47k/.05uF Rk/Ck?

[Don Moose]

Hi - working on a 60's vintage HiFi that's sounding 'thin'
It's not the speakers as another set sounds the same.

Looking for where to start - most of the Ck parts are ceramic disks. The one's that aren't are the last stage before going off to the PIs and they're Aerovox .05mF white paper tubes in parallel with 47k resistors.

Does that sound reasonable in a HiFi?

[guitician]

That should start to rolloff around 65hz, which should be OK for a bookshelf speaker. Are the ceramics .05 too? What type of output power?

[Don Moose]

This is the unit. A pair of 6V6s per channel. I haven't dug in too deep, but I think it's cathode-biased, so I'm thinking we're under 10W per channel - definitely under 20. The speakers are Jensen 3-way sets with 12" woofs.

The ceramic values I see range into the .001 area, with some lower values in non Ck roles.

Does the Rp value play into the rolloff calculation? I haven't looked at those.

[guitician]

Ok, nice. You may want to parallel that 150/50 section, which I'm guessing is the bypass for the cathode resistor common to all four tubes, with a known good cap of similar capacitance, to see if you get any more bass. Have you tested the 6v6's?

[Enzo]

I'd be changing the paper caps.

Looks like I never got on that thread, so i didn;t see your question about a stylus.

Parts Express has a stylus page. If this is the old flip stylus for 33/45 or 78, and thus likely a ceramic cartridge, then I may have something here in the warehouse. But as with so many things, enter phono stylus into google, and stand back.

[Don Moose]

Thanks guys - in part I'm asking about the value on these Aerovoxen because the whole MF/mF/mmF/uF thing has me puzzled about order of magnitude.

Still, if 0.05uF||47k knees at 65Hz, then 0.05mF (50uF) would be 0.065Hz so I'm more comfortable.

Do I look for paper to replace, or go with some modren poly/film type?

Haven't tested any tubes - may swap them around a bit to see if problem follows any one in particular.

Not worried about the stylus yet, haven't gotten around to getting the platter to spin.

Thanks again!

[Enzo]

AH.

When we write uf for microfarad, that isn;t a "u." It is the lower case Greek "mu." But the thing looks a lot like a script u in English, plus it is the closest we can come on a conventional font. But the mu really stands for the first letter of micro, which is m. It stands for 1/1,000,000th of a farad.

In days gone bay, like when tubes were all ther was, the time of your amplifier, they often used "m" instead or "u." So uf and mf were the same thing. In those days a 1000uf cap was huge. And that was a 1millifarad cap, which would be the only time we might use millifarads.

"f" of course stood for farad. And a 1 farad cap - 1f - was somthing one could talk about as an abstract for some discussion, but no one would have made one, let alone put them on the market. Nowdays guys put multifarad caps in car stereos.

"m" nowdays means mostly "milli." As in 1/1000 of something. We could talk of millifarads. A 1000uf is 1mf, after all. I don;t see it used, but it may drift into use. SO it is possible to confuse mf for millifarads, but the context should eliminate that possibility. .05millifarad would be 50microfarads. And it is unlikey you would find 50uf coupling caps.

Today we call 1/1000000 of a microfard the picofarad. 1000000pf is 1uf. So .000001uf is 1pf. A millionth of a millionth. We didn;t used to use "pico". We used micro-micro. In some sorta old drawings you might see "uuf" meaning micro-microfarad. uuf and pf mean the same thing. For the same reasons as discussed above, in even older drawings you might find "mmf" instead of "uuf." mmf and uuf mean the same thing.

Because of that mm in the mmf, at some point electrinc techs, and maybe mostly ham radio operators, took to calling that "mickey mouse." SO someone would talk about a "27 mickey mouse cap." It was funny once or twice, then it sounded stupid...even then.

Then there is nano. That is the 1000 step between micro and pico. 1000pf is 1nf - 1 nanofarad. That is more and more used these days. I won;t ever say it unless consciouosly trying to, but younger folks may find it natural to use. Seems to me it is more prevalent in Europe, but I could be wrong. But as 1nf replaces .001uf, I suppose it is possible 1mf will replace 1000uf in our daily speech.


