Don't get me wrong, OPT transformer models are a bit of mine field, I agree.
THD is another area where LTSpice is indeed overly optimistic, as you pointed out.
I suspect if we were clever enough to add all the trace parasitics and had more accurate models, we would be closer. Even trying various different speaker models for the load. You may have an advantage there with the OPT as less load dependent.
First of all dosconnect the FB
Then, bypass the 6N6 so you have a better gain.
At this point check with the scope the clipping and read the voltage on secondary.
I can't see the real schematic; the connection is pentode
Can you post it?
Walter
Then, bypass the 6N6 so you have a better gain.
At this point check with the scope the clipping and read the voltage on secondary.
I can't see the real schematic; the connection is pentode
Can you post it?
Walter
disso,
Did you take jhstewart9's recommendation?
. . . He said to bypass R8, 2.2k with 100uF to ground (100uF, Screen to ground).
Please do that, and report the results.
The un-bypassed R8, 2.2k, causes degeneration (loss of gain, and loss of power).
Did you take jhstewart9's recommendation?
. . . He said to bypass R8, 2.2k with 100uF to ground (100uF, Screen to ground).
Please do that, and report the results.
The un-bypassed R8, 2.2k, causes degeneration (loss of gain, and loss of power).
Haven't had much time yesterday, what i did try was replacing R8 with 100R (like kevinkr and jhstewart9 suggested), that changed nothing. The supply voltage also did not sag, i have 150mA available from the SMPS so it should work out. I don't have a 100u/300V+ cap right now. The issue is that the driver is clipping first and drive voltage is insufficient so that's what i'll be looking at first.
I will try this now. the schematic in my first post is the real one, the 6P15 is pentode connected.
Also thanks to tvrgeek for the clarification and advice on the four command, seems i still have a lot to learn when it comes to ltspice.
Alright, tested disconnecting feedback and installing 100u bypass cap for the driver. Result is a lot more voltage swing on 6P15 grid, it's the output tube clipping first now.
However there is no additional power..
Also checked my box of caps again and found a 33u 450V one so i tried bypassing g2 of the 6P15 (using 100R resistor now) but that also didn't change anything.
However there is no additional power..
Also checked my box of caps again and found a 33u 450V one so i tried bypassing g2 of the 6P15 (using 100R resistor now) but that also didn't change anything.
it clips when voltage at the 6P15 grid is 1.9VRMS, the driver is far from clipping at that point. Measuring at the output that results in 3.8VRMS which is about 1.8W.
ah, sorry. yes it's symmetrical.
On another note: could this also be caused by the output transformers becoming saturated? I should probably have mentioned it, they are cheap chinese transformers, i bought them a long time ago so i can't find the specs anymore (no longer available on ebay). They were listed as being able to provide 5W with EL84's but it wouldn't be the first ebay part with overstated specs.
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Just in case no-one checked / asked: is the ratio of the output transformer correct and is the transformer functioning properly? E.g. you will not get the proper output voltage if you connect to a 4 Ohm tap thinking it is the 8 Ohm tap.
If the sticker that's on the ot is correct then i did connect my load to the 8 ohm tap but just to be safe i'll measure the transformer tomorrow.
Being a 5000:8 OPT, 3.8 Vrms on 8 Ohm should have 25 times that on the primary, so 95 Vrms, or 268 Vpp.
This means you bring the plate down to 66 V at full power, that seems reasonable.
How low the plate goes in your simulations?
So the transformer is wired correctly, i did connect my 8 ohm load to the 8 ohm tab.
I'm measuring something different here. Right before clipping the anode measures 346Vpp, 248Vrms. The plate swings down to 43V, that is pretty close to the simulated value. Current state of the circuit is 100µF bypass cap in driver cathode, R6 = 150, R5 = 10K, R8 = 100R, feedback disconnected.
There is a significant voltage drop across the OT primary that i didn't notice before. At full power B+ = 240V but Anode = 215V.
I'm measuring something different here. Right before clipping the anode measures 346Vpp, 248Vrms. The plate swings down to 43V, that is pretty close to the simulated value. Current state of the circuit is 100µF bypass cap in driver cathode, R6 = 150, R5 = 10K, R8 = 100R, feedback disconnected.
There is a significant voltage drop across the OT primary that i didn't notice before. At full power B+ = 240V but Anode = 215V.