Kerry

Thanks Craig for summarizing. Very glad you got everything working

I think it may be as simple as he can't post anymore without breaking Inu's wishes

Congrats Craig! Very excited to hear your impressions

What was the result? Did you end up with a digital scope. Reason is I was thinking of getting the 1052E as well. Also wanted to check what the max voltage is with the 10x probe. Thx.

Which of the K216's are you doing this too? Just the ones feeding the output stage (Q26, Q27) or are you also doing it to the ones feed the active battery (Q4, Q5)?

Yes, Thank You and Merry Christmas / Happy Holidays !

I think the 100V zener's job is to protect the J79's, which have a voltage rating of 200V. I'm guessing they did that, but would love to know for sure (on my premise and result). I'm not sure of all the root issues that could cause this to be triggered. Most everything is current limited so if we looked at most common failure points, then we could get to how much current & voltage the zeners would need to handle (without damaging the J79's) in a fail situation. At the end though, the zeners are pretty easy to replace so I wouldn't mind that too much. Seems like tube rolling with the wrong tube could be a likely fail situation. I'd love to get other thoughts... Also, I haven't addressed Marc's question of how do they die.

I'm guessing you are measuring the bias on the jack side of the 5M resistor. That makes sense since most meters are 10M ohms. If you calculate the potential divide it puts the bias at about 595V. Once you have the zeners swapped out, I'd be curious what the gates of Q4,5 are as well as the test points at R99, R101.

EDIT: Just saw deepak's post. Nevermind.

Looking forward to it. I'm really excited to get this going.

Nice job on the bulid Andy. It's always very thrilling to power up for the first time. Good luck and enjoy! I'm looking forward to getting this build moving I've got a reasonably good feeling for the circuit and once I have an inventory of parts I can start moving on pulling everything together.

Some more thoughts on the battery operation. I look at it as a high voltage op amp with inputs on the bases of Q16 / Q17 and the output feeding Q23. The resistor string R31 - R34 and RV1 forms a simple voltage divider so that on 740V RV1 will adjust the base of Q17 to the exact same voltage as the base of Q16. Q23 will then keep the output at 740V with the op amp controlling the voltage. The job of RV2 is to set a specific current against R42 which translates into a specific voltage feeding the base of Q17. So RV2 is there to adjust the current and ultimately the voltage so that it is in range of what RV1 can be adjusted to. In Kevin's KGSSHV power supply he replaced RV2, the FET, LEDs and R42 with a precise voltage reference of 10V, so the resistor string on the right is then recalculated to be able to adjust the output of RV1 to 10V against whatever voltage is required for the full resistor string. Pretty neat So, it seems that the issue of insufficient current feeding Q23 can be solved by changing the value of R39 (increasing the current output of the op amp) and then using a higher voltage part with a lower hFE is also possible. Seems good, but I would defer to Kevin on how that could impact the operation of the amp. I wouldn't presume to know the reality associated with this change.

It's coming alive! Very cool

The models I used where Duncan Amps for the tubes and the transistors were scavenged from the internet. I can't say that they are perfect (I'm guessing the hFEs are not corrrect), but they did simulate the volages right on with Kevin's schematic. I had to tweak an LED model to produce 1.872V which gave the correct currrents. I've got a question on the load lines/DC operating points for the tubes on the input stage. I sat with the Mogan Jones book last night and was trying to calculate out the Vgk values for the tubes. They seem to be arranged as a Cascode with current sources/sinks. The spice model shows -2.2V for the upper tubes and just under -1V for the lower tubes. As best as I can understand it, you subtract the anode voltage of the bottom tube (approximately 70.2V) from the HT (250V) giving about 180V. The operating point for these tubes is about 50V down from the HT so that would set it at 130V for purposes of determining the operating point. Because there is a current source above the tubes, I plotted 130V against 5mA on the Plate Characteristics graph and came up with about -3.5V for Vgk. This is pretty different from the spice model. For the bottom tubes I took the anode voltage (approximately 70) and plotted it on the triode transfer characteristics graph at 5mA and came up with approximately -1.85. Again the model suggested just under 1V, which jives with Kevin's schematic, which it shows the grids at about 1V against a 0VDC input. Either the models are incorrect (very possible) or I've done the math wrong (very possible). Any thoughts?

Craig - I modeled the active battery in LTSpice to confirm some numbers. If you adjust RV2 so that the voltage on the base of Q16 is higher (i used 7.489V relative to the collector). You should still be in range with RV1 to get the 740V, but you need to set it towards R33 (see schematic). That will put the current through R39 at about 112uA, only marginally better. http://img696.imageshack.us/img696/3682/activebatteryspice.gif If you want the model, let me know.

Looking good.

The top is blue. I've got the components mounted on top, but the rail transistors mount on the bottom along with the filament transformer. I needed it this way for how I wanted to mount it.

Nice idea. Thanks for the input.

Here's the pics of the BH power supply based on the HV supply here:

I thought that this was published already. I don't have the ability to take this down anymore.

For fun I've been playing with the HV power supply. I've modified it to work with the Blue Hawaii at +/-400V. I'm posting here since I first started playing with it in thread. Now that I understand the design, I think it's really very slick. Here's the rough schematic and board layout. The board is 12" wide and designed with the heat producing sand to sit on the chassis' heatsinks. images removed by request of Kerry

Hi Kevin, There is a new version of this coming out that looks pretty cool. Has two channels and will support 800V with the 10x probe. I think it also has a built in function generator. If you think it was worth it for the $43 version I may just try this $179. Pre-Order

They have a really nice selection. I had a local lumber yard that was nice because you could look and feel the wood. Also, they could plane the wood for me to any thickness - great for speakers.

Sweet!

Nice job on this Craig. This really makes it easier to understand the circuit. I've got a question regarding the current feeding the EL34s. Seems like the T2 uses 10mA over 1,000V vs the BH at 25mA over 800V. How does the power effect the sound. I know everyone's been talking about the higher voltages impacting the slew rates, but what is the optimal power for driving O2s?