yrs old !!!Have strongly recommended these be replaced.I forget how many are in the transmitter-LOTS!!!!!!!
A charging circuit is in the rectifier board to limit current when the HV transformers are energized.Then a contactor bypasses the charging resistors.In some other transmitters I have worked on they had selenium rectifiers for the PA and mod bias stages.The transformers for these were multitapped to compensate for rectifier aging.Simply replaced the old selenium diodes with silicone ones-added like a 400 ohm surge resistor is series with the new diodes.Works much better!!!RCA "H" AM transmitters-5,10Kw.
 
Indeed the old vintage components can and do have a different sound to them, the dialectric absorption isn't as well controlled as with modern parts so they are apt to cause their own distortions. It all depends on if said distortions are good or bad. We all likes what we likes in the end.

I'm a hifi fan, I believe in accuracy to the source and anything I can measure that is causing degradation has to go. I replace all the old coupling and bypass capacitors out of habit, modern plastic film capacitors are just better and more reliable. To a degree any amplifier I have worked on is "restomodded" even if just by the substitution of newer superior parts.

To a degree as soon as I hear people start talking about electronics "breaking in", I generally take such comments as crossing the line into psychoacoustic. In other words it is amazing what the mind can imagine. Breaking in cables or worrying if speaker cables lie on the floor vs being propped up on cute little stands. A lot of it comes down to the power of suggestion, if you think it makes a difference then when you listen it will. Boutique parts fall under this category, Audio specific capacitors that cost 100x more then similar commercial parts are just silly, but I suppose if you know they are in there then you will think it sounds better.

Guess I should start clipping out the Black Beauties with lots of lead length and put them out on eBay. My 1980 Marshall 2204 guitar amp still has all its original capacitors (course they are far more modern then Black Beauties) so I haven't messed with it. Well other then ditching the 6550 output tubes in favor of EL34's. I just didn't fancy the way the more modern HiFi tubes overloaded.
 
Many a tube has red-plated...

due to old leaky Bumblebees, always replace them. As to selenium rectifiers, in non-tube rectified electronics we always replace selenium with a 1N4007 silicon bridge, and as those give too much voltage add a 47 ohm 5 w resistor between the silicon bridge and the filter cap to drop the voltage to acceptable levels.

In the early 2000s we at VTV magazine did very extensive double blind testing with some notable engineers, designers, restorers, collectors &c in the Bay area of vintage HiFi and guitar amps with various and sundry types of caps for vintage HiFi and guitar tube amps. Conclusion: cheap Illinois metallized polystyrene jobs sounded every bit as good in vintage amps as "boutique" Auricaps and that expensive ilk. That's all we use in restoring any tube amp; we have H-K and Heathkit stereo tube units sitting on the bench as we speak.

The guitar guys can have their silly Bumblebees, they're the very same idiots that drove up prices of certain tubes to absolutely absurd levels. We sold them all our overpriced Telefunken and Mullards long ago, the old RCA, GE, and Sylvanias work just fine.
The audio snake oil salesmen are alive and well!
 
The Hi end Hi-Fi "Audiophools" are also responsible for the high prices on tubes and tubed amps.We can't put all the blame on the G-Fiddle guys.For some of those folks on both sides--I have a bridge for sale REAL cheap!!!Now the thing among audiophools is you must have a separate powerline feed for your system and premium grade outlets!
 
I have a high end Hi-Fi catalog that shows speaker cable supports-----Al they are are simply porcelion powerline insulators---just get friendly with any lineman-you may get some of those for free!Maybe the Hi-Fi guys should erect utility poles in their Hi-Fi room with crossarms and insulators!Oh No I am giving them ideas!You might see utility poles shown in that catalog!!!There was a video on YouTube or something that showed a Japanese Hi-Fi guy paying for a separate utility feed for his Hi-Fi equipment room-even with its own pole and "pole pig"!His wife insisted she couldn't hear any diffrences-but he insisted that he could!
 
I believe that the only reason black beauty capacitors sound different is because they're leaky. A nice new Cornell Dubilier (formerly Sprague) "orange drop" capacitor will put the equipment back to factory sound and spec, no matter if it's in the amp on on the tone control inside the guitar. No need for expensive "boutique" capacitors, the only thing they're better at is draining your wallet.
 
the current world vacuum tube market

Right before he died Charlie K, publisher of VTV, did an exhaustive analysis of the state of the worldwide vacuum tube market, at that time about $50 million/yr in revenues, now close to $100 million. It was never published as the last issue, though it was in the can, (and I had done the editing, and had an article about Grommes/Precsion in it, and had even been paid for it), never made it to press, as he died the next month, however he had sent me a copy of his analysis. Vacuum tube production now is almost entirely Russia (Sovtek, ElectoHarmonix), China (Shuguang, Liuzhou) , some Eastern Europe (JJ), with tiny miniscule US production (Richardson) for a few esoteric military and broadcast types and hyper-expensive radio/audio types such as 300B types (Westrex under WE patents).

