6ck4 sweetspot

[Klimon]

Hi,

I'm looking for suggestions on good bias spot for 6ck4 in SE. Been running such an amp for a while but it's time to look for better sounding spots; currently running at 250V/43ma 550ohms Rcathode, 5k Zout which sounds a little thin; before it had about 270v on the plate with same Rcathode which sounded great, much warmer. I know some of you have toyed with the 6ck4, suggestions are most welcome!!

Simon

[sorenj07]

here's a schematic i had in my bookmarks, might give you some more ideas

http://www.kta-hifi.net/projects/amp...4amp/6CK4.html

[andyjevans]

I dn't know if this is useful information, but I started off with a 6CK4 output PP amp and when I substituted 6AH4 tubes it was considerably better, specially in the treble. I believe I ran it with about 390v HT and self biased.

[Sheldon]

I like mine, with similar plate conditions, but with an 8k transformer.

Sheldon

[Miles Prower]

Originally posted by Klimon
I'm looking for suggestions on good bias spot for 6ck4 in SE.

Unforch, there really isn't one. The 6CK4 works better as a push-pull than a single ended amp.

Here's a pretty good PP loadline. The h3 estimate comes in at 3.7%, which is not good and not bad. The actual h3 will be considerably less since the graphical estimation method comes in high, due to the simplifying assumptions needed to make it work at all. (I used the same method to estimate h3 for the 6BQ6 and the actual measured h3 was almost half of the estimate.) This just might be OK. Of course, there is no indication as to what it does with higher order harmonics. Even though there are graphical methods, it'd be quicker to breadboard the thing and measure directly. As for what it sounds like, I dunnow. Different VTs (triodes and pentodes alike) have their own "sonic personalities" depending on whether or not they generate those dissonant high order harmonics, which, in turn, determines how you use corrective feedback.

I almost did a 6CK4 project, but had the OPT and power xfmr, and a lot of other junk box pickin's for a 6BQ6 amp instead, so that's what I did.

There are lots better triodes out there for SE use than this one.

[Klimon]

Thanks for your remarks gentlemen. 30mA / 10w is a welcome guideline (I can't seem to open the pdf though); I'll experiment and listen a little to see what I like best --- I do believe 6ck4 has alot of potential in SE; sounded really sweet before I messed things up by implementing the loadline that looked good on paper.

Simon

[kevinkr]

I've run them as high as 330V at 30mA and around 275V @ 35 - 40mA or so in SE (as a driver) with pretty good results. Not all 6CK4 are good, I tend to prefer the Sylvanias with the box plate with wings from the center of the plate structure on either side.. The narrow ends have three perforations and you can see the grid support rods. IMO The best sounding ones have grey plates, not the black shown here.

[G]

Originally posted by Miles Prower
There are lots better triodes out there for SE use than this one.

Cheap ones? Please do tell. I have a pair of Magnaquest RH40 transformers with 5K primaries that are burning a hole in their box!

[Miles Prower]

^^^^
None of these are especially "cheap". As for other types, the 6AH4GT comes to mind, as does the 6BX7. The Unit 2 of the 6EW7 dissimilar dual triode looks pretty 2A3-ish.

Jack at Electraprint has some 6BX7 designs. Here's an article on a 6AH4 project that would be a better fit for that 5K OPT than would a 6CK4.

The 6AH4 just might be your best bet here.

[Geek]

Hi,

Once you hear the "perfect watt" of a 6AH4, anything else will be difficult to tolerate, especially on that top end

I also did find the 6EW7 and 6FD7 being superb into 5K loads. The latter being a pretty smokin' efficient at 25%+

Cheers!