kevin gilmore

ST does not have a fab in china. but they do have a back end site in china where the silicon is cut up and packaged. so the box says made in china. Wolfspeed (formerly cree) also uses a back end site in china. which is why the c2m1000 is stamped china.

that box is 1000 pieces. the mouser price for that is $283. i cannot imagine fakes for prices that low. fake 2sj79 are going for about $15 each. which is why there are tons of fakes on ebay. the typical hfe of 200 is the only spec on the datasheet. no minimum or maximum hfe specified.

the 3rd one is the only one with the box after the cree label that matches parts i have. my parts mostly have a w13814 date code

Note, not my soldering job. battery in microscope dead too much work to get the 1:1 lens out.

i just looked at what i had in stock. F405 and F413. both work fine. logo looks printed on. not etched and not stamped either.

probably easier to change the cathode resistors on the current sources.

mauser was legit. went bankrupt more than 10 years ago. they produced firearms. german manufacturer. mouser is definitely legit. never got a fake part from them yet.

so more than a few people are getting clobbered with 300b that don't even come close to the original published western electric document. of the 7 different varieties i have, only the original 1960's manufactured western electric comes even close to the spec. and the new western electric tubes come in low vgk and high vgk versions. (The B series tubes) just means you have to mess with the resistors. and yep its a major pain in the ass. the el34 original version pretty much worked +/- a few volts no matter what tube you stuffed in there as long as they all from the same manufacturer. or build a megatronxxl now known as optimus-prime. more money, but less of a balance problem.

get yourself a high voltage transistor tester and make an adapter board or solder wires to test subject. in this case it absolutely has to have a breakdown voltage of about 640. but in any case >600 the second part is likely genuine. no one is going to pirate a $1 part. the big hfe change i am beginning to see more and more of.

150ma for -60 50ma for -250

150ma spec for +/-500 50ma spec for +/-250 150ma spec for -60 50ma for +/-15

quotting shawn "I have some concerns if two modules can work in parallel. In Megatron XL, the two 300Bs per channel share the same filament supply" no they do not. each output tube (all 4 of them) has its own filament supply. they have to be seperate supplies for the 300b because they are in the audio circuit. in the d&g i use 2 switching modules in series to get the equivalent for 10v.

so that chassis in various sizes was available on ebay. i do not know whether it is still available. will have to look later. i know that some people think the tent labs filament supply is gods gift to dht tubes. real fact is that it does not really like hanging off -450v. as it was never designed to do so. there are better, cheaper and smaller ways of doing this.

you are aware that you need a heatsink touching all the sot transistor. still with heatsink it typically can take about 5 minutes to reach high temps.

i am aware of the overheating issues. i have an assembled board coming to me to look into this. something clearly has changed from the original parts i used and there is some positive thermal runaway that did not happen with the prototype. there is a later version board now, 4 layers, still does not fix the problem. putting 12v zeners in series with the 1.1meg resistors may introduce enough negative thermal compensation. otherwise the bias needs to be trimmed a lot. hate the parts situation i do.

can't find any internal pictures. but a 6ca7 as a current source for a 300b has plenty voltage swing, more than 1600 volts is possible. but the front end is lacking in voltage gain. so you are definitely going to need one of those 10v output dacs.

you forgot the dn2540 cascode on the 10m90s

updated board file, 10k input resistors added (optional) and 25k changed to 17k cfaelectrostatschem2-4 - CADCAM.ZIP

the neutrik jacks i used in the diy t2 are actually 4 wires. the connector shell is a seperate wire. i put in a jumper to chassis ground for that wire.

relays are dual coil latching. so 2 might be tricky. 3) lots and lots of cheap transistors. best to go with the "B" versions, matching is always better. 4) 50k attenuator NOT NEEDED. thats the point. there is no commercial product with an output voltage that will saturate the input. 5) very much like the ayre kx-r. individual resistor goes between the 2 pins. for increased gain should you want or need it. schematc shows everything at 0db gain.

only need one power supply for both channels and its not a lot of power. also runs whatever microcontroller you decide to use.

possible final version, 4 inputs and the xlr jacks correctly located preamp2025i - CADCAM.ZIP

this version should be compatible with the amb lcduino software with no changes. preamp2025h - CADCAM.ZIP

soren asked for the board with onboard grlv preamp2025g - CADCAM.ZIP preamp2025g.PDF

for clarity this board is mono. 2 required for stereo. boards stack. needs arduino software, or equivalent programable controller.