I find that getting the parts is the hardest and most frustrating part of a build. Soldering is kind of meditative, except the noise of the fume sucker gets on my nerves. Wish I could listen to music. Chassis work is the most annoying though, unless buying professionally done I go for utility rather than cosmetics, because I don't have the patience for nice cosmetics. Or rather, I don't have the tools. I do have access to a machine shop at work but feel pressured. It would be easier if I had it all at home. Anyhow, a final maddening push at the end (always more bits to do then you originally though), and you're all done.
KGST should be pretty easy for most people (just finished one). KGSSHV (what I'm doing now) is a touch harder. Mighty Megatron is next, summertime probably (have all the parts except the Mouser bits). Then, I summit T2. Anyhow, it really doesn't take all that much time. Mostly it's internet time figuring stuff out and buying parts, which is easy. If you've got everything ready than assembling is fairly fast.
You put your finger on the exact difficulty. The answer is no, it's DIY and evolving designs, BOM's you find on the net get out of date, parts go obsolete, etc. That's why I said getting the parts (and also figuring out some assembly details) the hardest part. You have to make a list from your circuit board which I don't have a talent for.
Best procedure is to secure a board, then take a few weeks going over it. Make a printout of the mask and check off the parts list, then assemble a BOM in Mouser. Triple check it. By then you should have a good idea of the assembly (e.g. 450VDC vs 500VDC for kgsshv build), get the parts and go.
Also, when buying resistors and other cheap parts, always round up.
Here's the original BOM for the amp boards:
Some of those parts might be out of stock now but finding replacements usually isn't too hard.
Beautiful build Enrique. It's kinda my fault Frank hasn't heard it yet...I have my boards populated and casework ready, I just haven't wanted to even look at it since I blew up the power supply on initial power up. Troubleshooting it is pretty daunting.
Thanks Milos. Sorry I missed you and Frank at the meet. Chicago was awfully cold that weekend!
I am having some minor issues with intermittent humming in the right channel; other than that it sounds great.
I agree with you though, troubleshooting can be a pain, bit it is worth it.
Here's a couple of ideas that might aid in troubleshooting. Bear in mind that I have never built or even seen a Megatron.
Milos - Despite the obvious damage to your supply board, you probably have the easier task. Almost certainly you have a wiring error, solder bridge, or reversed component.
Do you have an actual burned spot on the board? Which supply (pos. HV rail, neg. HV rail, low voltage ) actually blew up? If nothing at all works, then you need to look at the early part of the circuitry where there are common elements to all supplies. If only one supply blew up, I would disconnect it and retest the other supplies for normal operation. Once you've got it isolated to a particular supply, inspect each and every component for proper value, polarity, position, and physical integrity. You will probably find something like a reversed electrolytic cap, a wrong valued resistor ( I still sometimes misread color codes), or a backwards TO-220 component. If the board is damaged (broken trace), you will have to solder a wire bridge, or if the damage is too severe, then junk it and start over. Besides a minor repair of the board, I would not reuse any of the components in the blown supply. If you are able to repair the board, check and recheck the value and polarity of the new components as you install them. Keep in mind that the HV rails are mirrored and not identical. In each supply,measure the resistance to ground at each junction in the current path all the way to the output. If you have a zero or near zero at any point, you have a problem. If in the end, if you can't find anything, build another board. When building any circuit board based project, unless you are very familiar with the circuit, one should always have extra boards.
Enrique - You have the tougher task because it is intermittent. Next time the amp starts humming, try tapping the top of the case with a small dowel or unsharpened pencil in the area of the suspect 12AU7 ( are you sure the hum originates there and not earlier or later in the circuit?). If you can make the hum change by tapping in a particular area, then you probably have an intermittent connection at some nearby point. Reflow all nearby solder connections. Redo all your screwed terminal block connections. If this doesn't do it, try running the amp with an oscilloscope connected at different points in the signal path. If nothing works, rebuild this part of the circuit with all new components. I've had a problem similar to yours that was caused by a nine pin tube socket that wasn't perfectly soldered to the underlying board. It was the last thing I was looking for and took me way too long to find it. The socket and board were brand new. Everything looked and measured fine. For lack of anything else to do, I finally replaced the socket. Problem solved.
Hopefully someone who knows more about this particular amp than I will chime in. Or at the very least add some more general troubleshooting tips. If anything I have said here is incorrect or inapplicable, then please correct it.
I already took part the amplifier. Piece of cake. Putting together may not be
Troubleshooting and tinkering is half the fun
As far as the sound, it has "more meat" in the lower end than the KGSSHV with detail as good or better.
I do like it a lot and is well worth the effort.
The only difference between the off board and on board amplifiers assuming the exact same parts
is that the off board version with an appropriate heatsink is able to have the class A power turned
up more. The effect is subtle, and really only noticeable at the higher end of the frequency spectrum.
I have sr-009 and Stax SRM-007t standard. I know there are better match for the 009 but before I head down that route I want to give my 007t another chance. What are the mods to upgrade the unit? different tubes?