[Heath] The Heathkit IP-27

[Kenneth G. Gordon]

On 6 Jun 2012 at 12:59, Ron wrote:

> Yea, mine has been on the back burner for quite a while now  :-).

Well, we only have so much time. 
 
> Just two comments... First, I see no problem with using PNP Si 
> transistors. They
> are widely available and fairly cheap.

OK. I'll do some more research then.

> Second, assuming by Veb you mean Vebo (base-emitter junction reverse
> voltage max rating),

Yes, sorry. I didn't make myself clear here.

> it shouldn't be a problem.

Yes.

> For example, the
> 2N2905A, rating is 5V and it can readily be protected.

A properly placed zener should do the trick, similar to that mod that Heathkit 
provided for the IP-27 in a service bulletin.

> Another
> consideration could be Vbe (about 0.7V for Si vs. less than half that
> for Ge)

Yes, that is another problem which would have to be taken into 
consideration.

> -- but those depends on the circuit design, which I never got
> around to...
> 
> Have a nice day,

Thanks, Ron. vy 73,

Ken