[Heath] The Heathkit IP-27

[Kenneth G. Gordon]

On 7 Jun 2012 at 12:40, MICHAEL TALLENT wrote:

> Guess I am going to clean off all the stuff on my IP-27 and start checking 
> it out.  See more comments below.

Got it. Thanks.

> > Q-1 is really weird: it is a DTG-600.
> >
> > Q-2, and Q-3 are either 2N2553 or 2N301
> 
> The 2N2553 is a small transistor NOT a 2N301.

Yes. My mistake, and thanks for the correction. See below. I have been battling a significant 
flare-up of my rheumatoid arthritis and am making many serioius mistakes lately due to both 
the medication and the very high pain levels. My apologies.

> I have a lot of older transistors so I would probably start by trying a 
> 2N3645 or 2N(PN)2907A

Well, I don't have any older transistors here at all.

> > Q-4 and Q-5 are 2N2869.
> 
> The 2N2869 is the same as a 2N301, I have some and they are marked with both 
> numbers, and are the large TO-3 case size.

Yes. Here is where I MEANT to add the 2N301

> > For the 2N2553, the TIP-32AG looks very good.
> >
> > For the 2N2869, the Fairchild FJAF4210-OTU is almost identical other than 
> > being Si.
> 
> The 2N2869 is used for Q4,Q5 the TO-3 size series regulators and I would 
> think that the TIP-34A would work here,

Sounds good. I'll add that to my list.

> the TIP-32A would work but is 
> smaller in size to mount into a TO-3 socket.Also a 2N3791 or 2N3792.

Scratch the TIP-32A from here: I meant it only as a possible sub for the 2N2553. Even so, I 
would mount a heat-sink on it.

> > For the DTG-600, there are two possibilities: 1) the SDSG-200 or 2) the 
> > TIP-36CG
> >
> > I suspect that the reason the DTG-600 was chosen for that particular 
> > circuit (current limiter)
> > was that for the time it had a fairly high hFE: min was 65 and max was 
> > 300, and therefore
> > would react quickly.
> 
> Hfe is the DC current gain and has nothing to do with "quickly".

Of course: again, my mistake. Thanks for the correction.

>  Maybe you 
> mean the Ft, but I don't think it matters in a DC power supply as you have 
> all these big capicators so nothing is going to happen very quickly.

Well, the purpose of the DTG-600 is to limit the current, and in that particular part of the 
circuit I suspect that large capacitors would have very little if any effect on transients.

> > The SDSG-200 (which is a Darlington pair) has an hFE that can be MUCH too 
> > high: like 15K
> >
> > The TIP-36CG has a typical hFE of 45, but max is about 600.
> 
> The 2N3791 should also work here but you will probably need to change some 
> resistor values in the current limiting circuit because of the higher Vbe 
> voltage of the silicon.

Yes.

According to Ken Simpson who maintained a bunch of these when he was working at a 
school, he could find no sub for the DTG-600 that would really work in that circuit. A sub 
would "appear" to work, but wouldn't really limit the current properly. I was reviewing the 
characteristics of the DTG-600 and could discover nothing apparently much different from 
the other Ge transistors in that PS except the hFE: the DC current gain was much higher 
than any of the others. Therefore, I figured that was what was different about it. vs the others 
and perhaps was why it was chosen for that particular service.

I'll have to do some more studying...

Thanks again for the corrections.

vy 73,

Ken W7EKB