S5 k-12g New Build Questions

[ghan]

Hey guys looking to buid my first tube amp.

A good friend recommended the k-12g from s5 electronics. (http://store.tubedepot.com/diy-k12g.html)

Any thoughts on this? How does this amp perform for the price, and is it easy to upgrade in the future if I decide to?

Any other suggestions? I have little soldering experience and I'm looking for a relatively easy build to start out with to get my feet wet.

Thanks!!

 

[skynet]

my suggestions go with magnavox 9302 tube amp

start by changing caps and resistor

ask question when you run in to problem everyone on AK can help

 

[ferninando]

ditto on the magnavox.
like this one.
super easy to work on and modify.
parts available ,cheep.
Sound fantastic too.

 

[Shadowdog]

The problem with the S-5 uses non std tubes not in production which will be hard to find down the road , also the Output Transformers which you will want to upgrade, and finally only 8W/CH.

You will spend this much in the end and still won't have the sonics or power of 17W/CH of a Dynaco ST-35 clone. diytube.com originated the PCB that allows lots of common tube rolling and Triode Electronics sells board kits and transformers.

If you diy chassis or buy the SS one later you might be able to do it for $350-400 Especially if you can find a rough condition plentiful Dynaco SCA-35 for it's iron (transformers) which the ST-35 also used.

Another option is tubelab.com for it's EL-84 PP amp PCB board & parts for $100 and you pick the quality of the OPT's (Output Transformers).

He also sell's a PCB for a great affordable SE amp with up to 10-12W/CH if you want to try SE (Single Ended) . Lot's of people love SE so that may be worth a look at also! He has a form @ diyaudio and there is lot's of support there.

Anyway save up for something with Great Output Transformers as that's defines the sound quality on your tube amp.

Do lot's of reading & don't rush in deciding. You will save $ in the long run!

Good luck!

Randy

 

[RamblinE]

I would recommend the K12G. It's not much money. The instructions are step by step, so it's hard to mess up. You don't need to know how to solder that well and you don't need to know how to read a schematic either. Further more 8wpc channel isn't as low as it sounds. What kind of setup would you use the amp in? How efficient are your speakers? I used it as a computer stereo for two years and it had more than enough power for near-field listening on my computer desk.

 

[ghan]

Thanks for the tips. If I were to go the 9302 route, where is the best place to pick one up? I did a quick eBay and CL search and wasn't able to find any...

How much more difficult is it to refurb an old unit vs building from scratch?

Sound will come from computer or iPod. I don't have speakers yet, I'm still debating on building a set for myself, or buys something used. The idea of building my own speakers is intriguing.

 

[skynet]

for ebay search vintage magnavox
for CL search magnavox console

if you can found a console on CL, the magnavox console will come the speaker and horn.

 

[RamblinE]

The problem with a vintage suggestion is that good examples are not always one hundred percent available. It could possibly take much longer to get one up and running than it would take the K12G whose build time I clocked at around six hours (having never soldered before). While it's true that it's not perfect (the amount of hum the transformers introduce becomes very evident when you try to use it on low impedance headphones; I have to resolder the tube sockets because of my original sloppy work) it's an entry level tube kit of unbeatable value. A lot of cheap tube offerings you might see on DIY Audio, Head-fi and Ebay employ tube buffers on mosfets or other solid state. The K12G is purely a tubed unit with the exception of a solid state power rectifyer. Here's a sweet gallery of what other builders have done with the kit http://diyaudioprojects.com/Gallery/thumbnails.php?album=11&page=3 I just built it as it appears in the stock photo on S5's site.

 

[Shadowdog]

The Two PP EL84/6BQ5 amps I mentioned are strictly tube also so very simple to build & service . They will give you amazing sonics with no hum also.

Another thing is it's hard to beat the sonics of EL84/6BQ5 tubes! Most everybody will agree with that. You do need efficient (90 + dB with at least 95-96+) the best) speakers with 15-17W/CH to get the best in sonics though. As mentioned near field listening or a small room is good with not so efficient speakers. I've got to build some efficient speakers someday myself! Tube watts do seem to be pretty robust because they don't distort badly near the limit like SS and are easier on the ears to me anyway.

The Only SS parts are the diodes in the PS for the rectifier on the ST-35 which is simpler & less costly than a rect. tube.

Some builders building there own chassis add the common in production 5AR4/GZ34 as they want all tubes. It can help to have the tube as it slowly ramps up the B+ making it easier on the rest of the tubes.

