livewire Posted June 19, 2012 Report Posted June 19, 2012 (edited) >>MEGATRON<< The rollers are gonna have a field day. Twelve tubes, count em. Yay Team Overkill!! Edited June 19, 2012 by livewire
decoherent Posted June 19, 2012 Report Posted June 19, 2012 Kevin, what happened of the original design to resort to the usual EL34? I personally prefer real triodes to pentodes, even when triode strapped, and parallel 5687 as power stage did sound an interesting idea (also one of my fav triodes). What's the reason? Filament supply? Not enough gain? Simply more parts? Thanks.
kevin gilmore Posted June 19, 2012 Author Report Posted June 19, 2012 There must be 20+ original designs. I'm going to give away all the board files, and nothing prevents people from building whatever they want. But a compact monster amp can't be a bad thing. The thing with the 5687's is that they behave very badly if you push them over +/-300. And given the Rp of the tube, the most you can get is 1150 vppss. Since there are no 1kv triodes unless you use really expensive dht's you have to use el34's strapped as triodes.
kevin gilmore Posted June 19, 2012 Author Report Posted June 19, 2012 (edited) universal power supply with option for C- supply and time delay for tube high voltage http://gilmore.chem....versalpower.jpg updated amplifier board http://gilmore.chem.northwestern.edu/megatron.jpg Edited June 19, 2012 by kevin gilmore
Inu Posted June 20, 2012 Report Posted June 20, 2012 Minor issues.. Missing (or deleted?) the protective diode between the TL783 In and Out. Making "AC2" and "-" for the bridge rectifies (KBU4x) were reversed (patterns are OK).
kevin gilmore Posted June 21, 2012 Author Report Posted June 21, 2012 (edited) The pattern for the bridge rectifier, i'm aware of, but since the printing never shows up... but i will fix it anyway. How i missed the diode on the tl783 i'm not sure, i know where it cut and pasted it from, and the original has the diode ?? Thanks Inu. Edited June 21, 2012 by kevin gilmore
Inu Posted June 21, 2012 Report Posted June 21, 2012 (edited) Oops, Making > Marking. How about adding protection resistors (5.1K 1W) to the outputs? Edited June 21, 2012 by Inu
Inu Posted June 21, 2012 Report Posted June 21, 2012 (edited) If possible, For the 0.22uF/1000V Add extra mounting hole for the PCM 22.5mm capacitors (EPCOS) For the 0.1uF/450V(400V) Add extra mounting hole for the PCM 15mm capacitors (EPCOS and MKP10) Edited June 21, 2012 by Inu
kevin gilmore Posted June 21, 2012 Author Report Posted June 21, 2012 (edited) updated files http://gilmore.chem....du/megatron.jpg http://gilmore.chem....versalpower.jpg someone please check that i did not flip the feedback, or other stupids Edited June 22, 2012 by kevin gilmore
jezz Posted June 22, 2012 Report Posted June 22, 2012 On the power supply, I'm a little nervous about how close the 7912 output trace to the terminal block is to the heatsink mounting hole. Also, did you intend to ground the FET heatsinks? On the amp, all of the ground solder pads aren't split up to slow down the heat dissipation, so they'll suck to solder to on that size of a board.
kevin gilmore Posted June 22, 2012 Author Report Posted June 22, 2012 (edited) Moved the 7912 a bit. All of the heatsinks are grounded. It may not show up well. I made the thermal's thicker so that they can be seen now. I've never had any trouble with a regular soldering iron soldering solid ground pads. It makes a significant difference in the performance of the amplifier, those little crosses add a fair amount of resistance and increase noise. So i like to keep everything in the signal path with the lowest resistance to ground. Edited June 22, 2012 by kevin gilmore
spritzer Posted June 22, 2012 Report Posted June 22, 2012 Indeed solid thermals shouldn't be a problem for a good soldering iron. A good Weller or Oki isn't that expensive and makes soldering so much easier.
jezz Posted June 22, 2012 Report Posted June 22, 2012 Thanks for the info. I've got a 100W XYtronic which I've never had problems with. I was more wondering about how newbie-friendly this was supposed to be, though it makes sense that the Stax Mafia would put a good iron in every newbie's hands.
spritzer Posted June 22, 2012 Report Posted June 22, 2012 I tell every noob to just buy an OKI PS-900 and skip over the cheap stuff. I'm all for using cheap stuff where you can get away with it but cheap soldering irons are just that, cheap. Only exception would be the military surplus stuff Kevin brought to CanJam.
Victor Chew Posted June 23, 2012 Report Posted June 23, 2012 (edited) Am I correct to guess that the costs estimate for this build excluding chasis, volume pot, input jacks and tubes should be no more than US500 to US600? I believe the PSU should costs more? Costs of tubes is where the numbers will fluctuate greatly correct? Any default tube type or manufacturer recommended? Edited June 23, 2012 by Victor Chew
Inu Posted June 23, 2012 Report Posted June 23, 2012 Kevin, Not flipped NFB line. Each 6CA7 sinks or sources about 27mA (11W) is correct? 450V Line (included 300V line) = total 61mA/ch -450V Line = total 54mA/ch
kevin gilmore Posted June 23, 2012 Author Report Posted June 23, 2012 (edited) 27 ma per tube is exactly correct. The teflon octal sockets on ebay are about $10 each the teflon 9 pin sockets seem to be about $12 each likely way cheaper overseas. Not sure how much the capacitors are. maybe about $600 in parts total including the power supply, not including the transformer or the tubes. Edited June 23, 2012 by kevin gilmore
eggil Posted June 28, 2012 Report Posted June 28, 2012 (edited) Are PCB's planned for the Megatron? Edited June 28, 2012 by eggil
kevin gilmore Posted June 28, 2012 Author Report Posted June 28, 2012 (edited) Biirgir is going to do the prototype run very soon Edited June 28, 2012 by kevin gilmore
Victor Chew Posted June 28, 2012 Report Posted June 28, 2012 I can feel the sense of excitement. Will the DACT or other attenuators be incorpotated as an option in the boards?
kevin gilmore Posted June 28, 2012 Author Report Posted June 28, 2012 not unless people let me make the board bigger.
spritzer Posted June 28, 2012 Report Posted June 28, 2012 Given that none of us can agree on attenuators I do think it is best to keep them offboard. I certainly wouldn't be caught dead with an RK27 in this amp... When I have a bit of time I'll order boards from me and KG so we can test the beast.
Inu Posted June 28, 2012 Report Posted June 28, 2012 How about remove RK27 then use space for add 2SA1968 0.5mA (150mW) CCS option for the 2nd stage?
Horio Posted June 28, 2012 Report Posted June 28, 2012 I still like the idea of being able to board mount the attenuator. I'd be perfectly fine if the board grew a bit to incorporate a DACT attenuator.
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