gofar99 wrote:
For all you folks who abstain from DC heaters these amps use AC.
HT Performance wrote:
I´m also using AC heaters on my EL34 Oddwatt. It´s amazing how it sounds. There is absolutely no hum at all!
HI.
I agree provided the AC supply is done
properly.Like my
Dynaco ST-70 also used AC heaters supply. Twisting pairs of wires to the tube heaters go without saying.
What I installed addtionally something crucial is a common mode AC noise filter to heater group of EACH channel. The AC noise filtler comprised 1
bifilar handwound coil on a small wooden form & an
AC film filter bridging the O/P leads of the coil. Bifilar winding is a must for any common mode noise filter.
Since the AC current is pretty large to go thru the coil, so the magnet wire used to wind the coil should not be too small. I used AWG #18, something I got in my part bin. The 2 small wooden forms were I DIY 'handcrafted' to size to fit the already very conjected space available underneath the metal chassis of the power amp.
Length of the manget wire is custom cut to provide only a small faction of a volt in order not to offset the required 6.3V heater voltage.
I need to install such RFI noise filter as the tube heaters in my phonostages are DC cells powered rechargeable by a SMPS which may emit RFI noises to the power amps. Besides common mode helps to cut down hum noise going thru the heaters.
c-J
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Calculated output power is 40 watts RMS (sounds like it too). I have done only minimal testing of them and will do more in the tweaking process. I will post a schematic when I am comfortable that they work up to my personal standards. My initial thoughts are they are quite quiet, low distortion, full power bandwidth (like all the other Oddwatts), good sound stage and imaging. Basically like all the others in the family just bigger. The B+ is 405 at 280 ma right now, but I believe that 450 at 300 ma is a reasonable target. Since the cathodes are about 37-39 volts above ground, this will result in total dissipation of about 120 watts it may be a bit close to max. 
Right now it is 102 watts and this may actually be better for the long run. I am still juggling with the load impedance to find the best match and a few other things. The driver is a 12AX7 SRPP. As this is a class A1 U/L mode there is no grid current during normal operation so there is no need for a hefty driver. For all you folks who abstain from DC heaters these amps use AC. It seems to reduce the S/N a bit, but until I run tests it is hard to say if it is significant. One thing for sure.... the KT120s are really huge by normal standards and look super. 
. Looks like you could get about 480V B+ with a SS Bridge. According to PSU Designer. I was thinking about a 180V transformer, not 360V.