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mpleasant 12th March 2011 12:33 AM

K-16ls + ton pcb (just finished pics)
Hi everyone, since im new here i will take this time to introduce my self, i am an electronics engineer and have loved music and amplifiers since as long as i can remember and every type of media music can be stored on.

Here's my story of how i came to posses a k-16ls tube kit, it all started about 5 years ago when i bought a pye cambrige table top valve radio from a junk store (not working) with every intention to fix it but alas my experience ends with ghettoblasters and solid state hi fi as i collect and repair these.

so the radio got shelved, but recently about 4 months ago i met someone through work who explained how valves work and this made me want to try and fix that old radio, so i tried and after a lot of time and "borrowing" parts from work i got it going (did not sound good) after a while fixed all the issues and was so impressed by the almost HD like sound that i wanted an amp in stereo so i got looking and found this kit (wanted all valve i did see the hybrid docks etc) from s5 electrinics (the shock of the import tax nearly gave me a heart attack when it arrived).

so i assembled it on the supplied wood and fired it up (took about 2 hours to built the main kit and tone board) no issues and it sounded lovely out of the kit so to speak.

then i decided to case it, see pics i built this case myself from mdf and tin the only part i cant claim rights to is the top which was taken from an old vcr.

so you can see the case i built, i also included a fan for cooling near the transformer and since these pics were taken i have laser engraved some plates of polished tin for volume bass and id etc, also i have rerouted all cables for line sockets the opposite way round the chassis to the mains to help remove hum and also grounded the rca sockets, hum seems to have gone now and by grounding the tin cage to earth it acts like a farady cage protecting against interferance.

really the only things i wanted to ask were.... i hear many people change opts but i am trying to understand why because i seem to have a full bass response on my high sensitivity speakers so i dont see what i have to gain, and allso despite the fan my transformer still seems to get fairly warm is this normal.

are there any other things worth looking at i am very happy with the sound but a little more power would be nice, are there any substitute valves etc with more power output.

also last question, if i wanted to bridge this amp, am i correct in thinking that i would loop the left rca to the right one, and then reverse the output wires on the opt so one chanel is reversed phase, then connect one 8 ohm speaker to both reds to get a 4 ohm load?

thanks in advance sorry about the length hope you enjoyed reading and look forward to your answers.


mpleasant 13th March 2011 01:32 PM

so... nobody is interested in these kits? you know rome wasnt built in a day i have to start somewhere.....

SY 13th March 2011 01:57 PM


Originally Posted by mpleasant (
so... nobody is interested in these kits? you know rome wasnt built in a day i have to start somewhere.....

Nope, just hadn't seen it in the mad rush of posts yesterday. :D Push-pull parallel EL84 for the output stage?

Welcome to the forum- there really is some amazing tube knowledge on tap here, so keep at it!

mpleasant 13th March 2011 03:04 PM

so the el84 is an 8 pin valve so i guess that would require reworks of the pcb, and another 100v on the anode? ouch sounds like a lot of work for another 8w pch, but fun too:D

acmarsden 13th March 2011 04:01 PM

Congrats on your first build. I have been involved building three K-16LS kits (Son. Daughter, Neighbour). The valves used (6005 and 5670) appear to be very rugged - no failures yet (2+ years).

The easiest and probably best upgrade is to replace the dinky output transformers with more substantial iron. I used 5K PP OPT's from DIYHiFiSupply and from Hammond to great effect, especially on the frequency extremes.

The K-16LS is a great learners kit and very good value for money. Lots of tweaks available on the web.

mpleasant 13th March 2011 04:42 PM

i have to admit i have been considering the upgrade on opts, but if i balance the cost vs sound, i am a rock music fan so subsonic bass is not too relavent to me and as far as i can tell the standards are driving my speakers ok as they are fairly effecient speakers, but given they have 15" woofers they dont need driving hard to get good bass extention, but if someone were selling some secondhand opt's in the uk at a good price i might consider it, i dont intend to mod this kit too much apart from opts and maybe a better transformer for higher HT as i want it to be simple to fix if something fails.

i will build another more refined amp using PP wireing when i decide what to use, i want something with more power in stereo but with a simple schematic and common valves, my idea was to use a 110.110 - 110.110 transformer so i can use the 240 on from mains and the 220 rms dc from each output for HT with a seperate heater tranny.

so any schematics would be good im thinking PP for the power i want.

