S5 Amplifier Kits

[DuncanM]

Greetings,

Has anyone had any experience with the new S5 electronics "L series" amplifiers. These all use 5670 triodes driving PP pairs or PPP quads of 6005 pentodes.

http://s5electronics.com/ltube.html

Thanks,

Duncan

[EWBrown]

Interesting, a definite step-up from the earlier 11BM8s and 11MS8s versions. Trying to match up pairs of the triode/pentode combos can be rather challenging, these new tube choices make that a lot easier Yellow_Light_Colorz_PDT_03

5670s can be directly replaced with 2C51s and WE396As, and 6005s are directly interchangeable with 6AQ5s. Of course,the first thing to do is not use those cheap little brown 0.22uF mylar coupling caps, use some WIMA box caps, IIRC, the 0.15 uF/400V red "box" caps will fit perfectly, at least they did on the K-502 and K-12s. Forgo the wooden base and use a real chassis, and better RCA inputs, and volume pot, and speaker binding posts. They really "cheap out "on those, but then it keeps the base costs down .

IIRC, Bendix Red Bank had some guided-missile, indestructable, super-mil-grade-overbuilt version of both the 6005 and 5670. Yellow_Light_Colorz_PDT_11

(Oh, man I'm getting goose-bumps just thinking about it) :o Yellow_Light_Colorz_PDT_01 Yellow_Light_Colorz_PDT_02 Yellow_Light_Colorz_PDT_06

Either way, I'd still ditch the original OPTs and go with UL on them, 8 to 10K P-P for the 8 watt version, 5K P-P for the 16 wat PPP version.

Never being one to not put my money where my mouth is, I just ordered one of the 16WPC stereo kits :o




Nice big photo, viewed this way... I see they use GE JAN tubes, too! :o

OK, here it is (drum roll please). They made that almost too easy Yellow_Light_Colorz_PDT_02

Basic K-12M schematic, but change the VA plate resistor to 220K, 1/2W; change the PI plate and cathode resistors to 68K, 1/2W; insert a 200 ohm, 1/2W resistor in series with each screen grid.
Increase the B+ slightly (from 200VDC to around 225VDC, with at least 200 mA current capability). Filament winding for the 16WPC version 6.3V, @ 4.3A minimum. For each quad of 6005s, the shared cathode resistor is 150 ohms, 3W. For the 8WPC version, the RK will be 300 ohms (as in the original K12M).

The supplied electrolytics are 220 uF, 100 uF and 22 uF, all at 250WVDC rating. THis is pushing it real close to the edge of the safety envelope, as the B+ can creep up to 232VDC during normal operation, and shoot up to over 260VDC if the tubes are not installed. I'd go with 350VDC, and even 450VDC wouldn't be extreme...

Now, that is one cost-cutting approach I'm not too excited about, go with 600 ohms for each cathode, and bypass each one with 100-220 uF / 25-35VDC. Unless you have nicely matched quads, there is going to be some major imbalance with a single 150 ohm Rk.

Besides, a 3W 150 ohms resistor is gonna run kinda hot...
Yellow_Light_Colorz_PDT_09 Yellow_Light_Colorz_PDT_13

These appear to use the same "UTK" OPTs as used in the K-12M, (9600 ohms:8 ohms) and a much beefier power trannie, for either version (I'd use Hammond 1609 for 8WPC, and 1620 for 16WPC). Convert to UL, the individual 200 ohm SG resistors make this really easy...
NFB resistor is 68K bypassed with 33pF as used in the K-12 , YMMV, the actual resistance value may need some future tweeking.

(Update: The supplied OPTs are about the same size as the old UTKs, but have a different part number and the cores are oriented vertically, as is the power trannie)

/ed B in NH

[TerrySmith]

I too may order one of these, the more the tube count the better! Yellow_Light_Colorz_PDT_07 Might even spring for the preamp too.

[Ty_Bower]

Ignoring the obvious pinout differences, is the 5670 like something halfway between a 12AT7 and a 12AU7?

Why use a quad of 6AQ5 equivalents, when a pair of 6BQ5 will put out the same power? Unless of course you just gotta have a big pile of shiny hot glass. :)

I wonder if the printed circuit board would have any use as a starting point for a quad of 6BQ5, assuming you can figure out where to fit the necessary power supply upgrades...

