VAS transistors

[ChocoHolic]

Hi Everybody !
May be I am just ignorant and did not find the relevant
threads....

But I am not succesful in looking for high end VAS transistors.
For the output stage there are often often mentioned:
2SC2922 & SA1216 (BJT)
MJL4281A & MJL4302A (BJT)
or in MosFet designs 2SJ201 & 2SK1530...

But for the VAS I am missing comparatively high rated
transistors (mainly looking for BJT here).
Isn't there something like 200V/2A/20W/200MHz/gain200 ??


Also for the input stage I am missing 120V/100mA/1W/1GHz/gain500....

Any hints or proposals are welcome, you don't need to meet my dream specifications.

Bye
Markus

[mastertech]

200Mhz at 2A at 200hfe wow sounds that you need to look in
some rf power transistor manuals, good luck

[rtarbell]

For the MJL4281 and MJL4302, you can order free samples from ONsemi.com. They are usually really good at fast orders, and you can order up to 25 of each at no charge (but include $11 for shipping).

For small signal BJT transistors, I'm not sure if this is what you're looking for, but I like to use Zetex FZT857 (npn) and FZT957 (pnp). They are surface mount packages rated at 3 watts, 350V breakdown. Digikey has these.

[jacco vermeulen]

Markus,

if you have a source for devices that do 200V/2A/20W/100MHz/100 gain,that are also obtainable, you can make me a happy bloke.

How about something affordable, and still on this planet:
Sanyo 2SA1606/2SC4159

[aparatusonitus]

For VAS BF469/470/471/472, or BF871/872 are probably one of best you can find. Now obsolete, but anyway. Have some sugestion from Toshiba, Hitachi, Panasonic and Sanyo, but I am at work right now, can't remember the numbers

[AKSA]

For a VAS, my work has shown you don't need more than 200MHz, 50mA and beta 150. A parameter of importance is Cob, the base/collector input capacitance, which should be under 3pF if you can find it. However, going higher in speed could well cause more problems with stability, and making an amp stable with lag compensation appears to have sonic repercussions across the entire audio range.

Toshiba have devices which are tailored to VAS audio duties.

Hope this is helpful,

Hugh

[mzzj]

Originally posted by ChocoHolic
Hi Everybody !

But for the VAS I am missing comparatively high rated
transistors (mainly looking for BJT here).
Isn't there something like 200V/2A/20W/200MHz/gain200 ??

How about importance of Early voltage? VAF*Hfe is some sort of benchmark in semiconductor processes. Or how about VAF*Hfe*ft multiplied by voltage rating ?

there seem to be general tradeoff between VAF and Hfe in similar transistors like BC550A or BC550C

Heterojuction transistors might be the way to go, but these RF-devices are usually low-voltage. Might be usefull for input stage if you cascode it to reduce voltage on input transistors...

[Ultima Thule]

Hi Markus,

of an occasion I found these earlier today when looking around which happens to be quite close to your match...

Panasonic 2SA1535/2SC3944

180V/1A/15W/200MHz/hfe90-220

Cheers Michael

[amplifierguru]

Hugh is right here - the Vas is typically the dominant pole in the conventional (ugh) topology and, widebanding it only means you need to apply extra compensation (with it's associated degradation of PSRR and loading) or stability will suffer.

Best to have no Vas thus eliminating the dilemma of which exotic device to use.



Cheers,
Greg

[mcp]

Hello Markus

Toshiba 2SA1930 / 2SC5171 may be worth looking into.

180V / 2A / 20W / 200MHz / hFE 100-320

Isolated TO-220 packing too.

Regards