The guitar market in 2016 constitutes approx 90% of the total world market of new tube production by revenue, and the production and re-introduction of almost all current guitar/radio/audio types is virtually completely supported and financed by guitar mfr'rs such as Fender, Marshall, Guitar Center &c. New Sensor (Mike Matthews) bought the old Reflektor Saratov (USSR) plant in mid 2000s, a guy I know used to be the US Svetlana Chief tube engineer, and Matthews/Sovtek/EH now produces new tubes there under the Sovtek and Electro-Harmonix name as well many legacy names such as Genelex, Mullard, Tung Sol, Bugle Boy etc. and OEMs to Ruby and other big guitar suppliers. World 12AX7 production ALONE exceeds 700,000 units/ yr.

If it hadn't been for guitar demand, new production of all of these tubes would never had happened. While a few of the, mostly Asian, radio/audio crazies, and I have sold much to them, have forced a few tube types such 300b, 2A3, 45 and that ilk to new heights, the VAST majority of upward price escalation of desirable vintage tubes has been due to guitar gurus paying totally insane prices for once common and now in great demand tubes such black plate RCA 6L6GC, TS-6550, Tele 12AX7, Sylvania 6V6GT, Mullard metal base EL-34, Amperex Bugle Boy EL-84, &c to get that vital (in their mind) crunch or twang whatever, as guitars control even more of the vintage tube market than new. Go to tubeworld.com and other vintage tube dealers to see just who they are marketing to.

So while the antique radio &c types like to talk about the "audiophool" effect, in reality its the guitar market that TOTALLY controls the market and prices. Now that CRT production has virtually disappeared, there would be no NEW tubes but for guitars, so we can all be thankful for that, while the audio, plus vital broadcast/radar/military, markets are less than 10%. However the other side of the coin is that it is also guitar players who have driven desirable vintage tube prices into the stratoshpere. Win some, lose some, good thing that I already have my lifetime supply, as I could never buy them now.
 
How about we step back a moment and look at the flip side. Imagine that there is no guitar market. All the reproduction and reissue new tube production would be less likely as the demand would be lower. All those desirable NOS tubes of old would command yet higher prices then they do today. And that would be just for the hifi demand since they could be the only available tubes.

Perhaps we should be thanking the musician world for lowering tube prices on the whole by making them available again? The guitar amp world is really where tubes make the most sense since they generally run them in the non-linear region which is where tubes really have an advantage. Run in a linear manner in a well designed circuit, tubes and solid state are generally indistinguishable from one another. I contend the 'warmth' associated with tubes is due to psychology from the look and feel (and smell?) of them coupled with the agreeable distortions of transformer speaker coupling.
 
I think it's also worth noting with the home audio market that in some ways prices have actually dropped on tube amplifiers. At one time, there was no such thing as a cheap tube amp. They all cost $$$$, and I even recall seeing articles saying cheap tube amps weren't possible. (Output transformer costs were always a major issue.) But, thanks to China, we now have tube amps that are cheaper than, say, 30 years ago--and when one adjusts for inflation, the prices are really cheap vs. 30 years ago.

 

Of course, the question does come up how good those Chinese amps are... But they do appear to be a viable alternative to a budget solid state amp. The two complaints I've heard are poor sounding stock tubes (but that's easily fixed by buying better tubes), and possible power issues (which may or may not be a problem depending on the speakers, the room, and the expectations/hopes/dreams of the buyer).
 
I did indeed note...

in (paragraphs 3 & 4) that we have the guitar market to thank for production of most, if not all, tube re-issues and the continued production of new tubes. As I said there it's the flip side of the coin, current genuine vintage tube prices being the other.