You can use ICL (In rush current limiters) to pretty much do the same thing. Most high power amps use SS rectifiers as the rect. tubes are more stressed on a bigger amp.

Another bonus with SS diodes in the PS is the bass can be improved because more capacitance can be added in the PS before the B+.

There is however one really nice mod for many PP amps with easy to drive output tubes like the EL84/6V6/7591 types that converts the amp to fixed bias with a small inexpensive negative SS voltage regulator and that is Dave Gillespie's EFB mod.

It increases output tube life, improves the sonics, and adds 2-3 W/CH. all for $10-20.
It is a simple circuit can be added later when you have some experience. See improved SCA/ST-35 performance under the ST-35 form on the diytube.com site.

Sometimes it's quicker to build new if you have a built chassis already than replace parts on some hard to work on vintage pieces.

Anyway notice the size of the Dynaco SCA/ST-35 Z-565 output transformers which are highly regarded and will give you a full 20-20 KHZ at full power because of their extra interleaving and size, beating many other similar transformers and for sure the smaller ones. They also have UL taps which is a bonus to many. Well worth saving up for!


Randy

 

[ghan]

Thanks Randy. I've previously looked at the boards from tubelab, and I think I strayed away because they were not complete kits, and required me to piece together everything I needed.

I'm all for spending a little more money now for something that will last longer but I want to make sure I'm not getting in over my head.

 

[ghan]

Randy,

Are you referring to the Simple SE from tubelab or the Simple PP

 

[Shadowdog]

The Simple PP as it has 15-17W/CH & it looks like you were looking for PP , plus you can get it with a kit of parts except for the tubes and transformers so not hard to put together. It's a similar circuit to the one used on the Dynaco ST-35 also so will have similar power. You can add a volume control to it just like on the Dynaco ST-35 also.

I mentioned the Simple SE in case you were interested. As you mentioned you would have to get the parts for the PCB though. If you were interested in that amp you could ask George as he had mentioned a while ago he had most of the parts & was missing a PS cap or two. He did have part #'s listed though so you could get all the parts except the tubes & iron from one vendor. The present economy may have hurt that though!

If you want a nice P2P wired SE amp kit with similar power to the Simple SE in a full kit or without the transformers & tubes, scott17 has a form under the vendors @ diyaudio. It is a strictly tube amp with a very popular circuit out on the Forms amongst the diy crowd and comes with great instructions so anybody could assemble it. Probably out of your budget though @ close to $820 last I saw for the full kit, but has top notch parts. He had dropped the price from $900 maybe temporarily.

Hope that helps!

Randy

 

[ghan]

Thanks! I think you have convinced me to go with the simple se. After looking at DIYaudio there are quite a few newbs like me who have been able to successfully build the amp.

I just need to decide on the tubes and iron. Any recommendations?

 

[ferninando]

try 'magnavox tube amp,amplifier'. there are several now on ebay.

 

[Shadowdog]

The only SE amp I listened to was through a CD player plugged into the RCA input on my late 1940's RCA AM/FM table radio and it had a great nice midrange, and you could listen to it for hrs without fatigue. I imagine a better output transformer and a full range speaker would extend the bandwidth greatly.
It had a 6V6 output tube , but you only get 2W, so many go for a bigger PS trans. for a higher B+ which you need for the higher power bigger tubes.

Just from reading I don't think the EL34 would be my choice as it looks to me from my reading that the highs and lows tend to be rolled off and it has more distortion than I would like. Maybe on the lower price end the 6L6 might be what I would try, with the KT-88 on the high end. You would have the highest power potential with the KT-88 also.

PS transformers as you have gathered depend on the Output Tubes. George lists some that he used. Others have used Edcor.

Output transformers depend on the budget as the bigger usually have sonic advantages , but are costlier. Edcor looks to be popular on the low priced end with the 15W GX series the lowest I would go with the big 25W CX ones maybe a nice choice.
The bigger one will certainly give a more bass, but maybe not highs.

He mentions the Transcendars (He sells on Ebay & has a web site) as his next choice with Electraprints at the top.

He never tried the sometimes pricey overseas brands that can be great also.

Anyway the Edcors have UL taps which you want with his circuit as an option, and you should make sure any other brand you pick has them.

He seems to prefer a 5K primary for the transformers which is a good compromise between power and sonics. You can use 3-3.5K , for a bit more power, but you get a little more distortion.

Sure lots of reading out there on choices for SE or SET Output Transformers & favourites.

Sometimes you can pick up a good pair of used OPT's for a great price on AK, diyaudio, AA (audioasylum), canuckaudio etc. also.

Hope that helps!

Randy