Film Caps for Tube Amp Power Supplies

[R.G.]

BG Micro has 20uF 700Vdc caps, PCB mount, appx 1.65x1.54x1 inch, for $2.69 each.

[Leo_Gnardo]

Heck of a deal, thanks for posting it!

[SoulFetish]

BG Micro has 20uF 700Vdc caps, PCB mount, appx 1.65x1.54x1 inch, for $2.69 each.

My Man! Now you're talkin' I've been singing this tune for a couple of years now. The prices of power film caps (or "DC link" caps) have definitely become competitive with electrolytics, and the sizes have become more and more compact over the past few years.
I've used Vishay series MKP1848* with great success, and have found great prices on caps up to 100µF/500-700V when comparing prices on octopart.com. But Kemet, Panasonic, CDE, and others also have great offerings.

[Justin Thomas]

I'm trying to broaden my knowledge, to use parts that may be "unconventional." So, first, would these be usable in tube amp power supplies? I'm guessing the composition isn't what matters there - we used electrolytic because they fit thebill with high capacitance/high voltage?
Also, what do the terminals on these look like? I've had some luck mounting PC-mount components into properly laid turrets; could the same be done with these?

(I took a PCB-mount 12-position rotary switch, tgen mounted it on a tiny 1"x1" turret board, and used wire to duplicate the PCB traces that had been damaged. I put the switch terminals into what would be the bottom side of the turret normally)

Justin

[Leo_Gnardo]

I'm trying to broaden my knowledge, to use parts that may be "unconventional." So, first, would these be usable in tube amp power supplies? I'm guessing the composition isn't what matters there - we used electrolytic because they fit thebill with high capacitance/high voltage?
Also, what do the terminals on these look like? I've had some luck mounting PC-mount components into properly laid turrets; could the same be done with these?

(I took a PCB-mount 12-position rotary switch, tgen mounted it on a tiny 1"x1" turret board, and used wire to duplicate the PCB traces that had been damaged. I put the switch terminals into what would be the bottom side of the turret normally)

Justin

Film power supply caps work well with tube amps. I've stocked some for a couple years now, handy for old Ampegs with very high power supply voltages. But they are a bit cumbersome to mount, as they're rectangular. So far I epoxy them in far corners of the chassis, & wedge them into place using styro blocks cut from home sheet insulation scraps. Gotta run wires to them, as their leads are stubby, meant to poke thru printed circus boards. And you gotta be careful, they don't slowly lose voltage over time like electrolytics. Left charged, one can sting you months later. Ask me how I know! One thing's nice, you never have to worry that they'll go bad in a couple decades. Carr has been building their amps with Solen film filters for what, about 20 or so years now. tubesandmore / Antique has had 'em for a long time. Solens are cylindrical, a good bit larger and heavier than electrolytics, and have reasonably long leads like el's. But no knock down bargain prices on 'em.

[Justin Thomas]

Thanks Leo! I would ask if anybody has a picture?
My idea is basically that the turrets serve as the PCB holes, and I wire to the turrets. As power supplies are fairly simple, it's not so bad... So even stubby leads may not be an issue...

Justin

[SoulFetish]

Thanks Leo! I would ask if anybody has a picture?
My idea is basically that the turrets serve as the PCB holes, and I wire to the turrets. As power supplies are fairly simple, it's not so bad... So even stubby leads may not be an issue...

Justin

the leads aren't long enough( in most cases ) to use with turrets, so I use eyelets to mount them, and use turrets for all other components.



I'll try and grab a pic of an unmounted component, but the leads are maybe around 8-10mm... Actually, I found some datasheets I compiled. I've attached them as a single PDF below, as well as an article on film caps by Vishay
MKP1848_type_datasheets.pdf
Vishay General Film Cap Info.pdf

[R.G.]

I'm trying to broaden my knowledge, to use parts that may be "unconventional." So, first, would these be usable in tube amp power supplies? I'm guessing the composition isn't what matters there - we used electrolytic because they fit the bill with high capacitance/high voltage?

Yep, the idea is that you'd replace the high voltage electros with high voltage films. It used to be (1940s and 1950s) that oil-filled film/paper caps were the normal thing in tube equipment. Then electros with enough voltage and ripple current ability took that job away from them. The down side of electros is the fact that they will wear out sooner or later.

