[Heathkit] HP23A trouble

[Carl]

AKA the Dim Bulb Tester or poor mans Variac.

Carl
KM1H


----- Original Message ----- 
From: <sbjohnston at aol.com>
To: <heathkit at mailman.qth.net>
Sent: Saturday, October 24, 2009 12:54 PM
Subject: Re: [Heathkit] HP23A trouble


> >Have not tested the xfmr yet (I need some
>>bravery liquid before I do that, hi,hi).
> 
> You're probably kidding about the confidence fluid, but be careful - 
> the voltages in the power supply can kill.
> 
> I would test the transformer by powering it temporarily through an 
> incandescent light bulb.  In other words, put a light socket in series 
> with the hot lead to the transformer and screw in an regular old light 
> bulb.  If the transformer primary is shorted, the bulb will simply 
> light at full brilliance.  If the primary is OK, the lamp's small 
> series resistance will not make much difference, and it won't light 
> much or at all.  Then you can measure the secondary voltages and see 
> what you've got.  Nice safety measure.
> 
> Steve WD8DAS
> 
> sbjohnston at aol.com
> http://www.wd8das.net/
> ---------------------------------------------------------
> Radio is your best entertainment value.
> ---------------------------------------------------------
> 
> -----Original Message-----
> From: Carl <km1h at jeremy.mv.com>
> To: Dick KF4NS <kf4nsradio at verizon.net>; heathkit at mailman.qth.net
> Sent: Fri, Oct 23, 2009 1:19 pm
> Subject: Re: [Heathkit] HP23A trouble
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> Unless the diodes were mismarked or reversed they should work fine. 
> OTOH, I
> only use 1N5408's for just about everything due to their battleship 
> surge
> ratings and never had a failure. They are certainly cheap enough.
> 
> Id start by testing the xfmr with nothing attached to make sure there 
> is no
> damage. Then proceed with caution.
> 
> Carl
> KM1H
> 
> 
> 
> 
> 
> ----- Original Message -----
> From: "Dick KF4NS" <kf4nsradio at verizon.net>
> To: <heathkit at mailman.qth.net>
> Sent: Friday, October 23, 2009 2:04 PM
> Subject: [Heathkit] HP23A trouble
> 
> 
>>I recently replaced the diodes with 1N4007's and all was
>> fine......until yesterday. I fired it up with no load to record the
>> voltages and heard a loud pop. The breaker was tripped so far that it
>> reversed the spring contacts so would not reset. I opened it up and
>> popped the contacts back to the opposite position and tried again. I
>> did the usual visual inspection and the "initial tests" before trying
>> again. It tripped again so did my diagnostics and found all the new
>> diodes shorted.
>>
>> I realize that 1N4007's are rated at 1000V PRV but only at 1A. The
>> breaker is rated at 2.92A. Is there a preferred sub for the original
>> Heathkit diodes? The 125mfd caps are testing ok except C3 at 159mfd
>> and C4 is 115mfd. None are shorted.
>>
>> Have not tested the xfmr yet (I need some bravery liquid before I do
>> that, hi,hi). The breaker will be replaced with a slo-blow 3A ceramic
>> fuse and should be ok along with an ICL in the power lead.
>>
>> By the way, anybody have 4 100K 2W to sell me? The existing 10pct.ones
>> are all out of tolerance.
>>
>> 73, Dick KF4NS
>> St Petersburg, FL 33714 USA
>> Keep The Glow!
>>
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