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-   -   Choices for Vas transistor (http://www.diyaudio.com/forums/solid-state/10566-choices-vas-transistor.html)

Shaun 31st January 2003 05:05 AM

Choices for Vas transistor
 
Hi

What are the implications of substituting a video amplifier transistor such as BF871 in place of a MJE340 as a Vas transistor? Would the Cdom have to be changed?

Regards
Shaun

AKSA 31st January 2003 05:54 AM

Hi Shaun,

Video transistors are good in this roll.

Cdom need not be changed, BUT it may be gainfully reduced.

A very good one to use is the Sanyo 2SC3955, a 300MHz beast with impeccable specs and collector capacitance of just 1.8pF.

Cheers,

Hugh

jan.didden 31st January 2003 08:21 AM

Vas xsistor
 
Hugh,

Those Sanyo's look pretty good indeed! Normally these types have relatively low Hfe, but these have groupings going up to 160 min.
Thanks for the tip.

Jan Didden

Shaun 31st January 2003 01:25 PM

Thanks for the info, Hugh.

Regards
Shaun

capslock 3rd February 2003 10:12 AM

Sanyo source?
 
Dear Hugh,

I also like this Sanyo series of video transistors. The problem is it seems to be discontinued, I even got that info in Japan.

While there is still a limited supply of the C3955, its counterpart 2SA1540 seems to be gone for good.

I can still get a pair from the same series that has a lower current rating, but it's no longer possible to order them from the same gain group.

Do you have a special source or know about adequate replacements?

Regards,

Eric

Shaun 3rd February 2003 10:31 AM

Move to surface mount?
 
In a brief search for high-voltage video transistors, I got the impression that most of these devices are now being offfered as surface-mount parts. I hope that there will still be leaded parts in circulation in the future...

Shaun

AKSA 3rd February 2003 10:32 AM

Hi Eric,

Well! I did not realize it was discontinued!! Bummer!

But it is available at www.pacificsemi.com (US46c), and www.bdent.com (US92c) in one off and 100+ quantities.

I made a list of transistors suitable for this work some time back but knowing me I've lost the damn thing.......

Sanyo has a proprietary manufacturing process which reduces collector capacitance, and frankly this makes them very desirable as VA devices.

I will seek out more; I buy from Peacock Industrial in Singapore and yesterday sent out an order. I'll let you know.

Cheers,

Hugh

capslock 3rd February 2003 02:04 PM

Dear Hugh,

thanks for your link. Pacific Semi has good prices, but you'll notice their stock is 0 for all of these parts. I have no idea whether that means the do special order only or if it's simply no longer available.

BD do not say whether they have stock.

Do you have any way of ordering parts form the same h_FE group?

Greetings,

Eric

capslock 3rd February 2003 02:36 PM

Just found out they tell you if a part is out of stock! Anbody have experience with bdent?

mlloyd1 7th February 2003 09:02 PM

Just to share some info....

I just got some 2SA1540 and 2SC3955 from MCM (in USA).

And no, I haven't checked to see if they are fake or not. :(

Both NPN and PNP were "D" grade. That means HFE @10mA range of 60-120.

FYI

mlloyd1

oops, I forgot: price was $1.15 and $1.07 USD (>15 pieces each) respectively


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