RiStaR

Wondering how everyone else is coming along with their Megatron build? I'm getting jittery waiting for the call that the rest of my items have arrived. This is my first tube project so was hoping for more info before I plonk everything in and power it all up

Gratz Insanity There are also some tweaks in the thread (suggested by Justin) for if you have some noise once you add the stepper/pot. If I remember right, and I've seen it in pictures by a number of the folks here, it involves 100ohm resistors just after the pot (do verify).

You may have to check with LilKnight on the boards/GBs Most of us got the amp boards with the Krell psu (some with the old design and some with the new). You can use most ps boards really... Just need to get them to the +-15v that the square wave needs... The simple krell makes it easy with just Zener diode changes.

It's probably my resistors and capacitors... Tried to go local on this low voltage stuff. All the boards go smoothly except for the one that goes from 80 to 130+ smoothly then just jumps to 200 with a touch... Anything less and it jumps around. I'll swap the 50k to 75k to eliminate the pot being a possible factor I guess. At this stage it's done and has kept me occupied while waiting on transformers for the Megatron. Thanks for the quick support! I'm happy with this

Have changed the resistors... The 50k resistors help to adjust bias very finely but I encountered some problems with two of the boards. I'm using 1% resistors but it seems the tolerance isn't good enough. One of the boards refused to go above 30mA with the 50k resistor... Swapping back to the 75k one worked perfect. Probably my 34.8k resistors giving me grief...(can't access the schematic at the moment so I hope I remembered it right) The other problem board jumps from 140ma to 200ma with a very fine touch... Not able to set anything in between and fluctuates a lot once i get there. Not sure if its the pot acting up or what not. I intend to swap the resistor to 75k as well to see how that works. With the 50k resistor on the two "good boards" bias start at 60-80ma with the pot at minimum on my boards. With the 75k it starts at 128ma The opamp stacking worked very well with the 100k resistor.... On the good boards they never go above 0.8mv and mostly stay around 0.1mv. Even on the "bad boards" it stays below 2mv. I intend to run at 150ma for now since I fked up and got the smaller heat sinks (should have used a smaller depth and I'd have gotten the taller ones appearing on mouser ><). The sinks are just warm to touch at this setting. Overall, this has been a simple fun build even with the minor problems on this revision Sounds good, too - I understand why singlepower was that popular in the day now.

Thanks Kevin. Will be picking up those resistors - have stacked the opamps per your schematic and pictures.

I don't have a dummy load for testing around. And sharing that the readings never changed/fluctuate plugging the transformer to the kgsshv ps board isn't useful the transformer was at room temperature for the 10-15 mins I left it running. FWIW, a couple of local niche hifi shops do use his services (which is pretty high cost for something very plain looking). I got his contact from one of those stores. Cetoole: way to go to make me calm my own fears

I had it custom made locally because toroidy was having issues shipping over... Thing is on the day I got back from ordering it toroidy came back and said ok. Would have worked out cheaper and much smaller too! To be honest 430mA didn't seem excessive when I thought of it... I read 27mA per EL34 and some smaller values for the other 4. I figured with our usual 1.5 to 2 times for margin it was pretty close. Add in all the transformer issues people were having when having transformers so close to the actual rating of the kgsshv in the past, I thought going a 'tad' over would be ok. That is until the EI transformer came in measuring 134 x 110 x 115... Must have missed this out when I lost my post last night. I got the ideas for the change in resistors from talking to Victor. (15R to 10R for PSU and 1.5k to 1k on the amp board).

Thanks making this easy! I did flip the FETs when I put them in because of the pinout. Will work on this today and tomorrow. My wife thought the sound was amazing through the realiser then I told her that was just with the radio as a source! Can't wait to get this working properly. Have a plan to get it stacked on the 8channel ess9018 DAC that I'm also waiting on parts for. EDIT: never,ind the schematic is updated now... Pulling the opa134s did bring the offset down

I know... But I thought you'd be the first to approve! I'll take a pic of the EI core when everything comes together. Took me a while to find a case that'll fit all the bits I need inside the power supply. Waiting is always the hardest part with this hobby. I'm gonna turn in for the night. Have a good day the rest of you!

