mwl168

My bad, I meant to say the rectified voltage from the 360vac would be around 490V, not 390V, after deducting the forward voltage drop of the diodes. So I was surprised I was getting less than 480V. The transformer is just a standard Antek 200VA with 350v secondaries ( http://www.antekinc.com/as-2t350-200va-350v-transformer/).

Thanks Birgir. The voltage readings are all from a Fluke 112, nothing fancy but I would hope it can handle these voltages. The foward voltage drop on the STTH512 diodes are rated 1.25V. The transfomer secondaries are rated 350v/290ma. Based on materials I read, with 360v at the input, I was expecting to see the rectified voltage after the smoothing caps to be around 390V 490V. I am not concerned about the voltage just hoping to learn a lesson in practice.

Many thanks Kerry. I'll follow your recommendation. I forgot to mention the measured transformer secondaries were slightly over 360v with load. I am surprised by the magnitude of the rectifier diodes voltage drop. It seems to be much higher relatively than low voltage applications.

I have a couple of questions about the KGSSHV PSU (kgsshvps8g schematic, kgsshvpsminifinalstn9360 board): I set up the PSU currently to output +/- 400V and configured the pre-reg zener string for 450V (3 150V zeners). The rectified voltage from the transformer secondaries are -479V and +477V measured with load of the amp. It appears I was extreme unlucky picking the zeners - the actual zener string voltage I measured after the amp is fully warmed up is -476.8V and +448.5V. The -476.8V is 6% off, just outside the 5% spec'ed zener part tolerance. The actual output voltage of the PSU is -405V and +408V with load of the amp and has been very stable since the amp was built probably a month ago. My two questions: 1. Should I be concerned about the -476.8V zener string voltage which is almost right at the rectified voltage? Should I start swapping zeners between the two rails to bring it down? 2. Given the zener string voltage, how much higher can I safely raise the regulated output voltage? Is it OK to go up to 420V or 430V? If I understand Kerry's post correctly, it seems to indicate I need to give at least 20V headroom for the regulator to work properly. Thanks in advance for your help!

My build drives my LCD2 (50 ohm impedance) as well as I have heard them. I configured mine to run on lower voltage rails (16V ) so I can raise the output current. Don't have other ortho cans so cannot comment on how it may work on vintage orthos.

How did you get the edge of the holes so clean-cut? All the holes I drill on aluminum plate leave rough edges on at least one side.

I still don't have a device to accurately measure the heatsink temprature yet. To speak in general terms, in open air, the heatsinks never get more than slightly warm to the touch even after hours of driving my 007. The heatsinks do get appreciably hotter ( I can still put my hands on them with no worry of getting burned ) when I put the cover on so the heatsinks are entirely enclosed inside the chassis. The offset does rise quite a bit with the higher heatsink temprature. Your heatsinks are much larger than mine and exposed to open air. I would be very surprised if they get more than warm to the touch. This is assuming you are running the stock 120R in R5 and R6. No sure if this answers your question.

Great build Kingofsnake! Congrats!

That's too much screwing around guys!

I have the off-board version of the KGSSHV amp boards. To share my experience of the offset adjustment (measured between O+ and GND and without the servo); the offset can drift as much as 30V from cold start to when the amp is fully warm up. After I adjust the balance and offset to within a few hundred mV when the amp is fully warm up. If I then power down the amp and restart it a few hours later, the initial offset is often in the - 20 something V and gradually decrease to a few hundred mV and then drift back and forth a bit afterwards. The balance usually is within a few volt difference from cold start to warm up - much less drift compares to the offset. Your offset figure does not look out of ordinary to me.

I am planning to put my KGSSHV PSU in a separate chassis from the amp boards as well and have been looking at Amphenol military grade connectors at Mouser like John suggested. Some of the ones I looked at are rated at 600V and should be safe for this application. I'll find the Mouser part number and post it here tomorrow. I also have a question too - what's the reasonable length for the connecting cord? I like it to be long enough to have the flexibility with the PSU location but not too long to compromise the performance of the amp. Edit: Here is a female, panel mount 6-pin connector from Amphenol's ML-C-26482 series. This one is rated at 600V, 7.5A. Mouser part number: 654-PT02E-10-6S.

Has anyone purchased hard-to-find transistors from pacificsemi in Vancouver Canada before? Are they reliable? Looking to buy a few pairs of 2SK216/2SJ79. Found them at BDent and pacificsemi. BDent price is 50% higher than that of pacificsemi. Thanks!

That's truely amazing craftsmanship. Congrats Kerry!

