6s4a Clementine.....Sick Thought

[zippy1540]

Just having sick thoughts about building a clementine using 6sl7 input and 6s4a output. I know it would take some power supply modifications along with some component changes for the output section. Anyone think this is worth while or am i wasting my time? I have about 30 or so 6s4a's. i tried them in a decware clone i built a while ago and they didn't sound too bad.

[Geek]

Nononono.... a sick thought would be transistor outputs

Cheers!

[zippy1540]

Ewwwwwwww javascript:emoticon('(sick)')

[EWBrown]

I've had good results with 6S4As, use a B+ around 325V, plate / cathode current of 25 mA, Rk should be 390-400 ohms, 2W, bypassed with 100 uF / 35V caps. This is the "magic sweet spot" for these tubes.

OPT primary impedance needs to be 10 to 12K ohms, in order to play well and sound best with the fairly high (3700 ohms) internal plate resistance of these triodes..

Run them in parallel PSET, then a 5-6K primary OPT would work well, and deliver 2X the power.

HTH

/ed B in NC

[zippy1540]

Thank you, those are the numbers i was looking for. I happen to have a set of output transformers from an organ that measure out to 40-1 which shows 12800 into an 8 ohm load if i remember the math correctly. What would my power output be with this transformer and setup? what is the formula to figure it out?

[EWBrown]

With 6S4As, and the 12.8K:8 OPTs, I'll SWAG about 1 to1.5 WPC, I can run the curves the old fashioned way (with pencil and papler) and see what results I get from that.

Typically the max power output is about 20% of the actual plate dissipation ((V P-K) X (IP)), the 6S4 is good for 8.5W PD max, under the actual conditions, it runs around 7.5W, and 20% of that would be 1.5W.
The 1626 is good for about 750mW.

HTH

/ed B

[zippy1540]

Prototype is coming along. Going to have to try a different power transformer since i cannot get 325vdc filtered enough. It's a scrap box XFMR. i am getting about 310v for the B+. initial impressions, it's really quiet but the gain seems lacking. my voltage at pins 2/5 on the 6sl7 is about 170, gotta get that down a bit. i'm using the clementine schematic just changed the output tube to 6s4a with as close to the proper voltage as i can get. Time to play around some more.

[zippy1540]

Getting closer, B+ is 315v, pin 2/5 on 6sl7 is at 129v. My volume pot is noisy so i have to replace it and add some speaker jacks then it's ready to bring into the house for a real test. so far on the garage speakers it sounds really clear and dynamic. I'll report back once i can hear it in the house from a good source.

[EWBrown]

325 VDC isn't an absolute, anything from 300 to 330VDC is fine. I just hit on 325VDC because that is what I got out of the power trannie and filter components that I used in a couple of 6S4A SET builds.

310 or 315VDC is more than good enough, the difference is less than 5% under 325V.

/ed B

[zippy1540]

So i took it over to a friends house to hear it on his klipsh corner horns and cornwall 2's and i cannot seem to get him to let go of it. says it beats out any amp he's had hooked up so far except it's lacking the ear bleeding power. not a big suprise with only 1.5W. once i get it back i'll put the prototype in a reasonable chassis. he likes it the way it is but i have problems with completely exposed B rail voltages.

[battradio]

What are you using for output transformers .

[zippy1540]

some old scavanged transformers that ran 6aq5's. measured out to 40-1 so with 8ohm i'm reflecting 12.8k to the 6s4a's. The amp is dead quiet and the sound is amazingly full.

[zippy1540]

Here it is in a new chassis, listening to it now. My best sounding amp so far. Full deep bass, sparkling highs, really clear imaging through my hand built metronome speakers and budgie pre-amp.

http://i920.photobucket.com/albums/ad47 ... 21935a.jpg

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[EWBrown]

Nice amp! Looks and sounds great!

6S4As are a much under-appreciated, and truly great sounding tube.

/ed B

[zippy1540]

Thank you, i agree these 6s4a's are really good sounding tubes. since i have about 40 of the 6s4a's i was thinking my next step might be 3 per channel in PSE for about 4.5W. I'm not sure what issues i might run into with that or if i should just buy some EL-34's and run those.