I kind of went overkill on it... HV 420V 430mA x 2 17-0-17 1.2A 6.3vdc power supply 9v 30VA 6.3vac filaments Using 3 (2x 30VA; 1x50VA) For the PS board I'm using 2222A instead of 3904 and have changed the 15R to 10R so hopefully I won't have a problem with current. The PSU currently powers up fine without load. Waiting on the lv transformers to power up the amp board. Fingers crossed I get music on a flick of the switch Just checked my squarewave amp boards and I have some issues I can't get the DC voltage down... two of the boards are -2v and the other two are like 1.6-1.9v ... will have some time to debug over the weekend. Not quite sure where to look, yet

While waiting for my transformers for the megatron, I've completed the Squarewave with KG's help on the Krell power supply. Just tested it single-ended with the lone transformer that I had. It's definitely worth the build... Not too expensive and makes my HD650 sound big. Gonna go try to find another amp to compare it with, but I'm liking what I'm hearing

Very nice Kerry! Cee Tee that looks awesome as well! Sorry for the noob question, but is that the final finishing? What is it?

I've looked into this in the past and I think the PNP part is: http://www.sm0vpo.com/_pdf/2SA/2SA1968LS.pdf Only reason why I found those is that I chanced upon some 1968s that were marked 1968LS but they are non-isolated - they test fine in the transistor tester so I assume they are remarked 1967s? The ones that I got from Sato Denki don't have the LS label but they are isolated like you expect. At this point I'm testing the non-isolated ones in the Megatron that I'm building... just waiting on the transformers and my LT1021s to show up before I can power everything up.

Hi Insanity, I'm pretty sure I'm using these 3900pf capacitors in my 0.5 version. It's 630V and I haven't had an issue with them since I got it up running for more than half a year with daily listening http://sg.mouser.com/Search/ProductDetail.aspx?R=FK20C0G2J392Jvirtualkey52130000virtualkey810-FK20C0G2J392J (Please note: It's on an SG site)

Yep. And you need two windings at the minimum. Trying to go all overkill on this one since the tubes draw so much more power... toroidy is having difficulty with shipment to where I am

nopants you're using two of those Hammonds?

I got most of the info on that from the post below by Kevin. Is it the one you're talking about? @Kerry That really does look very compact! Really looking forward to seeing the completed project

Thumbs up!

Okay, here's a tip. The posts that say "great job" etc are good search terms for you to use. Here's why... these are often posts that follow a successful build with lots of tips and pictures. You know, the stuff that you actually want and have difficulty with (like wiring, putting in parts etc.) Make use of the search terms you "don't like" to do the things you want to do. When you find those posts you can quickly scroll back to find the ones that you're looking for without having to weed through all the posts that you're finding so troublesome. The vast majority of us aren't electronic engineers, too. You don't need to feel out of place. The folks here get agitated only when you ask questions - when it's clear you haven't tried to search. If you're looking for clarity over certain things with which you've researched you'll find help and answers really quickly from very helpful folks (I know I've benefited from that very quickly). I'm also going to bring to attention something that you've not picked up on also. The boards that you've just ordered (I'm assuming the onboard version) are based on a new revision (new layout; new replacement parts etc). The only folks who have really built this version are Lil Knight and Spritzer, I think. So please note that the vast majority of us don't know all the details, either. The majority of us have built it with the older (more expensive; hard to find) parts. If you're still not getting what I'm saying, it'll be good for you to focus on images for wiring, layout and things that have caused folks to blow their amps (which it seems to indicate you'll have problems with?). There really shouldn't be a need to worry about board issues like traces being reversed etc... the KGSSHV platform is relatively mature IMO. I'm going to wish you good luck and hope you can turn things around for you on the forum. Like I said, the folks here are really nice and helpful as long as you don't demand things from folks who don't owe it to you.

It takes a while and it can actually be beneficial for you to sift through so you will know some of the troubles encountered by others and pay extra attention there. It is high-voltage (can be dangerous). I do also think you're not registering things that you read properly. Pretty sure the "500VA and 450VA" you're quoting is actually the voltage of the power supply... even though overkill is fairly common here, a 500VA transformer is going to be way huge. Just to be clear, the amp runs as 500V (for IXYS) or 450V (for 1968s). Unfortunately, this stuff isn't sold as a kit... so there really aren't instructions but shared experiences. Give it a while, you'll find that the folks here are really nicer than it seems.

It'll probably help if you'd take a proper image of the board so folks can have a look at it. There have been a few in previous posts where things are missed (isolators and what not) that were problems. There have also been cases of folks plugging in excess parts when they shouldn't (e.g. 450v parts for a 500v PS and parts for IXYS instead of A1968s etc). In both instances a photo can help folks to diagnose for you

Thanks for clarification

Thanks for working on the BOM chiguy and palchiu... but if i'm not wrong the 5.1k resistors should be rated for 1W?