George, we use a lot of Toshiba 2SK3878 for welding inverters here. Rugged 900V 9A part, SOA 400 ma @300V, EOL but still widely available for ~ $1 here. Substitute is supposedly TK9J90E, but SOA is only 300ma @300V, should be < $3 from mouser/digikey.
ra7,
I am close to having four working channels - always something missing which slows the project down.
I am using 5k/10K in the Schade network.
I would assume this would consume less current than the standard 1k/10K version and the setting as specified in your instructions is what I should use?
My second power transformer is due today so I hope to have it working by this weekend.
Then to begin the power amplifier work which will be simplicity in comparison,
Thanks and take care,
I am close to having four working channels - always something missing which slows the project down.
I am using 5k/10K in the Schade network.
I would assume this would consume less current than the standard 1k/10K version and the setting as specified in your instructions is what I should use?
My second power transformer is due today so I hope to have it working by this weekend.
Then to begin the power amplifier work which will be simplicity in comparison,
Thanks and take care,
The ratio of the two resistors do control the overall voltage gain. The series combination of the two resistors determines the current "wasted" in the feedback network.
The very first Schade common grid amp used a large vacuum tube for the gain device with a plate voltage of up to 650 volts, so I used a 33K/300K set of resistors to reduce power dissipation. Here the grid capacitances are very low and have a very weak and lossy (low "Q") dependence on applied device voltages, so high valued resistors are acceptable.
Some of the mosfets used in the SCG builds have considerable gate capacitances which vary quite a bit with the applied audio signal. This can lead to variable phase shifts in the applied feedback with respect to the signal frequency which may cause a perceptible distortion effect that is hard to measure. The 10K/1K pair is probably a good choice as we can afford to waste a few milliamps if needed. 10K/5K is OK if a voltage gain of about two is enough. I needed a gain of 20 to drive a single stage vacuum tube to 20 watts, and something similar for the fat mosfet output stage.
My current high power stage runs on 300 volts and uses a 150K/10K pair, which is too high, but it's easier to stick resistors in parallel with them than to change them, so that is OK for now. They will see some changes as I "tune" the board, but all progress is on hold for now.
For some unexpected stroke of USPS bad luck they have lost my Mouser order with several thermal solutions and some mosfets, as well as the large check that I sent to a bank to rollover my 401K. The Mouser stuff I can live without, but the 401K rollover check issue can subject me to about $50K in taxes and collateral losses if not deposited quickly enough. The USPS guys are "looking for it."
George, i was in similar situation with 401k rollover, due to moving to different address. My suggestion is to request new check asap and deposit that one. If the first shows up, fine, destroy it. Still no one else can (presumably) deposit first one if lost.
It was the USPS not UPS. UPS rarely loses things they just break them. There were 6 mosfets for the gain position in my high power SCG breadboard on the order, Mouser had 10 and Digikey had 1. Now Mouser has 3 and Digikey has 0. I may or may not get 6.
I worked for Motorola for 41 years. Some Wall Street Wizards bought into the company heavy enough to get two of their henchmen on the board of directors, and eventually assert enough control to break up the company and part it out like a junk car. During that "optimization" period about 100,000 people worldwide lost their jobs and everything was outsourced including the pension fund and 401K management, probably to the lowest bidders. The 401K management went to one of those high fee financial companies that advertise on TV. We must have wound up on the lowest tier of service because it was nearly impossible to get a human on the phone or move my money out of their company via their web site. It took nearly two months for them to finally send me a check. They refused to send one to the new institution or even acknowledge their correspondence. I sent their check to the new institution directly by certified mail with tracking on January 7. The check was within 3 miles of the new institution on January 9, and was dispatched to the "next facility" on the morning of January 10. It was never scanned again, and the tracking still says, "moving through network, in transit, arriving late."
I spent the day yesterday Googling up the phone numbers of every USPS facility in the Salt Lake City area and calling them. In my random calling I stumbled upon a USPS "consumer affairs" office and a person who tried his best to help. He said he would call back in an hour and he did but could not find my check. He did tell me lots of places where it was NOT.
I spent about an hour on hold with the 401K management company today but lost my patience and hung up. About an hour later the new institution called with the news that they had my check. She knew the actual name of the 401K plan and the dollar amount, so she did have it. The USPS still shows it as missing in the "airport post office." Maybe I'll call off the search and send the hounds after my Mouser order. It will be a bit harder since the USPS claims that they never saw the package, and Mouser says that they shipped it on January 13.
Never trust USPS with anything really important. Overnight Fedex with signature may be one of the safest ways to send something, although you pay for the better reliability. UPS or Fedex ground is IME usually much more reliable than even USPS Priority mail. Around here we have neighborhood mail cluster boxes. Sometimes they put a piece of mail in a neighbor's compartment and mark it as delivered to me. The tracking shows it was delivered and there is no proof otherwise unless a neighbor happens to be kind enough to hand deliver the piece of mail.
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......And discussing new ways to profit by putting hard working people out of work. The same Wonder Boy was responsible for killing at least three airlines that called Miami their home when I lived in South Florida.
I am hesitant to mess with my high powered SCG breadboard until I can get some thermal pads with a good deal of voltage isolation, especially since I have no spare 1KV 6 Amp mosfets.