SO to make a long story short... .05uf and .05mf are the same thing.

[Steve Conner]

Yay, capacitor trivia. Here's some more:

Some European keyboards can produce the mu symbol. In this day and age of Unicode, it actually works in forum posts, and Germans love to use it: 220μF. (I had to look it up in Character Map, though.)

Supercapacitors are now available in kilofarads: I heard talk of a 3.5kF one.

We use nanofarads in Europe, but not millifarads for 1000μF (there we go again ) Millifarads probably aren't used because of the risk of confusion with those old American schematics that used "m" to mean micro.

A common style when writing schematics is to replace the decimal point with the letter. 2.2 ohms becomes 2R2, 4.7k ohms is 4k7, 3900pF becomes 3n9, but for some reason 1000μF is still 1000u.

"Nano" comes from the Greek word for dwarf, ultimately the same root as "gnome". I wonder if gnomofarads will catch on.

http://members.optus.net/alexey/prefSI.xhtml

[martin manning]

I kind of like nanofarads... you only have to move the decimal three places one way or the other to get to pico or micro. A happy medium, maybe. The markings on small caps are mostly in picofarads (104 = 100,000 pf), which can get unwieldy, but with a system like that I guess one has to use the smallest unit, and it's easy enough to subtract 3 or 6 from the last digit.

MPM

[Don Moose]

A common style when writing schematics is to replace the decimal point with the letter. 2.2 ohms becomes 2R2, 4.7k ohms is 4k7, 3900pF becomes 3n9, but for some reason 1000μF is still 1000u.

"Nano" comes from the Greek word for dwarf, ultimately the same root as "gnome". I wonder if gnomofarads will catch on.

I'm using this style here becaues I tend to print B-size schematics (11x17") on A-size (8.5x11") and don't want to lose the decimal.

... gnomofarads I think gnomohenries might catch on.

[Jag]

Sometimes you scare me Steve!

[Enzo]

gnomofarad caps are only used as lawn ornaments though.

SOmetimes they install them under a bridge, but they they are called trollofarad caps.

Yeah, we can look up the code for mu to make it show up on the screen here, but seems like too much work to open up the character table - I have no idea where it is anyway - then type in a character string just so one letter shows up.

[Don Moose]

Ok, nice. You may want to parallel that 150/50 section, which I'm guessing is the bypass for the cathode resistor common to all four tubes, with a known good cap of similar capacitance, to see if you get any more bass.

So I poked around a bit with my DVM - there doesn't appear to BE an Rk for the 6V6s. The common Ck (which in itself seems odd to me) is that 150u Astron, which measures in the n'hood of 26 ohms.

The PI coupling caps hit the grids, and then a Yel-Vio-Yel (470k) resistor connected to GND via a tie point on an NC pin on the 6V6.

The K pins are common and hit that 150uF Ck, but no runs to an Rk that I can see anywhere - odd. It does run over to pin 5 of the 12AX7 that is the phono preamp which is NOT connected to pin 4 - _very_ odd.

[Don Moose]

After a little more thinking, this heater-as-bias-resistor sort of makes sense.

It wants to set Vk at 6.3V and have the sum of the Iks be 150mA (half the heater - pin5 to pin 9), so that's about 37.5mA each. A neat hack if it acts as kind of a regulator. Still, the heater for the phono stage seems a rsky place to go.

Seems to require a pretty fair match in the 6V6s, too.

[Don Moose]

I found 4 of the needed 8 .05 value in 630V mylar. Put those between the PIs and outputs. Will be going back for more soonish. Found some 0.1u in 230V mylar for the black tubes. Also paralleled a 100u and 47u 'lytic to sub in for the 150u Ck.

MUCH better. I still have the left-right imbalance, but only on the aux input - radio's fine.
May play with the components between the jacks and the selector switch.

Thanks again, guys!