I concocted this idea in my head of an "Immortal Amplifier" where I'd replaced everything that has a normal wear-out, excepting tubes, with things that aren't expected to give up the ghost in a few decades. The film caps fit the idea for power filters.

[Justin Thomas]

Thanks R.G.! I always thought it was something special about the way lytics worked that made them popular for power supplies; turns out it's not the case.

Justin

[mikepukmel]

Way cool, RG. (my spidey senses are anticipating an "out of stock, expect more soon" message on their site!!!!)

[R.G.]

I always thought it was something special about the way lytics worked that made them popular for power supplies; turns out it's not the case.

Well, maybe. Electrolytics are not pure capacitances. In addition to the raw capacitance, they have internal inductances and resistance (ESL and ESR) and leakage resistances. These 'impurities' are present to varying degrees in all capacitors, and there are others as well. Given the common human failing to see patterns in anything ( even if they are there ) and the tendency for guitarists to think that the perfect amp/guitar/effect/whatever was made some time long ago and "the don't make 'em like that any more", I think it's very likely that there will be some amp and guitar enthusiasts that will swear that there is a "sound of power filter caps" that only electrolytics can give. It would be interesting to measure some reputedly Belchfire Megablaster vintage caps to find their particular mix of leakage, ESR, and ESL, then dirty up a theoretically more perfect film cap to match, then see if an electrolytics-purist can tell the difference.

[Mike Sulzer]

Well, maybe. Electrolytics are not pure capacitances. In addition to the raw capacitance, they have internal inductances and resistance (ESL and ESR) and leakage resistances. These 'impurities' are present to varying degrees in all capacitors, and there are others as well. Given the common human failing to see patterns in anything ( even if they are there ) and the tendency for guitarists to think that the perfect amp/guitar/effect/whatever was made some time long ago and "the don't make 'em like that any more", I think it's very likely that there will be some amp and guitar enthusiasts that will swear that there is a "sound of power filter caps" that only electrolytics can give. It would be interesting to measure some reputedly Belchfire Megablaster vintage caps to find their particular mix of leakage, ESR, and ESL, then dirty up a theoretically more perfect film cap to match, then see if an electrolytics-purist can tell the difference.

And why not? Pentodes (or beam power tetrodes) in a double ended transformer circuit have some power supply rejection through balance in the "A" part of the "AB" operation, and also because they are sort of current sources controlled by the grid cathode voltage. The second is lost when the output stage operates in the non-linear range. The ripple voltage modulates the signal, and its details are a function of both capacitors and rectifiers. If this matters, then 50/60 Hz probably does, too.

[SoulFetish]

I’m sorry, I call bullshit that anyone can hear the difference between film and electrolic caps in the power supply, or any significant difference between 100/120Hz ripple modulation either. I’m not saying the difference isn’t there, but until I see some convincing data, from double blind testing, i will remain highly skeptical that either contribute anything significant to the overal sound

[Chuck H]

I’m sorry, I call bullshit that anyone can hear the difference between film and electrolic caps in the power supply, or any significant difference between 100/120Hz ripple modulation either. I’m not saying the difference isn’t there, but until I see some convincing data, from double blind testing, i will remain highly skeptical that either contribute anything significant to the overal sound

That's where the trouble is. Most designers know that an amp has a job to do and don't fret about those small differences. A good amp is a great amp in the right hands. And I think that most often it's the hands that make a real difference. But indeed some players may be able to hear/feel a difference. Intermodulations, feedback and phase errors occurring due to even small differences in power supply impedance are real. I know you've acknowledged that. I think it's most significant in overdriven amps. And I do think some players notice. But to back your play I would absolutely agree that in a full live band, mixed venues sort of environment that even those players would be hard pressed to notice a difference. Not just listening, but playing through an amp. And I think most builders and designers would agree with that and I think THAT's why there not much data, but instead just spotty reporting on the matter. All I'm saying is that it's real and audible. A lack of documentation for the phenomenon in an arcane field like "overdriven guitar amps" hardly seems like proof of absence for the affect.

[Enzo]

Keep in mind too that parts are not generic monolithic things. Meaning all 40uf 500v electrolytics are not the same. And all film caps are not the same. You might find just as much difference between two e-caps as you do between an e-cap and a film.