[EWBrown]

I think their tube choices are driven by economics, thes 5670 and 6005s are fairly cheap (I ended up with lots of both types for free at an NNETG meet about three years ago).

The 5670 / 2C51 / 396A has a gain of around 35, a 12AU7 is around 17 and a 12AT7 around 60-something, a little less than a 6SL7 or 5751.

Between using tube-cad and the "old school" method, I've already re-designed this into a 5670 / 6005 (or WE396A / 6AQ5) VA / LTP circuit, something between Poseidonand Roy Mottram's VTA-70. If I use an LM334, then it's more Poseidon'like. If not, then I use a -34VDC rail and ithen ts closer to the VTA-70.

By changing (adding) a couple resistors I can be almost identical to the VTA-70 which requires no negative voltage for the LTP "tail".

I run this VA stage at 210VDC @ 1.05 mA, and the PI at 220VDC @ 3.2 mA (per channel). This allows for 250VDC B+ for the 6AQ5 / 6005s, and some CRC isolation between the driver, PI and PA stages. If I go that direction, then it's going to be 10WPC, with fixed bias, or 20 WPC, PPP, fixed bias. At this stage, it's still just a paperwork exercise...



(from using Tube Cad I calculated that the S5-L16 runs around 0.8 mA for the VA and 0.7 mA for the splitter, for each channel. Tube CAD screams out "insufficient plate current, plate voltage, lions, tigers and bears, oh my!"
Yellow_Light_Colorz_PDT_03 Yellow_Light_Colorz_PDT_01 :o

A quick "old school" SWAG indicates the 6005s should run around 24-25 mA each, presuming 220VDC B+ and the shared 150 ohm cathode resistor for each quad of tubes. Should be fairly easy duty on these tubes, and they shouldlast a LONG time Yellow_Light_Colorz_PDT_03

FWIW, they "cheat" a little with the OPTs, as the 16WPC amp is spec'ed as having 4 ohms output impedance, this would "reflect" back to the OPT's primary as being 4800 ohms P-P (OK, 5K to keep it simple).


/ed B in NH

[DuncanM]

A couple of questions and a couple of ideas:

Two problems with the K-12s were the PCB ruggedness and the location of the filament traces on the boards. If anyone has seem a board, are either or both of these improved?

If you mounted the electrolytic caps and fuse holder on the bottom of the board, it looks like you could mount the whole thing on the underside of a top panel a la the DIY35.

Speaking of the electrolytic caps, there is an awful lot of space around them--any problem with increasing the values?

Duncan

[EWBrown]

I've built the older K502s, so that they would fit under a metal chassis. The smaller components can mount either on top or bottom of the board (I put Resistors on top, along with ceramic tube sockets). The taller parts like caps, can go on the bottom. The supplied pot shouldn't be bottom mounted, as its connections will then be reversed, and then CCW is "full blast"... :o Yellow_Light_Colorz_PDT_21 Yellow_Light_Colorz_PDT_07

The boards are nowhere nearly as rugged and solidly made as the DIYtube35 boards are, so some additional care and planning will be necessary...

I've used additional electrolytic caps, the best approach for this would be to use a four-diode brige mounted on a terminal strip, and one or two 470 uF / 350V or (greater) caps mounted under the chassis, the existing electrolytics can be botton mounted, or in the case of the 220 and 100 uF caps, the leads are long enough that they can be laid over "sideways" then mounted.

I'd ditch the supplied volume pot and replace it with the 100K stereo pot from Radio Shack, and use chassis-mounted RCA inut jacks and standard "5-way" binding posts fo the speaker outputs.

I am not sure how the filament traces are laid out on this board. My kit should be arriving later this week, so I'll figure it all out. as I proceed..

BTW, Kathy at S-5 Electronics tells me that I'm the first customer for this kit, so it will be a learning experience for them as well as for myself ... Yellow_Light_Colorz_PDT_02 Yellow_Light_Colorz_PDT_11

The ultimate "fix" for any filament voltage induced hum, is to rectify and filter it into 6.3VDC. 8 6005s and 2 5670s require 4.3 amps total current.

