200S multi cap can replacement

[Tbass]

I have a choice of multi cap cans to replace the original multi cap can in my 200S;  valued: 30/20/20/20 525v, but I dont know what the consequences of using a can with much higher mF values.  The replacement cans Ive found so far, both at dynakitparts.com, are valued: 30/20/20/20mf - 550/600v and 80/40/30 (@525v)/20 550/600v. I plan on retaining the GZ34 tube rectifier and buying a set of 4 tubes (tubesandmore.com) of 2 wing C 6550s, a JJTesla GZ34/5AR4, and a NOS 6AN8A.  Could anyone share some experience on higher mF multi cap cans and/or the tube brands and anything else pertinent with me? Thanks much.

[Greg_M]

Are you concerned about voltage or mfd ?
The first one you show (30/20/20/20mf - 550/600v) is a direct replacement, it just has higher voltage capabilities, which has no effect on sound.

I'd stay with the original specs whenever possible

[Soundmasterg]

Be advised that the 200S and most of the other large tube (KT88 or 6550) bass amps have internal voltages that are much higher than they were when the amp was new due to the higher wall voltages these days. These higher voltages are higher than those replacement can caps which lowers their life span and in some situations, could cause the caps to blow. Moreover, the suppliers of those can caps that are exact replacements these days are limited, so as a consequence, prices are higher. You can save money and get better performance by using smaller, discrete caps instead of the big can. You can hook the first two filter stages up in series, along with a resistor in parallel with each cap, and get a 600v or 700v rating, and still have close to or the same value as was stock in the amp. You can also choose to use higher value caps  which will give the amp less hum and a quicker response for the bass tones, which translates to a slightly tighter bass sound, which most bass players like a lot. The only caveat with using larger cap values (not voltage values but the mf/uf values) in the first stage is that anything past 60uf total and the GZ34 tube rectifier can not handle it and will blow. When you hook up caps in series, the uf rating is halved and the voltage rating is doubled, so for two 220uf 350v caps, you essentially have one 110uf 700v cap. This value would not get along with the tube GZ34, however you could use a solid state Weber Copper Cap which emulates the sag and voltage drop of the tube rectifier. The second stage could get two 100uf 350v caps in series for a 50uf 700v cap. I don't recommend changing the other filter caps to larger values because they are in the preamp, and because of how they are connected to the preamp, if you change the value of them, it will change the sound. Changing the first two cap values only changes the feel of the amp. As I said however, you can go with stock values of the caps too, but the higher voltage rating is a very good idea and I suggest it no matter what you do otherwise.

The tube choices you have picked are fine, though I prefer the JJ KT88 in my Sunn tube amps, but those Winged C are good tubes and work and sound fine. I have some in my Ampeg SVT and they have been perfect in that amp for years.

Greg

[Greg_M]

What higher voltages? Are you talking about at the wall?
I've heard several people mention "higher voltage" and I am curious as to what you/they mean

I've researched using separate caps instead of a can and sadly it's not cheaper. The 30mfd is doable but the 20s are about $11-12 each, so when you add it all up it's cheaper to get the can.

[biltmore]

If it's the can cap that I'm thinking of, I've had a couple of reputable techs tell me that it won't last that long. It's almost a temporary solution (6 months if I recall correctly).

[jaywalker]

As a general rule the capacitance value can vary +/- 20% without noticeable effect (other than the imrovement of having good caps) but the voltage rating should be equal to or higher than what you are replacing...higher voltage beyond a point is of no benefit. A lot of older cap values combinations seem to be scarce if not impossible to find so sometimes it is expedient to use separate caps mounted under the chassis.

Re: higher wall voltage. Easily overcome with a bucking transformer which can be homemade or store bought. Mine knocks down the wall voltage with a switch. either -6V or -12V, from 120V to 114V or 108V. Best I can figure is that wall voltages changed upward somewhere in the mid to late sixties/early seventies from 110 to 115/117 then later up to 120...actually higher in places and at different times of the day. So for amps from the fifties and early sixties I'd shoot for the 110 range...later amps up to 115 at least up to the eighties.

[EdBass]

Re: higher wall voltage. Easily overcome with a bucking transformer which can be homemade or store bought. Mine knocks down the wall voltage with a switch. either -6V or -12V, from 120V to 114V or 108V. Best I can figure is that wall voltages changed upward somewhere in the mid to late sixties/early seventies from 110 to 115/117 then later up to 120...actually higher in places and at different times of the day. So for amps from the fifties and early sixties I'd shoot for the 110 range...later amps up to 115 at least up to the eighties.

