Roederstein 'BAKELITE' series EK capacitors - "Living Legend" OR "Looney Legacy" ...?

[The Space Egg Corp]

Hi cap cruncher's !


Just wondered if anyone has ANYTHING at all, to say about these ?

I searched around a bit on the wonderfull WWW...
...but turned up...not much.

I believe they were used in Quad 22's for example...
...and I think Naim Audio used them for sensitive de-coupling duties.

Very old Bakelite has somewhat of a reputation for simply disintegrating & falling apart.
At best not much long term ( we are talking DECADES here ! ) dimensional stability.
However, I believe later, perhaps slightly post WWII Bakelite, was a bit improved.

It seems that the Roederstein EK series, was produced long AFTER other plastics & materials as alternatives, were available.
Also, why not just bung the cap in a 'tin can' like everybody else ?

It's seems to be an early version of the now common 'audio electrolytic'...
...obviously sonic issues addressed in the design ?

Is it 'low impedance' ? ( haven't got a clue ).
Does it 'sound good' ? ( dunno mate ).
Did you pull 'em out of your Naim gear, & reach Nirvana ?
Did you pull 'em out of your Quad gear, & wish you never had ?
Anyone using 'em for phono-pre's ?
Anyone think they're only fit for the dustbin...
...or have their stash in a bank vault ?

Love to know any members loves, hates, anecdotes etc...

..." Tales Of The Legendary ROE Cap"

Cheers.

Si.

PS...if you tap 'em with something, they seem VERY non resonant, compared to say, Nichicon MUSE...
...pretty scientific, huh ?

[Elvee]

I have tested them, along with many other types, old and young.

I am unable to find the thread, I don't even know if I posted the results on DIYaudio.

Anyway, I remember they were excellent, capable of competing with more modern types on all aspects, except the size/capacitance ratio.

Other than that, they are of exceptional quality, and also remarkably durable since the samples I had were at the very least 25 years old, some much older than that.

Siemens also made very comparable caps, both in construction and quality.
They also had an identical form factor (probably resulting from some old DIN standard).
The only difference was the color: bright orange instead of dull brick. But the quality was very comparable. It was the GSF series.

I'll try to make some fresh measurements on both types and post the results.

[Preamp]

Those are the ones that I used to replace in almost every defective Grundig TV set that I had in the workshop. They all ran out of capacity and dried out, some of them even cracked up. Maybe that was only due to lots of heat in narrow power supply sections, but since then I don't like them very much .

[The Space Egg Corp]

Hi Elvee
Yes...Interesting...I have seen ( but not used ) the Siemens GSF orange ones as well.

Hi Preamp
Yes indeed...I heard they did not fare too good in hot environments...Quad 22's were an example.
Haven't seen bad reports from 'cooler' Naim Audio preamp environments though.
Perhaps they prefer, say 20v duties for a 40v cap ( bit underated ? ).

So...not sure there was any great 'audio advantage' in a Grundig TV set...
...I wonder why they used the EK's as opposed to regular 'metal cans' ?

Had wondered if it was a 'can insulation' issue...
...but I've not seen an EK series cap that is over 40v rated.
Did they come in much higher voltage ratings ?
Anyone know ?

I think Quad may have used them near HOT cathode resistors...
...not sure though.

Cheers.

Si.

[Elvee]

Originally Posted by The Space Egg Corp

So...not sure there was any great 'audio advantage' in a Grundig TV set...
...I wonder why they used the EK's as opposed to regular 'metal cans' ?

I don't think they were used for any audio advantage, simply they were low esr, suitable for power operation at 15625Hz, and the fact their case is thermoset is probably an inheritance of manufacturing traditions.
The epoxy sealing is also more durable and gas-tight than rubber, particularly in the hot environment of a TV set

Had wondered if it was a 'can insulation' issue...
...but I've not seen an EK series cap that is over 40v rated.
Did they come in much higher voltage ratings ?
Anyone know ?

63V was the maximum

Here is a thread where they were discussed:
Help to id the capacitors in my preamp

I just measured the esr (@1KHz) of some used ones:

100µ/16V: 295mΩ
47µ/40V: 249mΩ
220µ/16V: 130mΩ

I have other samples in my stock, but I may need some time to locate them

[The Space Egg Corp]

Hi Elvee

Thanks VERY much for that.
I thought last night...Yep...not audio, in the TV set's...but high-frequency.
BINGO !

And yes...
...manufacturing techniques !
Roederstein produced superb plastic film/foil caps...I have used loads.
All end-potted in resin.
Never seen a Roederstein product in a 'tin can'.

Thanks for the ESR figures.
A quick 'vauge check' suggests that the ESR figures are AT LEAST as good as Panasonic FC's...
...and in one of your examples; actualy better.
Not exact uF-V comparison, as values differ...
...but def. in 'the ball-park'.

I believe ESR can go up a bit, particularly with high-voltage/ripple etc. & time...
...so I guess it's possible, the one's you tested ( depending on use ) could have had ever lower ESR, straight from the factory.

And yes...also...no vent...totaly-sealed...
...as per Roederstein's plastic-caps...
...no air out...
...= no air in, either...
...I wonder if that prevents any internal oxidising ?

Still...the intrigueing use of 'Bakelite'...
...well past the end of the 'Bakelite-age'.
The Russians having said that, seemed to be still making terminal-strips & group panels out of Bakelite, untill relatively recently.

Perhaps again, a Roederstein 'legacy production technique'...
...or is there some other reason for the Bakelite construction...
...Resonance ?

Mmmm...?

Cheers.

Si.

[Elvee]

I am no material expert, but I don't think they are actually Bakelite, even if the material bears some superficial resemblance. At the time they were designed, many high perf thermoset materials already existed.

Original Bakelite included porous load materials like saw-dust, making it very poor regarding water absorption, strong bases or acids resistance, permeability, etc.

The guys at Roe and Siemens were real experts, and knew perfectly well what to use to achieve durability. The resin was probably urea/methanal or phenolic, or some proprietary mix with suitable inert loads to achieve (very, very) long term stability.

I don't think oxidization is a problem: on the contrary, it is necessary to maintain the oxide layer.

But the important thing is to prevent the loss of contents. Maintaining the oxide layer requires a small amount of electrolysis, of which the resulting gases are normally recombined thanks to additives, but ordinary caps with a rubber seal always lose some of their hydrogen in the process, and in the end when the supply is exhausted (~water content), the capacitor dries up.

A completely tight seal prevents any loss, but also demands an extreme purity and stability of the materials inside, otherwise the pressure would build up and make the capacitor explode (I have seen such capacitors explode when subjected to reverse bias).
This demands very high standards of manufacturing, because you have no right to error.
This is typical of the german industry at the time, they were also the first to be able to produce plastic film caps of a consistently high quality, and this was no mean achievement (I have some Hunts samples of that time which by contrast were complete failures due to poor quality control at every stage)

[Preamp]

Originally Posted by The Space Egg Corp

Never seen a Roederstein product in a 'tin can'.

There you go.

[Elvee]

Originally Posted by Preamp

There you go.

Indeed, see pics. I also have earlier examples, contemporary of the EK, or even predating them (but here again, locating them might take some time).
But as far as I remember, the quality was.... let's say ordinary.

By contrast, the Siemens in Al case of that time were as outstanding as the GSF types

[The Space Egg Corp]

Thanks Preamp !

Now I have seen a Roederstein product in a 'tin can' !!!

Si.