[jduffy]

BTW, Kathy at S-5 Electronics tells me that I'm the first customer for this kit, so it will be a learning experience for them as well as for myself ...

Right on! Look forward to watching you build and tweak this.

A bit like landing on the moon for the first time!

[EWBrown]

Well, they earn one big "zinger", they forgot to put in the 68K resistors in my kit Yellow_Light_Colorz_PDT_21 :o Yellow_Light_Colorz_PDT_17
Fortunately I had some on hand (68K, 1% from Mouser).

The board seems to be of a better quality and layout than the old K502 /K12M series of PCBs. Board sIze is approximately 6 3/8 X 9 1/2 inches.


I assembled the PCB, subbing some WIMA 0.15 uF "red box" caps in place of the brown mylars, and 33 pF silver mica in place of the disc ceramic in the NFB loop.

I'll use some beefier OPTs, the little UTKs will work, but they'll be sweating hard... :o I've decided to go with Hammond 1615s.
They are 5K P-P, 15 watts, 100 mA, have UL taps and are about $42 each from AES.

Otherwise it'll be more or less "stock"at first, any UL mods, etc, can come later on, once I evaluate how it performs.

/ed B in NH

[EWBrown]

Well, I finally got this amp running this weekend, and it sounds pretty darn good! Other than some missing 68K resistors and a couple wood screws (I had plenty of both items already on hand), everything went smoothly and flawlessly.

I built it 99% "stock" for now, except for the six coupling caps, for which I used WIMA 0.15 uF / 400V, and replaced the ceramic 33pF disc caps with 33 pF silver mica (in the NFB loop).

For now, I'm using the original OPTs (they look similar to the old style UTKs shown in the large format photo, but have a different part number, and the cores are oriented vertically, unlike the UTKs).

Later on I'll try some Hammond 1620s, (I Had considered 1615s, but then I already have some 1620s on hand) and see if they sound better (they should).

For now, the whole "mess" is mounted on the supplied wooden board.

(Update: I just "scored" an oddball 18 X 7X 1.5 inch chassis box out of the "scrap" pile, this may work out well for this board, with power trannie on the left hand end, and the OPTs on the right hand end., and the PC board oriented between the two sets of iron. A bit of rework (or build a new one) and the board can fit inside the chassis, rather than sitting on top).

It definitely sounds a lot better than I expected, virtually no hum (I had to stick my ear right in front of the speaker, and could barely hear anything - this is much quieter than the older K12s and K502s). There is very little noise, just a barely discernable "hiss" with my ear right in front of the tweeters. I'd SWAG that the small amount of hum is AC-coupled via magnetic field, as all the iron has the cores oriented in the same vertical plane.

An ST35 still beats it hands-down for overall sound quality, but then it costs about 3X more to complete! I'd say that the claimed 16WPC is a bit optimistic, my SWAG is closer to 12WPC, before the distortion starts to creep in. That will be addressed in future mods (see below).

Some stats: The B+ at the OPT CTs is 230 VDC, the screens run around 225VDC, and the VA / PI runs around 215VDC.

The power trannie HV secondary, under load is approx 186VAC (it varies between 185 and 188 VAC, as the line voltage also varies). Current has to be at least 200 mA after rectification. The filament winding was 6.39 VAC with 4.3 A current loading. The power trannie was warm, but not burger-sizzling hot after a couple hours operating laser-guided IR thermometer. Yellow_Light_Colorz_PDT_11

The voltage across the 150 ohm "shared" cathode resistor is around 14.4VDC (I had 14.2 on one channel , and 14.6 on the other). That equates to around 96 mA per quad, or 24 mA per tube, assuming that they are reasonably closely matched. That is running the tubes very "easy" as they are rated at 35 mA PP and up to 45 mA in SE usage, at 250VDC. Take 'em up to 250VDC and 35 mA per tube (will require a beefier PT) and then they could kick out closer to 20 watts per channel.

The only follow-up mod I did was to bypass the 150 ohm resistors with 47 0 uF / 35V caps. This seems to improve the bass response a little.

