IP-27 Restoration

[Alex]

Hi Gregory,

Got the Ip-27 up and running, it's working nicely now. Got it all cleaned
up and it almost looks as good as new. Bought 3 new binding posts and they
look very close to the original ones. Only thing I'm a bit disappointed
with the accuracy of the build-in voltmeter, depending on the range, it
seems to be 0.5 to almost 1 volt off at the upper part the range. In
general it also was reading a tiny bit low on all ranges, so I put a 1-meg
10-turn trimmer in parallel with each of the 3 voltmeter range 1% resistors
and calibrated then individually. Still if I calibrate any range around mid
scale, for example to 20V on the 50V range, when I go to the 50V mark on
the meter my DVM is only showing 49.1V. If I turn up the fine voltage adj
control to 50V on the DVM, than the needle has already passed and cleared
the 50V mark. Oh well, analog voltmeters. Anyway the error is really not
much, and one can always double check with a DVM in case an accurate
voltage is needed.

Other than that, I think its a great power supply. And the current limiting
function works like a charm. Very useful to prevent "smoking" test circuits.

BTW, never got to install the 500-ohm thermistor, I just left the 510-ohm
1/2w resistor in place. Just in case, to test thermal stability I ran the
supply at maximum current output to get it warmed up, and it was excellent.
I left it running with a 1.5Amp load for about 30 minutes, and saw no
variation or runaway effect (common in Germanium transistors as they heat
up). In any case the back of the case, or the heatsink for that matter,
didn't really get very hot. I used two 2N2288 transistors for the series
regulator, and a OC-28 for the current limiter. I found these old TO-3
Germanium devices in one my parts drawers.

Next in line is a nice IP-17 HV Power supply I got at ebay. Still waiting
for it to arrive, and it's supposed to be in "working condition", as it was
still in service. At least that's what the seller claims. Well no reason to
doubth him, guess I will find out soon.

Alex

At 09:57 PM 9/9/2004, you wrote:
>Alex -
>
>So how is the restoration project going on the IP-27 ??
>
>g. beat
>w9gb
>
>----- Original Message -----
>From: "Alex" <temple-heath at LAVO.COM>
>To: <HEATH at LISTSERV.TEMPE.GOV>
>Sent: Wednesday, August 18, 2004 11:52 PM
>Subject: IP-27 Parts, Binding Posts & Cal Procedure
>
>
>>Hello,
>>
>>I'm restoring a IP-27 LV Power supply that I got back from a friend who
>>had
>>purchased it from me (used/non-functional) about 25 years ago. Got the
>>Heathkit bug and decided to trade it back for some work I recently did for
>>him. He never fixed it so it was pretty much in the same condition as when
>>I first got it at a flea market.
>>
>>Already got the power supply operational, thanks to a partial manual &
>>schematic from BAMA, and after replacing some parts: changed all 3 power
>>transistors (someone had put in Silicon ones) back to Germanium units (had
>>to use substitutes), replaced 4 electrolytic caps, and added a missing
>>zener. Still need the 500-ohm thermistor (it's missing), and the output
>>binding posts (two of them are just missing their respective red and black
>>plastic buttons, and the third one (green) is completely broken off, so
>>the
>>whole part will be needed.
>>
>>If anyone has a spare unit for parts, and is willing to part with the
>>binding posts (preferably in good condition) and/or the thermistor (Heath
>>p/n is "9-9"), I'll be more than willing to pay a fair price plus
>>shipping.
>>BTW, these same binding posts are also used on many other Heathkits. If
>>you
>>happen to have something that might fit my needs, please let me know the
>>model of the unit so I can make sure the parts are compatible. I know I
>>could just drop in any other generic binding post, but I'm kind of aiming
>>to get the unit back to it's original Heath look. Would also be interested
>>in buying the original power transistors, and maybe some other parts as
>>spares. If you can help, please just let me know what you have.
>>
>>Finally, if someone happens to know the correct calibration procedure for
>>this power supply (3 trimmers on the back of the unit), I'll be most
>>grateful to receive a detailed description. The manual I downloaded is
>>missing the calibration section. So far I only managed to "ballpark" the
>>unit's calibration, but would very much like to make sure I have it
>>"right-on".
>>
>>Thanks in advance.
>>
>>Regards / 73
>>Alex
>>
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Products bought, sold or traded here is the responsibility of the
parties involved.  This list and the City of Tempe are not responsible
for losses or misrepresentations of any kind.  Buyer beware!

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This list is a public service of the City of Tempe, Arizona
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To post - HEATH at LISTSERV.TEMPE.GOV
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