spritzer Posted September 6, 2014 Report Posted September 6, 2014 We want everybody stay at 350V. 400V is most certainly a "do this at your own risk" affair.
chiguy Posted September 6, 2014 Report Posted September 6, 2014 I'm going to be using Par-Metal 12x12x4 cases with 7/16 inch standoffs.
Sr Marqués Posted September 8, 2014 Report Posted September 8, 2014 Thanks, Birgir. Maybe 350 V is just enough for a beginner. Hi Torpedo, Here we are two beginners, I'll try to build this one, especially after saying that it eats the 717 for breakfast...
spritzer Posted September 8, 2014 Report Posted September 8, 2014 It has more power and is more neutral so yeah, trounces it easily.
chiguy Posted September 8, 2014 Report Posted September 8, 2014 I'm still waiting for a transformer but as of now, I've gotten the PCBs completed. What I'm wondering now is what are the proper power-on and setup procedures? This is what I'm thinking. Some dumbness/ignorance here so feel free to correct me: PSU Connect transformer to 115/230v AC mains via input recepticle with fuses Connect 280VAC and 30VCT to the PSU Do I need a dummy load on the PSU before powering on? What can I use? Power on, measure DC outputs, measure Bias voltage using the Bias test point. Adjust trimpot as needed. What does the trimpot adjust? All the GND connections go to chassis ground? Amp Leave the servo opamp out. Connect the DC power inputs. Connect the AC Heaters. Insert tubes. All the GND connections go to chassis ground? Do I need to connect the outputs? Do I need to connect the inputs? Adjust the balance. Adjust the offset. Power off and insert the opamp. Check heatsink temperatures. Am I missing anything? Thanks!
spritzer Posted September 8, 2014 Report Posted September 8, 2014 No load for the PSU needed. It's regulated so you will see pretty much the same numbers with and without the amplifier boards present. The trimpot is a voltage divider and thus adjusts the bias supplies voltage doubler potential. All the GND connections are connected together on the ground plane on the PSU PCB. These aren't connected to chassis by default so you need to run a wire to the chassis, either direct or through a ground loop breaker. I for one always go direct. For the amp boards, each one has one wire to the PSU ground, don't connect them to the chassis as that will generate ground loops. No need to conect input or outputs when testing Also remember to power off before inserting the servo opamp. Better yet would be tom use the jumper in the position marked "servo"
Laowei Posted September 8, 2014 Report Posted September 8, 2014 (edited) For HV tubes amps, I use a variac to slowly bring up the power for the first time and monitor the voltages. Keeps things from going BANG!. Edited September 8, 2014 by Laowei
spritzer Posted September 8, 2014 Report Posted September 8, 2014 Takes all the fun out of it though...
spritzer Posted September 11, 2014 Report Posted September 11, 2014 This one was just fired up. To say it was a tight squeeze into that box would be putting it mildly... Utterly oversized transformer courtesy of my Chinese supplier. 1
purk Posted September 11, 2014 Report Posted September 11, 2014 How much bigger is this amp is to your current KGSSHV mini offering Birgir? How about the sound?
chiguy Posted September 12, 2014 Report Posted September 12, 2014 Aside from the transformer being larger than specified, are there any issues (or benefits) with using a larger transformer?
nopants Posted September 12, 2014 Report Posted September 12, 2014 should run cooler, but in that tiny enclosure maybe it's a wash?
Laowei Posted September 12, 2014 Report Posted September 12, 2014 This one was just fired up. To say it was a tight squeeze into that box would be putting it mildly... Nice work! On your PS, are you simply bolting the two FQPF 9N90C mosfet voltage regs to the chassis as a heat sink?
spritzer Posted September 12, 2014 Report Posted September 12, 2014 How much bigger is this amp is to your current KGSSHV mini offering Birgir? How about the sound? Here they are together. KGSSHV mini quite a bit smaller. As for the sound they are very similar. The ST is a bit warmer and more fluid but that's it. Aside from the transformer being larger than specified, are there any issues (or benefits) with using a larger transformer? Just look at the Antek units as they are all oversized so the pro's are less heat, less noise from the transformer but the negative is more inrush current and more overhead for the PSU to deal with as heat. Nice work! On your PS, are you simply bolting the two FQPF 9N90C mosfet voltage regs to the chassis as a heat sink? Yup, it uses the chassis as a heatsink but this is a special version of the PSU.
chiguy Posted September 12, 2014 Report Posted September 12, 2014 Hmm okay. I'm going to be using larger transformers (110mm diameter x 75mm height) so I guess I'll see how that goes in a few weeks when I receive them.
Laowei Posted September 12, 2014 Report Posted September 12, 2014 I called Antek last July inquiring about their out of stock AS-1T275 and was told it would be in the "next shipment" in the first part of September. Called today, and it is not expected to be in stock until their "next shipment "in November. So I went with a custom SumR. Going to stuff everything in the same case as Birgir. Its my first electrostatic amp, and you know what they say about imitation.
chiguy Posted September 12, 2014 Report Posted September 12, 2014 Which case is that by the way? Also, what are the recommended fuses to use for this amp?
Laowei Posted September 12, 2014 Report Posted September 12, 2014 (edited) There are several of these same Chinese made cases on Ebay. This was the least expensive when including shipping in US that I found. http://www.ebay.com/itm/251509708498?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT One word of caution, by the inside dimensions on the ad and seeing Birgir's build, its going to be a TIGHT fit. Edited September 12, 2014 by Laowei
spritzer Posted September 12, 2014 Report Posted September 12, 2014 (edited) Looks to be the same case but I just pulled them from my pile of boxes. A note though, the KGST boards from the group buy will not fit in this box. The ones I used were specially made to fit it and they just barely do so. Also it runs hot... too hot. Chassis is at 43°C above ambient so I'll have to fabricate new top panels for these amps. The fuse rating depends on the transformer used. The amp draws about 60W. Edited September 12, 2014 by spritzer
Laowei Posted September 12, 2014 Report Posted September 12, 2014 Looks like I get to start my own pile of boxes.
chiguy Posted September 16, 2014 Report Posted September 16, 2014 I'm going to be using a 135VA transformer with 117VAC. So 135/117 is 1.15A. I'm guessing a 1.5A (or 2A) slow blow fuse will be suitable?
spritzer Posted September 16, 2014 Report Posted September 16, 2014 It really depends on the inrush current of the transformer but a 3AT would be my pick for US use.
insanity Posted September 18, 2014 Report Posted September 18, 2014 My KGST is up and running. Got the transformer yesterday from toroidy. As expected it is dead silent. Everything seems to work fine, no explosions. Balance and offset can be zeroed. Haven't had a chance to connect a source and headphones yet. I'll probably do this on the weekend. Uncased pictures will follow on the weekend.
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