I also temporarily replaced the supplied 5670s with some vintage WE 396As, and noticed a slight improvement, though I would have to make actual measurements in order to eliminate any suspected "placebo" effect... Yellow_Light_Colorz_PDT_06

For $200, it's a great deal!

I may get a second kit, in order to give it the "frankenamp" mods and upgrades treatment...

Update 22-Jan-2008: I guess the first one was sold to me at a "bargain" price, the price has now gone up to $225 from 200. :o Still, not too shabby...

I haven't yet done any further upgrades or mods, and it is still on the original supplied wooned board "chassis".

/ed B in NH

[jduffy]

Thanks EW for being the first to try this new kit.

I think this might be my Xmas gift to myself this year. It should be fun to build and tweak during the winter.

Please post whatever changes you do to this amp as I'm sure I'll want to try them myself.

[EWBrown]

I'm already thinking "version II" of this amp... Maybe get the monoblock boards (or hack a stereo 16WPC, in order to electrically isolate the two channels) and use one of the AN-TEK 230 & 230VAC toroids to supply a higher B+ and current for the 6005s. With the two separate 230V secondaries, I could go true "dual-mono" amd kick it up to 20 WPC, and use Hammond 1620s for the OPTs.

I look at these S5 kits like one would look at a Harley, no-one ever leaves it "stock" for very long...

I already have the OPTs and the AN-TEK toriod (originally bought for a 6V6 / 7EW6 project that hasn't yet materialized beyond the "paper" stage of development.

The Toroid would be SERIOUS overkill, it could power several of the 16WPC channels, and have lots of B+ power to spare... Onewould need additional 6.3V filament power, however...

OTOH, the lightly loaded original power trannies will have lots of reserve current and somewhat higher B+ available, which means NO 250VDC electrolytic caps in the PSU, TYVM Yellow_Light_Colorz_PDT_02 as they are already pushed right to the edge of their safety envelope, in the stereo version.

/ed B in NH

[RuralUrban]

My first hifi tube amp was a pair of the K-501 mono units. I used a Hammond chassis to put them in and I upgraded the OPT's to 1609's - and added many of the popular other mods. I went back thru my receipts and added them up and got to just over 300 dollars. ($180 for two mono kits, $60 for hammond steel chassis w/bottom and cage, and $70 for the pair of 1609's)..
In checking out the prices for the new S-5 kits, the next logical step for me would be a pair of the PPP mono kits, which are $163 each.....they would fit in the same hammond chassis, and I would also need a pair of 1620 OPT's which go for about $85 a pair at AES...This pushes the budget out to about $475, assuming I have nothing on hand (which I dont right now).....
This would create a true dual mono amp that is about the same power as an ST-35, however it also actually costs more than the Dynakitparts clone ST-35, or the DIYTube version from Triode or Uncle Ned (or at least very close in price).....
So I guess what I'm asking is (and can assume the answer), Do these things hold a candle to an ST-35 in sound quality ??? Are the tubes they utilize known as classic audio outputs (?) or are they more like the TV "plinkers" used in the K-501 types ?
I like my little "sweet16" pair of K-501's and they are great learning tools and tons of fun to modify, etc....But I did also build an ST-35 and am still in awe of its sonics, so it would all be another excercise in fun for me, but arent these new kits, with upgraded OPT's (at least the 16 watt versions) competing with an ST-35, perhaps for someone who is trying to decide what to build ????
What do You folks think ?? How good are the new S-5 kits, especially the 16 watt versions ???
And, if a 1620 OPT is suitable for these, and they're UL friendly, would'nt a clone or original Z-565 work as well.?
Just looking for Your thoughts - thanks
Russ

[jduffy]

I've been doing the same thing with a bunch of different amp ideas. Crunching the numbers to see what seems like the best amp for the money.

Or as we'd say back home, more holler for the dollar.

If anybody would like to chime in here, I'd be interested in your thoughts as well.

[chrx]

use some WIMA box caps, IIRC, the 0.15 uF/400V red "box" caps

I am a newbie and have just completed a K-501 mono amp (mono version of the K-502) - my first project of this kind. I installed .22uf orange drops in place of the original .22uf caps in the kit. What difference can one expect in going to a .15uf, from a .22uf, in this case?

Thank you,
chrx