Hi: I just placed an order to have 10 sets of KGST boards made. A few of them are already spoken for but I should have 5 sets available to those interested. Here are some details: 1. The amp board is KGST6S4CASCODE (120mm x 135mm), the PSU is KGBHULTRAMINPSV4 (105mm x 134mm). 2. The boards are all 2mm thickness, 2oz copper, green silkscreen with white lettering. I wanted the thicker board that can better sustain the mounting and dismounting of the tubes. 3. I am using a PCB fab house in Taiwan which was recommended to me but I have no prior experience with them. 4. JimL has traced the cascode CCS part of the KGST6S4CASCODE board (see KGST thread), I traced the rest of the board by comparing it to the KGSTMINV03 board. However, to my knowledge, no one has built the KGST6S4CASCODE board yet so it should be considered un-proven. 5. The cost for each board set ( 2 amp PCB and 1 PSU PCB) is $50 USD plus applicable PayPal fee and shipping cost from me to you. 6. I may potentially have one set with 1.6mm thick, 2oz copper KGSSHVPSMINIFINALSTN9360 PSU board available but cannot promise. Please respond to this thread if you are interested. If there are more interests than can be accommodated, inclusion will be based on a first-come-first-serve basis (FCFS). I will PM those respond their interest with my PayPal account and further logistic information. please let me know if you have questions. Thanks!

Sorry, I was being sarcastic – jokingly saying we should start a GB for the water cool chassis for T2.

The ad is for a "KG T2 chassis kit" that includes the chassis, internal accessories and the water cooling mechanism (including the water pump and it's own power supply). The ad says the water cooling mechanism is "highly reliable". I think the $15000 price is in Chinese Yuan which is roughly $2500 USD based on 6.22 exchange rate. The kit is made to order. It takes a mighty brave soul to try this thing out. Edit: It says discount is offered for large quantity order. Should we start a GB?

Thanks John. I do have the 2K resistor (R26) in series with the offset trim pot. I have considered using your trick (read your earlier post) and parallel another resistor on top but the space is rather tight where the 2K resistor is on this board. I may still do it since I was also thinking about using the same trick on R5/R6 to bring them down to around 100R. The good news is that there is plenty of space around R5 and R6. If I do so, I'll for sure need to lower R26 one way or another since I expect increasing the output current will raise the DC offset.

Thanks nopants. I had the amp running for more than 4 hours with the cover on. The heatsinks don't seem to get hotter after the first hour. The problem I have is, at the higher operating temperature, I run out of range on the offset adjustment. Activating the servo may get the offset close to 0 but I have not tried that yet. I am also not excited about the option of taking apart the amp board and heatsink assembly to replace the resistor in series with the offset trim pot to get wider adjustment range. Of course I may not have much choice come summer time with higher ambient temperature. My plan is still to re-case the amp in the coming winter.

The video is for KGBH which I have no knowledge of. There are two trim pots on each channel of the kgsshv; the 2K one is for balance and the 1k for offset. I am assuming this is the same with the version you have (I have the V0.91 off board heat sink version). Hope this helps!

I followed John's wiring diagram and read the excellent Rane papers as well ( Thanks John!). I connected the PSU ground (I use the one from the +/- 15V) to the star ground. No connection to the star ground from the amp boards. My amp is silent without any hum or buzz when no input signal is present. When I first wired my amp into the chassis I forgot to make the ground connection and I had problem with high offset voltage. Once I connected the PSU GND to the star ground I was able to adjust the offset to 0V.

This may be stating something obvious. The readings between L+/L- and R+/R- are balance. The offset is between either of the output phases to ground. Adjust the balance and get it close to 0 first then adjust the offset. The two adjustments are controlled by two separate trim pots on each channel. You will likely need to go back and forth between the two adjustments to get both to 0. Also these adjustments need to be done without the servo activated.

Yes, the cover has cutouts for air circulation on both the top and the sides. I am surprised at how much the heatsinks temperature rises with the cover on.

An update on the heatsinks temperature. I put the cover on my temporary chassis today and after two hours the heatsinks went from slightly warm to the touch to hot to the touch. I can rest my hands on the heatsinks without getting burned but they definitely feel uncomfortably hot after a few seconds. Also, the offset shot up to about 30V. The room temperature was about 65F. Both the 2SC4686a and 10m90s are rated to 150F and I've read comments that if you can put your hand on the heatsinks for more than 5 seconds then it's probably fine. So I am a bit concerned but not worried ) My thought is that the heatsinks I use are fine if they will be exposed to open air. I would probably use bigger ones if just for the peace of mind if they will be enclosed inside the case. I would love to hear the thoughts and advice of those that are more knowledgeable.

Yes, that's the one I use. I have not experience any hum nor buzzing and it runs cool. The downside is the size - this thing is HUGE )

The Tsar has already spoken but since I just built a 400V KGSSHV using a similar PS (kgsshvpsminifinalstn9360) I can also share my experience. You can also referred to my earlier post #4321 which has the exact value of resistors I used based on availability at Mouser at the time. The formula to calculate the B+ is ((R29 + R5)/R6 + 1) x 10V (V out of the LT1021 voltage reference) and similar for the B- side of course. I also read that you should configure the pre-regulate Zener string to 50V above your desired voltage, in this case, 450V. In my case, I have been getting a very steady +408V/-406V output from my PSU. Hope this helps.