I received a pair of 2SK180s + TDV boards in the BAF 2022 raffle, so I’m hoping to put a little amp together really soon. I did a quick prototype on the bench and gave it a listen. Excited for what’s to come!
Nice! I'll be curious what resistance value you land on in front of the choke. Guessing maybe around 2R?
With a bench supply of 15V and drain current of 2A, I was seeing about -2.5 to 0-3.0V on the gate of the sample I had. Once I decide on the power supply design (First Watt PSU seems to be the suggestion) and final supply voltage, I will experimentally dial in the resistance.
Thanks! Its an eBay special from China. I really like it. About a 4U/400 and has plenty of dissipation. https://www.ebay.com/itm/223591731160
As of today I got the 2SK180s mounted and wired up to the CYOF boards. Power supply is based off First Watt schems. 24vac fed, nominal 30V out. Static tests using a bench supply to the gates showed about -4.5v for 2A Id @ 30vds. The Hammond 159ZC chokes I have measure about 0.9~1.0 ohm (not super accurate here) so I figured I could parallel two 2.7R (had on hand) and that should give me enough. SITs are pretty decently matched and gave about 1.85A with 1.35R plus the chokes and just shy of 30v on the drain. I need higher wattage resistors long term, so I will likely go a little higher so the bias isn’t as hot. I measured a case temp of about 50C on the SITs when I turned it off. I was able to hook speakers up and get a little listen too, and it sounded alright with no hum.
Anyone know what a reasonable case temp is for these? Datasheet gives max junction temp and nothing else. The chassis as envisioned will see these sinks attached to a large and thick aluminum plate, but I’m not well versed in designing for dissipation on devices like these.
Anyone know what a reasonable case temp is for these? Datasheet gives max junction temp and nothing else. The chassis as envisioned will see these sinks attached to a large and thick aluminum plate, but I’m not well versed in designing for dissipation on devices like these.
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The 2SK180 datasheet doesn't give the thermal resistance figures. I could work backward as far as the case-to-heatsink, but without the junction-to-case I would ultimately be guessing at true junction temp. Once I have the right resistors in, I will do some tests to monitor the thermals over time.