Why care? The chief problem as that genuine premium NOS tubes, in general, are superior to new production for a variety of reasons: from scarcity or current unavailability of super-expensive reagent grade strategic metals for cathodes, high purity nickels, readily available at the height of the cold war, the quality of vacuum hardness due to adequate time not being taken to evacuate as much due to cost, to variability of grid spacing due to lack of ultra-precision equipment in the US and W Europe, most of which was scrapped at the end of the post-war tube area, now having to be re-created in China &c without that legacy knowledge base, and general lack of QC. East Bloc and China mfr'ers are now making tubes in batches of 10,000 at a time with emphasis being on numbers, not quality, as folks don't want to pay $100+ for a new 12AX7, but guitar guys WILL pay that for genuine original Telefunken Smooth Plates, I sold 60 of them last year to a guitar sales & repair outfit. The quality control, burn-in time, materials expected in 1960 is just not present today.

As to sound of SS vs tube, it's primarily due to the well known audio phenomenon, described in great detail in a back issue of IEEE magazine, of the way even-order 2nd and 4th order distortion harmonics prevalent in vacuum tubes are perceived by the ear & brain vs the prevalence of dry and harsher sounding odd order 1st and 3rd order distortion products which predominate in transistor produced waveforms, something easily observed by instrumentation as well. Also large amounts of feedback generally applied to SS circuits to reduce distortion and improve bias stability is detrimental, as are a number of other issues to do with types of caps that can be used in low vs high impedence designs, &c &c. Bottom line: we got rid of all our tube audio stuff in the 1970s for TOL SS stuff but quickly lived to regret it. We sure don't subscribe to all the silly line cord, wire, foam pyramids, stone feet &c other loonieness &c but we sure do hear the sweet sound of tubes. YYMV.
 
Every time I see a discussion about capacitors, I think about the 1950 Plymouth tube radio I restored about 20 years ago.

 

It wasn't working, you see. I set  up a six volt car battery on my dining room table, took apart the radio, and replaced all the tubes, the "vibrator" (a gizmo for turning six volt pos ground into higher voltage for the radio), and as a matter of course, I assumed ALL the capacitors had gone bad so I replaced ALL of them. Oh, and the speaker too, and I fixed the little pointer on the station indicator.

 

The end result was that the radio worked, but the volume was low. I could never figure out why.

 

Then after the Internet matured a bit more, I was able to figure out where I had gone wrong. I had correctly interpreted the values on the various cylindrical capacitors. But the little square ceramic ones sort of  threw me. Finally I decided, at the time, that they had the same color coding scheme as the more familiar carbon based ones. Turn out they have a different format, and I was likely off by at least a factor of 10. Which way? Which ones? Got me. I think I tossed all the old ones and didn't record their old positions. My best bet would be to locate another 50 Plymouth radio, open it up, and inspect for the square ceramic capacitor locations, record their color codes, and then figure out which ones on my car radio need to be fixed.

 

OK, that's my capacitor story. Your mileage may vary.

 
 
'50 plymouth radio

might be a schematic such as Sams that will give the proper values for the caps to get that Plymouth radio working proper again :)I haven't had too many capacitor incidents worth reporting-on my '62 Stromberg Carlson school PA tuner,and '81 RCA garage TV,bad filter caps were immediately obvious :) the 2004 home PC and the 2010 vmw cabrio washer took a little figuring to conclude those needed recapped! junk Chinese capacitors that expired waay early were the cause of both those devices becoming inop.Have had a couple selenium stinkfest incidents though:1 st was when I took apart a small 1960s SS phono,then decided to use the amp-hooking the poer wires direct to cord instead of off low volt aux winding on motor :)About 12 at the time,noticed a tiny epoxy encapsulated rectifier had blown up,but didn't know what selenium rectifier was.2nd was when I included a selenium bridge rectifier into a project powered by 115 v and didn't know they only handle ~30v per plate-powered up the device and the rectifier held for about 1.5 seconds before it let go under the chassis spewing gawd-awful rotten egg smelling red smoke and fouled the underchassis area with reddish smoke deposits :)
Back to capacitors,poking around some Studor-Revox forums,discovered the "Frako" capacitors found in a lot of German and some other European equipment is supposed to be extremely suspect and I have Frakos all over the place in my german and Tandberg home audio,old Blaupunkt car stereo gear,VDO gauges,even my Porsche 928 :) Hardly any trouble with any of this except some very small Frakos where the rubber bung had shrank and cracked with age and caps went bad-could not find correct replacements,so had to remote mount a larger size cap and string wires so my Blaupunkt cassette would work again :)
 
graceful clipping versus hard

We've all covered this territory many times. In the end, it's easier to get first class, low distortion out of tubes than transistors. That doesn't mean one can not, but it takes really good logic control to do it.

 
 

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