To my way of thinking, that’s a much less “user friendly” solution than fortifying the filter capacitors, but it would work; but I think I would suggest a variac rather than invest in a fixed transformer.
Far more useful for other applications, and adjustable to give your rig the exact voltage required, regardless of the specific wall voltage in any venue that might need “massaging”.

But the underlying issue goes beyond wall voltage IMO.
Obviously the increased average wall voltages from 1957 as compared to modern day are a contributing factor, but I think it’s more of a basic design flaw of the original Dynaco design. The OEM can caps in the power supply are just not rated at a high enough voltage for the OEM power transformer, and can cause the can cap’s first section to see higher than its rated voltage every time the amp is turned on. The OEM caps are rated for 525 volts, and the B+ can easily hit or exceed 585 volts during start up, largely because the rectifier heats up and begins conducting before the power tubes heat up and start drawing current. Even the beefier and costlier 550VDC can caps available now are being stressed beyond their ratings, albeit claiming a “peak” rating of 600VDC.
Plus, the inside of a gigging amp is a pretty hostile, high temperature and high vibration environment for any components, and IMO a rating higher than the anticipated voltage is preferable, at least for the first stage.

And… That’s if you decide to stay with a tube rectifier, which Sunn decided to eliminate (wisely IMO) in 1969-1970.
Even worse news; of course with a SS rectified there is zero lag for heating before conduction starts, and because of the more efficient operation of the SS diodes over a vacuum tube rectifier, the cap can be slammed with even higher voltages, without any "lag" for the power tubes to start conducting. 


However, that being said I have several old, regularly used Sunns that still sport their original can caps, and they test and sound fine, so what do I know? 

[arskas]

Hey thanks for this thread guys! It's great to read about this just now because I'm in the process of cloning a 200S amp. The multi cap can is available here in Finland but I think I'll have to use some series connected caps also.

[Greg_M]

I have a UPS on my computer and on the front of it is a digital display that shows line voltage.
I varies constantly from 110 to 125. As of this writing it is 122.4 as measured with my Fluke meter


My next project, which will run in parallel with building the 200S speaker enclosure, is building a 200S equivalent amp. (Basically a Dynaco Mk III with built in preamp) I plan to use the higher voltage 30/20/20/20 (550-600) and call it good.

However, for the experimenter, you can set up your own capacitor system with some calculations on these two pages.....
http://www.tpub.com/neets/book2/3e.htm
http://en.wikipedia.org/wiki/Capacitor

However it might be wiser, economically speaking, to just buy two higher voltage can caps now.

[CLD]

I've measured my outlet voltage as high as 137, and usually it's between 125 and 135, so I use a big Variac to throttle it back to 115 or so. Keeps the old tube amps happy ...

[Greg_M]

I think I would have a conversation with the power company if it's that high. If you have underground power, there are some taps on the transformer that feeds your house that can be changed. 137 is crazy high.

[EdBass]

My next project, which will run in parallel with building the 200S speaker enclosure, is building a 200S equivalent amp.

Speaking of which; do you still need the measurement "F" on your diagram?

I plan to use the higher voltage 30/20/20/20 (550-600) and call it good. However it might be wiser, economically speaking, to just buy two higher voltage can caps now.

I've used them, they work fine. But so do the 40 year old 525VDC OEM caps in several of my old amps, as I mentioned in my previous post. I also have an cap board from Triode in a SS rectified 2000S, and that amp flat kicks *ss.



I think that particularly if you use a tube rectifier, and specifically if you are building an amp for personal use and can work on it yourself I agree it's by far the easiest route to go.
Plus, it saves a whole bunch of real estate in the chassis, and it’s light; only 68.4 grams as compared the 48.4 grams for a single Sprague Atom 20uF electrolytic. The cap board was easy in the 2000S because there is a ton of room, it would be a lot tighter in a 200S sized chassis.
A 60 watt all tube amp is never going to be light or ultra portable of course, but every little bit helps!

While I admit it’s certainly close enough to probably not lose sleep over, the whole “over voltage” thing kind of bothers me though, and also I’m a big fan of SS rectifiers, particularly in a bass amp design.
In the past few months I’ve tested SS and tube rectified 200Ss side by side, in my shop and in live gig situations, and not surprisingly there is a fairly noticeable difference, the SS rectified amps just sound bigger, cleaner and deeper; same tonal nuances and character, just like the “on steroids” version.


Someone should commission a 30/20/20/20 600VDC can…

[Greg_M]

I've got the thing CADed out and by putting together all the different dimensions everyone gave (including "Conrad's Dream" article) I was able to figure it all out (I think).

