June 30, 201411 yr It's very stable once it's warmed up. Tubes vary though so adjusting the series resistor to the pot might be needed but that's true of the KGSSHV as well.
July 1, 201411 yr That little guy looks awesome, Birgir. Using normal standoffs and standard tubes, would you be using a 3u case?
July 1, 201411 yr You only need about 90-100mm in height so 3U is plenty. This one was built into a 3U chassis: I'll take better pics when I prepare to list it for sale (only need one amp here) but there is a lot of room in there. That chassis is 300mm deep which will work just fine with the KGST power supply. It's just slight bigger than the one I used in that amp so we could use larger capacitors (in diameter that is) and put proper heatsinks on the 10M90 current sources. Nice! Did you build this one at 400v? Yup, this one is running at 400V and sounds just lovely with RCA tubes. A slightly different take from the KGSSHV and it's fun to compare it against the mini KGSSHV given the similarities in PSU, voltage and power. The servo settles at around 2V for one channel which is good as I could just manually adjust it to 6V. The other one hovers around 0V. Not bad at all...
July 2, 201411 yr What do you think about cutting holes in the top plate for the 10m90s heatsinks as well as the tubes and populating everything else on the board on the bottom side, then putting the PS on the bottom but making sure the pass FET sinks aren't directly underneath the amp boards?
July 2, 201411 yr That would work but you have to leave enough of the 10M90 hidden as the tab is live. Personally I'd just place the 10M90 on an external sink of some sort.
July 2, 201411 yr Author I have seen plastic covers for to220 transistors before. Where I have no clue
July 2, 201411 yr http://www.digikey.com.au/product-detail/en/THINC22-TO220-16-11.4-5.8-0.3/1168-1953-ND/3878142 http://www.digikey.com.au/product-detail/en/THINC23-TO220-21.5-11.4-5.8-0.45/1168-1956-ND/3878145 http://www.newark.com/richco/iec-to-220-18/cover-iec-to-220-pk25/dp/34M6452 http://www.westside-supplies.com/pdf/cats/Terms&Bush.pdf
July 3, 201411 yr Hi Birgir..... I am too new to Head-Case and I can't pm you or reply to your ad in the Trader Section. I'm interested in building the KGST and saw a few nice pieces in your ad that I would like to purchase. Please pm me if this is possible. Thx
July 6, 201411 yr Author coming soon to a file server near you http://gilmore.chem.northwestern.edu/kgdt.jpg 4.15 x 4.17 inch think of it as a cheap swiss army knife of electrostatic amplifiers works with any standard dual triode suitable for voltage 1 per channel Russian 6n1P, 6cg7,6fq7,ecc99,12bh7.... NOT designed by morons with just a digital voltmeter NOT open loop Not high distortion rationally priced (you get where I'm going here) Edited July 6, 201411 yr by kevin gilmore
July 6, 201411 yr The real problem are the tubes as not many can handle more than 300V. Push them hard and it all falls apart... The only dual I can think of that is rated for 500V is the 6CM7 but it's a dissimilar triode so not suitable for something like this. That said some of the computer tubes and TV tubes were meant to handle 600V peaks (or even higher) so they might fair well. The amp features switchable heaters on the board for 6.3V so either pin4 and 5 or pin4+5 and 9 for the 12V units. It also has switchable CCS so the current can be lowered with a jumper for tubes that can handle less power. Right now the list of tubes this one can use is : ECC99, 12BH7, 6N6pi, 6CG7/6FQ7, E182CC, 6840, 6350 and 5687. Should be more out there... Edited July 6, 201411 yr by spritzer
July 7, 201411 yr The plus side is also how cheap it is to build and everything is in current production. No SMD parts either as the voltage is low enough to use KSA1156's and Antek transformers will work perfectly. A pair of ECC99's is about 35$, 12BH7's less than that and 6N6pi's way less than that. I also bought some parts to try a KGST with current made tubes.
July 10, 201411 yr Looking for the specs for the power transformer needed for the KGST. Looks like the PS PCB inputs 2x 280-325VAC and 36VAC CT (each at what current load?). Plus will need 6.3VAC [email protected] for the 6S4A heaters on the amp boards. Any other requirements? Thx.
July 10, 201411 yr Are you guys recommending a similar soft-start for this amplifier, like the megatron?
July 10, 201411 yr If you want to run it at +/-400V then you need 325-335VAC rails. 280VAC for +/-350V. For current 110mA is sufficient but I'd shoot for 140-150mA to be on the safe side. 30-36VCT is about 500mA. Heater windings should not be CT as they have -400VDC floating on them. You have to have two heaters or you will have massive problems so one for each board. 1.5A is more than enough to account for the variables in the tubes. No soft start for me as I simply don't think it is needed. The tube won't arc at these low voltages.
July 10, 201411 yr Thanks Birgir, for the specs and your tip on no CT for the heaters. Never seen -400VDC in my previous tube amps built for driving speakers and headphones.
July 10, 201411 yr The cathode sits at -400V which is well above the heater to cathode limit. Most "normal tube amps " (as in designs as old as the hills) have grounded cathodes so this is less of an issue.
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