Eli Duttman 13th March 2011 05:50 PM


also last question, if i wanted to bridge this amp, am i correct in thinking that i would loop the left rca to the right one, and then reverse the output wires on the opt so one chanel is reversed phase, then connect one 8 ohm speaker to both reds to get a 4 ohm load?

No go! You're ignoring the NFB circuitry and common ground of the 2 sections. If the O/P trafo secondaries floated (they don't) you could wire the I/Ps in parallel and the speaker O/Ps in series.

To strap the unit into a monoblock, you need to drive the I/Ps with a pair of 180o out of phase signals. You take the speaker O/P from the "hot" connections of both sections. Each section "sees" only 1/2 of the load. So, 8 Ω speakers get connected to 4 Ω taps. Since 2 Ω speaker taps are not present on the O/P "iron", 4 Ω speakers can't be used with the strapped amp.


As for more power, the 7 pin 6005/6AQ5W and the 9 pin (Noval) EL84/6BQ5 are both "12" W. plate dissipation types. So, I see no future in that sort of swap. If you want to keep the existing small signal circuitry, you can walk in the steps of Fisher, Scott, et al, and use 7591 family O/P tubes. Those venerable manufacturers took full advantage of the fact that circuitry that works with "12" W. types also works with the 7591 family. The EL34/6CA7 requires a larger drive signal than 12 W. types and different small signal circuitry.

mpleasant 13th March 2011 06:03 PM

so are you saying that if i swap my o/p tubes for 7591 i would not need make any changes to existing pin wiring or am i grabbing the wrong end of a hot stick!

i guess an increase in HT voltage would be necasary and also bigger opts to handle the extra power.

also im still struggling to grasp the concept of a "matched pair" from what i can see of the k-16ls kit they use 4 6005 pch and 2 pairs are reverse phase the others are parallel so does the k-16ls employ a matched quad?

Eli Duttman 13th March 2011 09:18 PM

Things are never as simple as one would wish. :( I did some digging and it turns out the amp is Class "A" push/pull/parallel. Class "A" tends to sound good, but it's inefficient. Drive voltage requirements are comparatively modest. Look at the 6005 data sheet. The 4X 6005 O/P tubes (valves) in each channel should be closely matched, a quad. Proper matching requires that culling of specimens be done to select tubes whose cathode current and transconductance (gm) measure nearly the same. Its really not different than selecting BJTs for matching β.

There's no way you can modify that PCB to use more capable (power wise) tubes, as the bottles are larger in diameter and the buggers are packed in tight. Think about another build employing better "iron" and Class "AB" O/P tubes. As can be seen from the data sheet, a pair of 7591s can comfortably yield 30+ W. Since this is "a clean sheet of paper", circuitry employing the EL34 and 6L6 families should be considered too.

Costs escalate quickly in tandem with rising O/P power. "Iron" expense is the driving factor. The tube you can easily squeeze out 60 W./pair is the KT88. Can your bank balance stand the "hit"?

mpleasant 13th March 2011 09:29 PM

yeah i see where you are coming from, im listing to the amp now and that thunderous bass i get from my sky scream speakers is great but the distortion comes in quickly past 12 oclock with the bass gain set at 3 oclock and if its not the speakers distorting (doubtfull since these are used for rave systems with slight modification to the crossover) then it must be the valves running out of poke, strange though because if i cut the bass and trebble proportionately i can get more volume and the distortion comes in later?

with regard to matching i never matched the included valves and unless i did something very wrong when i opened the package they were all jumbled up in packs of six, so would matching help me obtain less distortion at high volume, if yes how can i do it with basic tools, ie fluke scope/meter etc.

also with regard to the high power opts i work in a company that has a winder i would just need the specs and cores etc.

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