Fw: 136 IC Amplifier

[David Borden]

Gang,

   If anyone is interested in this little 24 watt amplifer, it costs $36 and
you order if from Canada using your credit card.  It comes in 5 or 6 days
and is easy to construct.  Below is the Kesteloot Hardware Testing
Laboratory report on the thing.  Maybe Andre will bring it to the Thursday
meeting for show and tell.  I will still be in Texas.  The URL for this
amplifer is:
http://www.qkits.com/
and it is the Maplin LU96 kit.

-----Original Message-----
From: Andre' Kesteloot <akestelo@bellatlantic.net>
To: Dave Borden <dborden@laser.net>
Cc: Terry Fox <tfox@erols.com>
Date: Sunday, July 04, 1999 16:35
Subject: 136 IC Amplifier, part II


>Hello Dave,
>Further to my previous msg. (see below),  I have now tested your
>amplifier with 48
>volts DC Vcc.
>Summary of the results:
>1) it performs somewhat better at 48 volts than at 24v, at least as
>far as
>distortion at 137 kHz is concerned,
>2) with 48 v DC Vcc, it does put out 28 watts @ 13 kHz, and 24 watts @
>137 kHz into
>a 4 ohm resistive load,
>3) as mentioned before, you will need to bolt it to a serious heat
>sink. Otherwise,
>the built in temp sensor turns it off.
>Congratulations on a good choice.
>Andre'
>********************************
>Andre' Kesteloot wrote:
>
>> Hello David,
>> Congratulations, this kit of yours is not bad   :-)
>> After a short test with 28 v DC  (I could try 48 volts later):
>> a) your amplifier works,
>> b) remember next time to use white heat silicone compound between
transistor and
>> mica washer, and between washer and heat sink,
>> c) your small heat sink (supplied with kit) must   _absolutely_  be
bolted to a
>> larger, serious one, as this thing heats up quickly (standing current)
>> d) it is almost flat to 136 kHz, so should be OK for what you want to do
>> e) the distortion at 136 kHz is hefty, but should not matter, as the
output of
>> that amplifier will be fed to a low pass filter (you have the design)
after the
>> 4 ohm / 50 ohm transformer (see below).
>> f) the amplifier has a slight tendency to oscillate, but I believe we can
cure
>> that with a few, well-placed capacitors.  (You may simply keep a box of
>> capacitors   _near_ the amplifier, on the bench, and that may well cure
it).
>> g) remember that you will eventually need a 4 ohm-to-50 ohm transformer.
I would
>> suggest you wind a T-200-3 core with #18 wire (from Frank Gentges?)
enough wire
>> on the primary to make Z at least (10 * 4) ohms at 136 kHz (see Amidon
tables),
>> then calculate the number of turns for the secondary to get 50 ohms,
>> h) I supplied you in the past two Amidon T-200-3 cores, which you will
need for
>> your output filter (double Pi low-pass filter). You will need an
additional,
>> similar core for your output transformer. Let me know if you want me to
bring
>> you an additional one next week.
>>
>> I do not have the time to perform any further tests now, and will be away
for
>> the rest of the week. Should return to McLean Saturday or Sunday.
>>
>> 73
>> Andre'
>> *********************************************
>