sci.electronics.repair@googlegroups.com

Today's topics:

* Wall Warts - 3 messages, 2 authors
http://groups.google.com/group/sci.electronics.repair/t/de407a5056a54ee0?hl=en
* What kills a valve rectifier? - 2 messages, 2 authors
http://groups.google.com/group/sci.electronics.repair/t/3452d3f8314c6ded?hl=en

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TOPIC: Wall Warts
http://groups.google.com/group/sci.electronics.repair/t/de407a5056a54ee0?hl=en
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== 1 of 3 ==
Date: Tues, May 24 2011 10:36 pm
From: Jeff Liebermann

On Tue, 24 May 2011 17:03:17 -0500, Puddin' Man
<puddingDOTman@gmail.com> wrote:

>I don't think they really wanna
>honor the recall.

<http://www.cpsc.gov/cpscpub/prerel/prhtml03/03082.html>
Looks like the $25 rebate is all that they are offering.

Maybe calling them back and asking for the name of the company
attorney and whether this recall is defacto admission of their
responsibility if your garage burns down, might get their attention.

>>>Are there any guidelines for substituting these things? I'd like to keep the drill,
>>>but can hardly afford to burn the house down. :-)
>>
>>Not without knowing where the charge controller (probably just a
>>resistor) is located. If it's inside the wall wart, you'll need to
>>add an identical resistor. If it's inside the drill, you can probably
>>get away with your 12VDC substitute. Measure the current drain at the
>>charger output.
>
>Lost me there. Measure the *drain* at the charger output? But I'm
>pretty sure it is inside the buggered charger.

I guess it might be difficult to measure the current if the charger is
dead.

The problem is that we don't really know how the charging system works
without tearing it apart. If the blown charger has a resistor in
series with the output, there's no way to know at this point without
cracking it open, or comparing it with another working unit.

Start by using an ohms-guesser on the charger base. Cut the cord. Is
there DC continuity between the two wires and the contacts on the
charger base? If there's a measurable resistance, then the charger
base has either a resistor, or complexicated charge controller in the
base. I would therefore guess(tm) that the wall wart is just a simple
wall wart with nothing more complex than a thermal fuse inside.
However, if there is DC continuity between the leads and the battery
terminal connections, then the charge controller is inside the wall
wart, and a simple replacement isn't going to work.

Since the power supply is obviously blown and useless, tearing it
apart should reveal if there's anything inside. You'll probably find
a thermal fuse. If it's blown, just replace it with a similar thermal
fuse, glue the case back together, and continue charging. However, if
there's a series resistor inside (which is what I suspect), then use
the 12V adapter, add a similar resistor in series, measure the
charging current, and see if it's reasonable 0.1C. If not, adjust the
resistor value for 0.1C charging current.

>>My guess(tm) is you should have a mess of AA size
>>NiCd batteries inside the drill, which are usually rated at 750ma-hr.
>>Using the 0.1C rule, that would be a charging current of about 75ma
>>max.
>
>It's evidently all original: charger is 92950, power pack is 92955,
>and is a *sealed* unit. I see no way to take it apart.
>
>Am I missing something here?

Most chargers and charging bases are solvent welded together. They
can usually be cracked open with brute force. Place a masons chisel
along the glue line, and beat on it with a hammer. The glue line
should crack as the plastic bends. If not, just use a hack saw to saw
along the glue line. Do the repair, and then glue the case back
together.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

== 2 of 3 ==
Date: Tues, May 24 2011 10:44 pm
From: "Geoffrey S. Mendelson"

Jeff Liebermann wrote:
> Most chargers and charging bases are solvent welded together. They
> can usually be cracked open with brute force. Place a masons chisel
> along the glue line, and beat on it with a hammer. The glue line
> should crack as the plastic bends. If not, just use a hack saw to saw
> along the glue line. Do the repair, and then glue the case back
> together.
>

Overnight in a freezer helps. It makes the plastic brittle. If you have a deep
freezer (0F or colder) use it instead of a refigerator freezer (around 10F).

Geoff.

--
Geoffrey S. Mendelson N3OWJ/4X1GM
It's amazing how many people have no clue what the word "contiguous" means. :-(

== 3 of 3 ==
Date: Tues, May 24 2011 11:02 pm
From: Jeff Liebermann

On Tue, 24 May 2011 22:36:26 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

This is much too easy...

Skil 9.6v 92950 Battery Charger Repair 9.6 volt- 92955
<http://cgi.ebay.com/200454895811>
$13 plus $6 shipping.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

==============================================================================
TOPIC: What kills a valve rectifier?
http://groups.google.com/group/sci.electronics.repair/t/3452d3f8314c6ded?hl=en
==============================================================================

== 1 of 2 ==
Date: Wed, May 25 2011 12:20 am
From: "N_Cook"

spamtrap1888 <spamtrap1888@gmail.com> wrote in message
news:bd8dbf0e-9a3e-4397-a570-7af6541e38cd@d26g2000prn.googlegroups.com...
On May 24, 6:38 pm, "Phil Allison" <phi...@tpg.com.au> wrote:
> "Arfa Daily"
>
>
>
> >> What do you think about subbing the 5AR4 with a 5U4?
>
> > Never tried it, but looking at the specs, they look rather different
from
> > one another, see -
>
> >http://www.r-type.org/exhib/aaa0997.htm
>
> >http://www.r-type.org/exhib/aaa0504.htm
>
> ** Useless info.
>
> The big difference between the 5AR4 and the 5U4 is in amount of voltage
drop
> across each diode when conducting.
>
> The 5AR4 is uses an indirectly heated cathode, close coupled to each plate
> and the voltage drop is very low, about 35 volts at 700mA peak.
>
> The 5U4 uses a directly heated cathode with lotsa space between the plates
> and the cathodes - so there is a much bigger drop in voltage, more like
> 100 volts at peak current.
>
> So, if you drop a 5U4 in place of a 5AR4 - expect to lose 60 to 70 volts
DC
> straight off the B+.
>
> Also, the 5AR4 is rated to work reliably with a large filter cap on the
> cathodes ( 60 uF) compared to the 5U4 ( 40uF).
>
> So the proposed sub is bad news all around.
>

Considering that the vacuum tube rectifier was the first tube to be
eliminated (in receiving sets at least), why not replace it with a
semiconductor diode circuit? What effect would it have on the
amplifier's sound?

+++++

I totally agree a couple of 1N4007 and sag Rs would be fine by me but we are
talking musos here and the "valve sound" would magically dissappear. Of
course if I told them nothing about swapping to SS, the valve sound would
not disappear - strange old world isn't it.

== 2 of 2 ==
Date: Wed, May 25 2011 12:29 am
From: "Phil Allison"

"Nutcase Kook"

> I totally agree a couple of 1N4007 and sag Rs would be fine by me but we
> are
> talking musos here and the "valve sound" would magically dissappear. Of
> course if I told them nothing about swapping to SS, the valve sound would
> not disappear - strange old world isn't it.

** Just fit the diodes ( two pairs in series is a good idea ) and add
resistance only if it seems essential to do so.

he dud GZ34 can stay for ornamental value.

Tell the owner you fixed it.

BTW:

I fix lots of octal a valves, for bad soldering on the pins and flash burns
between plate and heater pins - even if it means removing the octal base to
do so.

Well worth it with newish 6550s, KT88s etc.

.... Phil

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