John Curl's Blowtorch preamplifier part II - Page 2774 - diyAudio
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Old 18th September 2012, 07:38 PM   #27731
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Quote:
I used to do a lot of work with cooled charge preamps. At one point I was reading a paper in which, observing the drain current, the low-temp JFET resolved single-electron capture and release trapping-center events, which could be tuned by the back gate voltage
Are these pricey? Only one seemed particularly low noise, but for MM you now ground the gate and bias/feedback to the back gate. Don't know if this would be a curious use of an obscure device or downright useful.
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Old 18th September 2012, 07:42 PM   #27732
bcarso is offline bcarso  United States
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Originally Posted by hitsware View Post
FWIW it takes ~ 1/2 volt to turn on the laterals as
opposed to ~ 3 volts for the verticals .........
(maybe not important for this app) ?
Well, sure, for one thing, when used as source followers there will be less headroom with higher Vt parts when used as powerline filters.

The cool thing about the laterals I've seen is the relatively low currents at which they have a nearly zero temperature coefficient of gate-souce voltage, something that you reach in conventional DMOS at impractical power dissipations. When operated at relatively low currents everyday DMOS have larger tempcos than bipolars.
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Old 18th September 2012, 07:44 PM   #27733
bcarso is offline bcarso  United States
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Originally Posted by scott wurcer View Post
Are these pricey? Only one seemed particularly low noise, but for MM you now ground the gate and bias/feedback to the back gate. Don't know if this would be a curious use of an obscure device or downright useful.
Haven't checked Scott. These appeared long after my days at UCLA, it seems. In those days the NucSci folks were extracting 4416s from the cans, or in the case of Bell Labs getting chips and putting them in low-loss headers.
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Old 18th September 2012, 08:09 PM   #27734
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> The cool thing about the laterals I've seen is the relatively
> low currents at which they have a nearly zero temperature
> coefficient of gate-souce voltage,

Yesamundo ! For AB amps nothing else even approaches
their simplicity of use.
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Old 19th September 2012, 12:56 AM   #27735
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Quote:
Originally Posted by hitsware View Post
> The cool thing about the laterals I've seen is the relatively
> low currents at which they have a nearly zero temperature
> coefficient of gate-souce voltage,

Yesamundo ! For AB amps nothing else even approaches
their simplicity of use.
Just so that everyone knows, Semelab makes improved versions of the Hitachi (Renesas) lateral output devices.

However, Renesas just announced the EOL for the lateral MOSFET drivers (J76-9/K213-6). The last date to order is the end of this year. The last date for delivery is next June. I contacted Semelab and they will NOT make a replacement for these. So if you want some, buy them now. There will never be another similar part from any source, ever...
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Old 19th September 2012, 03:08 AM   #27736
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Thanks Charles, I did not know this, and I am designing with these devices.
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Old 19th September 2012, 04:21 AM   #27737
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> I contacted Semelab and they will NOT make a replacement for these

They never did, right ?
No other lateral TO-220
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Old 19th September 2012, 03:02 PM   #27738
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It will get even more difficult in future to make truly excellent linear audio designs by the lay public and even part time professionals. The parts simply will not be available, except for companies or people who have stored up the parts, like Ayre, anticipating this shortage.

Last edited by john curl; 19th September 2012 at 03:08 PM.
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Old 19th September 2012, 03:35 PM   #27739
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For completeness and maybe future discussions, I am posting a partial schematic of the 20 year old HCA-2200 MK-2, for people who might find one to fix up or to part out.
Attached Images
File Type: jpg 2200 MK2.jpg (254.8 KB, 161 views)
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Old 19th September 2012, 04:24 PM   #27740
RNMarsh is offline RNMarsh  United States
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Collecting a few spare jFETs and bipolars that are obsolete or soon to be stopped producing will become very useful when keeping the analog gear up and running and repaired in the future.
[I just bought several J79/K216 to add to my stock]

Last edited by RNMarsh; 19th September 2012 at 04:26 PM.
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