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Author Topic: HeathKit HP-1144  (Read 778 times)
W8RLC
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Posts: 127




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« on: October 28, 2018, 10:43:03 AM »

Heath made one change to the HP-1144 PSU that added the over voltage protection circuit, but I do not see, or rather should say, cannot find any other change orders or service bulletins for this item. Are any of you aware of any? If so can you email them to me?

73
Bob, W8RLC
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W9GB
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Posts: 3368




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« Reply #1 on: October 28, 2018, 04:45:31 PM »

Bob,

I do not remember an Over-Voltage Protection (OVP) addition to the Heathkit HP-1144 PSU.
HP-1144 Manual
http://pdf.textfiles.com/manuals/SCANNERS-F-R/Heathkit-HP-1144.pdf

There were some changes for the 1144A model, but I have not compared the two schematics/parts list in manuals.
HP-1144A manual
https://www.qsl.net/ve1za/Manuals/Heathkit%20HP-1144A.pdf

Some parts used in the HP-1144 are obsolete/discontinued, like the 6-pin Motorola MFC 6030 (adjustable voltage regulator).  Datasheet here:
http://k5jxh.com/SB104ss/6030-datasheet-jxh.pdf

This regulator was used in other Heathkit DC power supplies.
Consider the LM-317 or LT1083 for new replacement circuit.
https://electronics.stackexchange.com/questions/379752/redesign-circuit-to-use-lm317-instead-of-mfc-6030
=
Kees, K5BCQ would have noted a change/service note, on his Heathkit SB-104 web site.
https://www.qsl.net/k5bcq/sb104/sb104.html

Mike Bryce, WB8VGE did design an OVP, The Protector for the HP-1144(A) power supply.
https://forums.qrz.com/index.php?attachments/theprotector-pdf.339152/
« Last Edit: October 28, 2018, 05:01:26 PM by W9GB » Logged
W9GB
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Posts: 3368




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« Reply #2 on: October 28, 2018, 05:20:23 PM »

Bob,

In comparing the two manuals (original and “A” model from 1978),
it appears that Heathkit added an SCR (p/n #57-86, NL576A or SPS135) to the circuit,
as a Crow-Bar at +15.5 VDC.  This would trip the fuse in the HP-1144A model.
http://www.rsp-italy.it/Electronics/Kits/_contents/Heathkit/Kits/Heathkit%20HP-1144A%20ac%20power%20supply%20Manual.pdf

Cross-referencing the NL576A SCR is discussed, here in 2004
https://puck.nether.net/pipermail/heath/2004-March/016663.html

gb
« Last Edit: October 28, 2018, 05:24:43 PM by W9GB » Logged
W8RLC
Member

Posts: 127




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« Reply #3 on: October 28, 2018, 08:07:28 PM »

gb,

Thanks for the threads. I had not previously seen the OVP circuit designed by Mike Bryce, WB8VGE. The OVP circuit that HeathKit came out with as a modification to the HP-1144 and as the standard circuit in the HP-1144A works, but tends to take out a couple components when it triggers.

The MFC6030 can still be purchased but I am not going to pay $25-$30 for one. Fortunately both of my 1144's use the 78MGT4 series regulator which is available for just a couple dollars. But I am currently in the process of rebuilding one of the 1144's, that has bad filter caps, blown pass transistors and a couple components on the PCB. The SCR is also kind of expensive now, fortunately that is still good so I do not have to purchase one.

The other 1144 has a couple modifications and I was wondering if they were mods that were instituted by HeathKit. 
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