[ARC5] Some questions...transistors...

[Kenneth G. Gordon]

On 12 Jun 2017 at 12:11, Dennis Monticelli wrote:

> 
> Ken, 
> 
> My career was in the semi business.

Neat.

> Regarding Hfe.  That DC parameter is usually measured at a modest
> current level. I would not be surprised to learn that the high
> amperage beta is closer to what your originals exhibit at similar high
> amperage.  In any case 100 to 150 if not out of line at all if
> measured at 1A. 

OK. That takes care of that issue, then. I had suspected the same, but was not sure enough 
of my long-unused knowledge in such matters to trust it.

> Regarding replacement transistors that blow up.

Well, these were advertised as being real Toshiba 2SD797s, but were, instead, Chinese 
made fakes. I think they had something like a 2N2222 inside of the cases.

>  Yes, exceeding BVebo can rapidly degrade or 
> destroy a transistor but does your ICOM circuit really do that....put a negative voltage spike on the 
> transistors?

Highly unlikely, it seems to me.

>  More likely the SOA (safe operating area) of the replacements is no where near that 
> of the originals.  SOA varies a lot from maker to maker all bets are off with Chinese sources.  
> SOA is only stated in the performance curves section of the datasheet and most abbreviated 
> datasheets don't provide it.  BTW, a BVebo cannot be as low as 4V because the physics of the 
> transistor's construction would not allow it.  A true 4V breakdown would represent what is termed 
> a degenerate junction...not good for proper transistor action and only good for making zener 
> diodes.

Ah. OK.

In addition, I just took another look at the specs: they are not  Vebo, but simply Veb of 4 V

> Did you check out the NTE387.  It is listed as equivalent.  Actually it is heftier.  The only downside 
> (apart from price $37) is the relatively high capacitance.

No. I had not. What I had settled on were MJ802G transistors. I have attached PDFs of the 
specifications for both the 2SD797 and the MJ802G. From what I can tell, the MJ802G will 
sub except for that one parameter....but what do I know? :-)

I'll look the NTE387 up too.

One suggestion by some to replace that IC-2KLPS is to use one of those 48 V 1500 watt 
regulated supplies commonly used in the Telco industry, then crank it back to 40 VDC output.

Trouble with those is they are awfully big. Thus, I'd like to fix this IC-2KLPS for my buddy.

Thanks,

Ken W7EKB


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