What is “that” in twice that? Could you elaborate/explain “With 40% UL plates should go down to 100V in AB1” please.
This is very low and keeps the loadline of the phase splitter quite flat.
Do you have a scope to check the ac voltages at phase splitter anodes, after the powerdrive and on the output transformer?
Sure! Here it is the loadline with B+ = 385V, Ia = 45 ma and Raa 4 kOhm.
I've highlighted the value with g1 = 0 V, that is with plate at 105V.
Swinging from 385 to 105V (and mirrored on the other side as well) in a push pull with 4 k Raa will give [2 x (385-105) / sqrt(2)]^2 / 4000 = 40 Wrms circa.
I've not considered the triodizing effect of the local shunt feedback on the tubes, but it was just to say that the power should be significantly higher.
I've just noticed he uses KT77. This changes things a bit: swinging down to 126 V gives around 33 Wrms in AB1.
Same power but better response should be given by a 6.6 kOhm Raa:
Please note that the Pa here is set at 32 W for the KT77, but as far as I know, current production is 25 W like EL34.
All plots are not considering the triodizing effect of the local feedback, just the UL effect.
Same power but better response should be given by a 6.6 kOhm Raa:
Please note that the Pa here is set at 32 W for the KT77, but as far as I know, current production is 25 W like EL34.
All plots are not considering the triodizing effect of the local feedback, just the UL effect.
I think I possibly found something. It looks like the signal is clipped before it reaches the output tubes. The yellow channel is measured just after R11/R12 and the purple is measured at the output over the 8R dummy resistors. What should I check next?
Btw. I tried to change the shunt feedback resistor to 39K (I just removed a parallel resistor). I didn't make any difference to the clipping. I lowed the value because of advice earlier in this thread (although I can't say I heard any difference.)
Please scope the voltage on R7 and R8 to see if it is due to the phase splitter or the powerdrive.
Thanks! I'm not exactly sure what you ask me to do, but I connected to probe to one side of R7 as in the photo at the bottom and I got this. I'm reasonably good at building stuff, but my knowledge about electronics is limited (but ask me about darkroom work and film photography...).
If this is the wrong way to do it, please let me know. I am of course very grateful for all the help I'm getting here.
If this is the wrong way to do it, please let me know. I am of course very grateful for all the help I'm getting here.
What is the highest voltage of the yellow line here? It seems asymmetric, so I would like to understand why.
The issue could be on the phase splitter or due to the powerdrive (the mosfets after the phase splitter).
The issue could be on the phase splitter or due to the powerdrive (the mosfets after the phase splitter).
I'll make more measurements later tonight.
But I've been wondering. Since I built the amplifier according to the boards, schematics and parts list from this group buy:
https://www.diyaudio.com/community/threads/gb-el34-baby-huey-amp-and-psu-mk2-pcb.368190/
Has anyone else built the amplifier with the same parts and did they end up with a perfectly working amplifier or has someone experienced the same problem?
But I've been wondering. Since I built the amplifier according to the boards, schematics and parts list from this group buy:
https://www.diyaudio.com/community/threads/gb-el34-baby-huey-amp-and-psu-mk2-pcb.368190/
Has anyone else built the amplifier with the same parts and did they end up with a perfectly working amplifier or has someone experienced the same problem?
It swings from -38 to +31V clipped?
This would mean that the bias voltage is almost 0 V, but BH is fixed bias.
This would mean that the bias voltage is almost 0 V, but BH is fixed bias.
There were some power supply mods that had to be done to get the PSU board working correctly, including swapping leads on a FET IIRC.
What this project needs is someone to launch BH EL34 v2, consolidating the modifications, and start a new thread. Some of these designs are strangled by the effort it takes to determine the current state of play.
What this project needs is someone to launch BH EL34 v2, consolidating the modifications, and start a new thread. Some of these designs are strangled by the effort it takes to determine the current state of play.
Bias voltage was about -25 V when I measured. Anyway, the negative voltage supply is at least in a better state now. I don't understand what the issue with the power output might be, so I've decided to leave it for another day and put the amplifier back into service. The amplifier sounds great, so there is that.
The main differences are the one ointed out by Gingertube relating to the PSU ...
psu mods
I had this one ... (post #967)
LM555 timer delay. I use the 33uF that is on the screen printing on the PSU board, and with the 2.2M resistor that gives 72s delay (actually 82s when I timed it). In the BOM it is stated as 10uF, and that would be a more reasonable 30 odd seconds. (Or is switching the resistor value the best strategy?)
I don't think there are that many. Has the Wiki functionality been removed from DiyAudio? There used to be some useful stuff there, too.
psu mods
I had this one ... (post #967)
LM555 timer delay. I use the 33uF that is on the screen printing on the PSU board, and with the 2.2M resistor that gives 72s delay (actually 82s when I timed it). In the BOM it is stated as 10uF, and that would be a more reasonable 30 odd seconds. (Or is switching the resistor value the best strategy?)
I don't think there are that many. Has the Wiki functionality been removed from DiyAudio? There used to be some useful stuff there, too.
That’s what I had tried to do whilst developing my PCB for a stereo build, detailed here. It incorporates the main tweaks / corrections mentioned - and can be further modified should people wish by taking the source files and doing as people please…
I‘ve been using my BH daily since March. Sounds great but likely needs re-balancing / biasing. Just haven’t had the time.
What is the voltage, UL%, loadline and local feedback most used with BH EL34? 400V, 40% UL, around 4k Raa and 47k+39k+47k?
I've used mine with 450V, 23%UL, 6.6k Raa and 47k+33k+47k. Also with 40%UL and 7k Raa, everything else being the same.
Having a higher B+, I've raised the phase splitter plate resistors to 270k for a flatter loadline so a bit more gain.
I've used mine with 450V, 23%UL, 6.6k Raa and 47k+33k+47k. Also with 40%UL and 7k Raa, everything else being the same.
Having a higher B+, I've raised the phase splitter plate resistors to 270k for a flatter loadline so a bit more gain.