A 6Y6 Push Pull amplifier

[Mosquito]

Hi
Thanks to Jazbo, that provided a good model of the 6Y6 power tetrode, I'm working on a circuit for this tube (I have a bunch of these, and want to put 'em to good use).
Nevertheless, while I found 3K PP is the best load for a clean 13W / 8 Ohm out, a 5K load gives a better THD figure at 1W.
On the contrary, at the onset of clipping (10.5V rms over 8 ohm load), the 3K load is way better (0.56% THD against 1.8%THD). I confess I can't understand if this is a simulation error, or is normal tube behaviour for the chosen operating points...?
Any ideas?

 

[Mosquito]

6Y6 LTSpice model

http://www.diyaudio.com/forums/tubes-valves/243950-vacuum-tube-spice-models-106.html#post4550699

 

[artosalo]

Used load resistance reflects to anode current of output tubes.
Have you verified that 150 V is optimum supply voltage for screen grids ? Actual Ug2 is only some 125 V (at the cathode is about 25 V).
Have you tried higher Ug2 values ?

 

[Frankel]

This appears to be normal tube behavior, and the simulation is showing it.

 

[Mosquito]

Have you tried higher Ug2 values ?

No, I chose to follow the manufacturer spec sheet, but I can try...

 

[artosalo]

When you are only simulating, don't worry about exceeding any specs.
So you can get experience about the effect of various parameters.

 

[Mosquito]

When you are only simulating, don't worry about exceeding any specs.
So you can get experience about the effect of various parameters.

Ok then, 300V on the plate, 200V at G2, and 5K plate to plate at 65% of maximun diss, give a wooping clean 20watt out, but it remain to be seen if the real tube can handle this...

 

[jlangholzj]

Ok then, 300V on the plate, 200V at G2, and 5K plate to plate at 65% of maximun diss, give a wooping clean 20watt out, but it remain to be seen if the real tube can handle this...

I've read of multiple guys running 6y6's up around 300V plate. Came across that when I was doing some research on the 6x6 family of tubes. I know the y's are only rated at 200 or so but its doable, especially if you're under P,diss. I've not actually done this myself so take it with a grain of salt. Just make sure your screen dissipation is below what it's rated at and you should be alright, I've heard that's where they'll typically give up the ghost.

 

[artosalo]

I don't see any problem with those voltages if dissipation is only 65 % of maximum.

 

[Mosquito]

Well, I ordered a custom OT with primary 35W, 5K PP and 3K derivations, to try all this on the bench.
On the other side, filament transformer need to stand to four tubes each one drawing 1.25A. a >30W unit , I guess...

 

[Mosquito]

Many thanks Artosalo, Frankel and jlangholzj for the assistance and good advice. It will be fun to try different types of 6Y6 in this project. I've got GE ST bottles, RCA GT, and JAN Phillips smaller glass ones.
The spec busting circuit as suggested by artosalo:

 

[Diego Zordan]

Hi! I have a 10w 5k plate to plate output transformer and two NOS 6Y6, what is the best voltage in plate and screen for those values? Thanks!!

 

[PRR]

At 10KCT load, you may as well set plate-cathode up near 20V, but keep G2 down to 100V-125V. Expect G1 bias near -14V. So 220V of B+ with 150r to 125r common cathode bias, and a pair of 4700r 5W resistors, bypassed, to set G2 voltage.