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Old 27th July 2012, 06:27 PM   #231
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Very similar to findings in PLH article. THanks for the info. Very cool.
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Old 27th July 2012, 10:56 PM   #232
LBHajdu is offline LBHajdu  United States
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Default Just a side note on one of the required parts

Iíve just notice something strange Mouser (Mouser Electronics - Electronic Components Distributor), there sort of like another Digikey, has 6,793 units of the 2SK170-GR(F) in stock. They have zero of the 2SK170-BLF in stock but they have 29,600 on-order of which they will receive 8,998 by 8/20/2012 and another 13,600 by 11/9/2012 (at least according to their web site). They donít have any of the p-type and have no plans to get any in. The manufacturer is Toshiba.

At first this seemed like good news, but then I got to thinking (fair warning I have a devious mind). Obviously Toshiba is not going to magically look under some table in there stock room and find these JFets sitting around in three month increments. Have they started up production again? I doubt Mouser got a really good deal on e-bay. And besides Linear Systems a much smaller fish has taken up the torch producing drop in replacements with the LSK170. They would have less competition in the p-type domain, however it would be a strange situation where one company makes one half of a complimentary pair and another makes the other side but it would still be excellent for the industry as well as DIY.

My guess (only my speculation) is Toshiba made a really big mistake discontinuing 2SK170 and 2SJ74. This is being shown up by Linear Systems filling in the gap in the market. What to do to avoid getting chastised by your shareholders? Leak quantities of the 2SK170 and drive Linear Systems out of business, then point to them and say we were right to discontinue those old JFets nobody wants or needs anymore. The 2SK170 sells for $0.48 in units of 250 and the LSK170 sells for $0.50 in units of 1,000. So if quantities of 2SK170 magically continue to appear market forces will make this inevitable.

Strange Iím normally not the conspiracy theorist type.
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Old 28th July 2012, 12:21 AM   #233
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by LBHajdu View Post
My guess (only my speculation) is Toshiba made a really big mistake discontinuing 2SK170 and 2SJ74.
ah, not even dust in their pockets

btw, did Toshiba actually make the devices themselves
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Old 28th July 2012, 02:37 AM   #234
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I'm fairly certain they did, otherwise the rest of the world would not have
such problem duplicating those parts.

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Old 28th July 2012, 02:42 AM   #235
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Quote:
Originally Posted by LBHajdu View Post
The 2SK170 sells for $0.48 in units of 250 and the LSK170 sells for $0.50 in units of 1,000.
Get 'em while you can.

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Old 30th July 2012, 01:33 AM   #236
vizion is offline vizion  United States
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How do you compute for power using current bias in single-ended amps like the Amp Camp ?

8 Ohms * (0.71 * 1.0A)^2 = 4 watts
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Old 30th July 2012, 03:48 PM   #237
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Your calculations would be correct if Q2 was a constant current source, but it's not.

Note how C2 is connected to the bottom of R3/R4. When Q1 increases it's current to pull the load negative, the voltage drop across R3/R4 increases, C2 couples this change to the gate of Q2 making it conduct less. Q3 also conducts more which reduces the Q2 gate voltage. When Q1 reduces current, the voltage drop across R3/R4 reduces. C2 couples this positive going voltage to the gate of Q2 making it conduct more. Q3 also sees this voltage drop, it conducts less until the current flow through R1/R2 and to the load increases to makeup the difference in voltage from the source of Q2 to the drain of Q1.

If Q2 was a constant current source and the bias was 1 Amp, Q1's current could go up to 2 Amps or down to zero Amps supplying +/- 1 Amp peak to the load. Because Q2's current changes to be the opposite of Q1, the load current could be +/- 2 Amps in theory. However, Q1 would be very non-linear, although distortion would be mostly even order. In this design, with an 8 ohm load, the amp runs out of voltage before it reaches +/- 2 Amps load current. Idle current could be reduced, but distortion would increase.
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Old 31st July 2012, 11:33 PM   #238
zany is offline zany  Australia
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any news on when the pcbs and parts kit will be available?
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Old 1st August 2012, 04:39 AM   #239
Variac is offline Variac  United States
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Ok, I've got the parts kits all bundled up and I'm really proud of them. They'll have everything required to make a functioning amp, including wire! Jason, diyFounder, was in town and helped out on some of the packaging. Of course we forgot a few things and are ordering them. The boards should arrive soon, I hope this week and will be added to the kits. Tragically I'm leaving town in a couple of days until the 14th of August. So within a month kids, can't do anything until the boards arrive.

Mark
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Old 1st August 2012, 10:40 AM   #240
zany is offline zany  Australia
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Thanks for the reply Mark, looking forward to it.

cheers.
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