if you live in the SF area, you'll see this on CL. I'd say pickup only, but you're welcome to arrange shipping :-)This is the culmination of over a half year of steady work. Dual Mono Block, Push Pull Parallel 6550EH stereo amplifier. I put so much time into this it is ridiculous, and let's be frank, so is this amp. At a little over 80 Watts per channel (a real number, I measured), this thing is impressive. She weighs in right around 150lbs. There wasn't much I spared making this thing to say the least. Input is a constant current sunk 5687 LTP. Then into a forced differential 5687, also CCS. And for the finale, all 8 of the output tubes, the 6550EH, are also CCS. Oh yeah, and no LM317 crap...All of the CCS are cascoded pairs of IXTP08n50D2, and IXTP08n100D2. Controls up top of the chassis to set the operating points of your input, your driver, and your outputs to wherever you like. Right now I'm running them at 8ma, 15ma, and 62ma, respectively. The meters on the front are switchable to show one side of output transformer, the other side, the driver, or the input. And of course, there's one meter for each channel. The two power switches are one for heaters, and one for HT so no cold turn on. The meters on the bottom show the total current for that channel, I've been running it at 300ma+ per channel, for 12 hour days, and she's just chugging away. I think the CCS on the output tubes, forcing balance in the push pull arrangement is pretty cool....but what about DC balance with such a big amp? Well there's also pots sunk into the chassis for that. See the speaker terminals up top? Hook your multimeter up to them, dial in the pot, and have an amp that is within 1/10 of 1ma DC balance! Pretty slick, IMHO. So what are those huge transformers we're balancing? Those are custom order Electra-Print. 3.3K P-P, 100W, -1db (that's right not -3db) from 21Hz-49Khz!. Good for 250ma per side, so they're also loafing along with the 150ma per side they might see with the 6550's....but, again this is where the CCS is so neat. You want to try a completely different operating point, bias them way hot or cool, simple turn the dial, and watch your cathode voltage on the meter, and you're there. Reset the DC balance and your amp is as tight as it gets as far as biasing and matched tubes goes. Oh, and I had jack wire it with 4 and 8 ohm taps. Oh, one more thing, it's running Ultralinear. The power supplies are completely separate for both channels. The layout is C-L-C-R-C, and the values are 66µf-10H-120µf-100Ω-220µf. Then, there's an extra 400Ω and 60µf for the drivers, and a further 660Ω and 60µf for the input. Stable voltage, overkill I know. But what the heck, I was having fun with these Poly caps and Oil caps. That's right, not a single electrolytic in the whole thing. No replacing capacitors down the road. Also, as you can see in the pics, all grounds return to center taps via 12ga. ground busses. The construction is pretty die hard. All the lifetime poly and oil caps. The box is 3/4" Maple. The trim is Redwood/Maple. The lid is 1/8" aluminum (aircraft). All the wiring is teflon/silver wire. The heater supplies are separate for every pair of output tubes, and for both channels in the front end so no crosstalk coupling. Coupling caps are 1000V Gudeman hermetically sealed .22 NOS, not pulls from some other piece. Heatsinks for the PP CCS are on nylon standoffs, with the Mosfet touching the heatsink and also the chassis, so effectively the Mosfet see's a HUGE heatsink, as they are right underneath the OPTs. The driver and input CCS both have overrated heatsinks as well. Something like this is an investment for sure. I have over 2000$ just in parts, and would be happy to break it all down for you. This is a labor of love, and I've been putting off posting it for a while. I'm posting this in a few different cities and some of them I don't even expect a response, but I like to put my work out there. It's a special thing to be able to drive 86db/1W/1M speakers louder than I can handle, with a tube amp. This thing opens up some doors for speaker lovers who have had to traditionally use SS. It's going to be a pickup thing for sure, but I'd discuss meeting the right person somewhere. Really though, you should come here and hear it. You will fall in love. I know I have, I hate to sell it. But there's always the next project for someone like me, hi hi. I've included a bunch of pics, but there's so much more to say and show. If you're interested let me know. I'm always open to trades, and I also have some other less expensive amps I've made. Though honestly, they are not anything you can't find elsewhere. This is. If you know tube amps, you know something like this does not come up for sale often. I hope to hear from some people out there, if for nothing else than engaging conversation. Thanks all, have a great day, LC
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