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Old 31st January 2003, 05:05 AM   #1
Shaun is offline Shaun  South Africa
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Default 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?

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Shaun
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Old 31st January 2003, 05:54 AM   #2
AKSA is offline AKSA  Australia
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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
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Old 31st January 2003, 08:21 AM   #3
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Default 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
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Old 31st January 2003, 01:25 PM   #4
Shaun is offline Shaun  South Africa
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Thanks for the info, Hugh.

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Shaun
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Old 3rd February 2003, 10:12 AM   #5
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Default 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
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Old 3rd February 2003, 10:31 AM   #6
Shaun is offline Shaun  South Africa
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Default 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
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Old 3rd February 2003, 10:32 AM   #7
AKSA is offline AKSA  Australia
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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
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Old 3rd February 2003, 02:04 PM   #8
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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
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Old 3rd February 2003, 02:36 PM   #9
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Just found out they tell you if a part is out of stock! Anbody have experience with bdent?
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Old 7th February 2003, 09:02 PM   #10
mlloyd1 is offline mlloyd1  United States
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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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