[Heath] The Heathkit IP-27

[MICHAEL TALLENT]

OK, I fixed my IP-27.  The DTG-600 and one of the 2N2869-2N301 pass 
transistors were bad.  I have several 2N2869's so I used them as 
replacements and the IP-27 works just fine and all the controls seem normal 
with no noise or ripple on the output up to 1 amp load.

I then put silicon PNP 2N5884 devices for Q1 and Q4-5 and put 2N2907's for 
Q2-3.  The supply worked but I was not able to get the current limit range 
to go beyond about 2/3's of full scale and the voltage range was shifted up 
somewhat as the minimum voltage that could be set on the lowest scale was 
about 1 volt instead of the .5 volt, but the controls did work normally 
within these ranges.  I did not adjust any of the cal pots, they may correct 
for some of these changes.  I think what needs to be modified is the current 
limit values to correct for the higher Vbe of the silicon devices, as 
expected.

For now I will put back in the Ge devices and use the supply.

I used my Heath IM-36 to test the transistors, worked great.

Mike T  W6MXV  retired circuit designer

----- Original Message ----- 
From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
To: "MICHAEL TALLENT" <mwtallent at comcast.net>; <Heath at puck.nether.net>
Sent: Thursday, June 07, 2012 9:12 PM
Subject: Re: [Heath] The Heathkit IP-27


> 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
>