I cut the horn groves and did the rabbets yesterday on the CNC mill. It only turns 6000 rpm so I was a little concerned, but it worked like a charm. I glued the top (or bottom) to one of the sides today.

I haven't contributed anything lately, (picture/drawing wise) because I am still fighting with the virus on my windoz computer and I am on a Linux computer now which does not have the CAD program and upload program. I don't want to risk infecting anyone so I won't hook that computer up to the internet until I am sure it's clean.

I would like to see some close up pics of the wiring of a 200S chassis though, if anyone has any. The biggest chassis I can find is 17" by 10" so mine will be a little smaller than stock.


Sorry for wandering off topic

[Soundmasterg]

What higher voltages? Are you talking about at the wall?
I've heard several people mention "higher voltage" and I am curious as to what you/they mean

I've researched using separate caps instead of a can and sadly it's not cheaper. The 30mfd is doable but the 20s are about $11-12 each, so when you add it all up it's cheaper to get the can.

The wall voltages are what I was talking about, and of course having a higher wall voltage means higher voltages inside your amp too....and it is not a linear relationship. Going up 15 volts in the AC supply voltage could mean your amp goes up 50v or more with it's internal DC voltages. My 1970 200S with the Schumacher transformers has about 560v on the plates of the tubes with a 125v AC source voltage and a Weber Copper Cap rectifier that emulates the voltage drop and sag of a tube rectifier. The vintage cans lasted a long time because they were well made back in the day since they were used in just about everything consumer related. The modern cans are not as well made and many techs have had trouble with reliability with the ones that CE Distribution/Antique Electronics makes and sells among others....enough so that they will not use them in repairs as a result. Can caps were used originally as a money saving measure because having one part that is put into a spot on the chassis and 4 wires are hooked up to is cheaper to produce than having many caps having to put into their proper spots and hooking wires to. Also, back in the day, because so many can caps were used for tube TV's and other consumer gear, they were cheaper in many cases than discrete caps. Since you are planning to build an amp from scratch, you can go for the best for performance reasons if you want to. Can caps are definitly NOT the best solution these days for the reliability factors if nothing else. In addition to what I mentioned, the only reason the can caps are made in multi values like what was used in the Sunn is because they were used in some amps like Sunns that were based on consumer equpiment (Dynaco hi-fi amps in the case of Sunn).

The other point is that discrete caps are indeed cheaper than using a can. I am guessing you looking into using Sprague Atom caps for your build? These are overpriced and much larger than they need to be with today's improvements in capacitor design, AND the manufacturer of the Sprague Atom caps even suggests that they do not get used for new designs. They are only made to fit into older designs that used them originally. If those are the ones you may have been investigating, then you may have been buying into the hogwash that people like Gerald Weber put out there about only buying US caps like the Atoms, etc. There are many good discrete caps that you can purchase these days that are cheaper than what you mentioned. The 20uf 450v ones that Ted Weber sells are very small and work great and are quite cheap. At last check they are $1.25 each. Mouser and Antique Electronics also sell some great quality caps like the F & T's or Xicons. I would personally stay away from illinois caps which I have had failure troubles with in the past, but pretty much Nichicon, Rubycon, Xicon, etc., that Mouser sell are just fine, and are all cheaper than the $11-$12 each that you mention. The F & T 22uf 500v cap is about $5 each from Antique Electronics and is made in Germany and is great quality.

For bass amps, solid state rectifiers and larger filtering makes a huge difference, speeding up the amp and making the bass tighter and quicker, yet the amp still has that tube warmth. Moreoever, the reliability of the tube GZ34's being made today is not very good. If you played an amp with either design, I would guess you would go for the solid state rectified one every time if you intend to use the amp for bass. There were several design issues with vintage Sunns that could be improved on these days. For instance, good layout specifies that you keep your sensitive grid wires away from noisy things like plate and heater wires, and if you have to have them near to each other, that you should have them cross at right angles to each other, yet in the vintage Sunns, they ran all of them in parallel in the wire loom. They get away with it in most cases because the amps don't have very high gain, but the amps hum more than they should as a result. Ask Conrad if he had to redo those amps today if he would make changes or not and see what he says. I would bet that he would agree with me on most counts.

Making your own amp is admirable, though it will be more expensive than purchasing one used. If you've never made an amp before, then you could run into troubleshooing issues once it is built to eliminate hum, oscillations, etc. That said, it is a fun hobby and can be very rewarding. Good luck on whatever you decide to do with it.

Greg