[Lowfer] Lowfer Final Transistors-Switching Time

LEE BAHR pulsarxp at embarqmail.com
Thu Aug 5 00:05:20 EDT 2010 

Hi Bill;

Where do you place these extra base diodes from/in your article?

As for the Lowdown.  (I hope this doesn't upset too many people).  I was a 
member way back when the publication was new.  It was great.  Something for 
everyone.  Reports plus lots of technical stuff, every month.  I looked 
forward to getting my new issue every month.  Since then,  I joined it a 
couple times but there is hardly any technical stuff, so I dropped out twice 
now.  The only thing I would see is month old station reports and beacon 
reports.  The LWCA internet site basically tells you to go to other URLs for 
info.  I know there are a lot of good guys as members, but I would think the 
club or publication would offer more through them rather then through their 
members.  With high speed internet, who needs station reports listed in a 
journal once per month.  It can be done instantaneously on the internet.  I 
just don't understand the LWCA or it's Lowdown.  Too me, the present LOWFER 
journal is the most boring thing I have seen and I love this lowfer stuff. 
(I know they rarely print something technical).  This list is great.  I 
remember when Ken Cornell had his Scrapbook and monthly technical stuff in 
the LOWDOWN.  Then there was Vince Pinto with new technical stuff all the 
time until he gave up the hobby and dissapeared.  His stuff was also in the 
LOWDOWN.  What happened?

(May I still stay in the group)?

Lee, w0vt




----- Original Message ----- 
From: "Bill Ashlock" <ashlockw at hotmail.com>
To: <lowfer at mailman.qth.net>
Sent: Wednesday, August 04, 2010 10:34 PM
Subject: Re: [Lowfer] Lowfer Final Transistors-Switching Time


>
>
>
>
> "Bill, where can I find your pp output circuit you mentioned today?  I 
> don't have LOWDOWN that far back."
>
> Don't feel alone, Lee, I never DID see the LowDowns with my articles 
> because I was not a subscriber at the time. (Hint, John? :) This should 
> get you a schematic of that circuit with some explanation:   Defining and 
> Refining the Lowfer TX Loop Antenna  BTW, check the plots of current gain 
> at increasing current in the data sheets for the 2N4401/4403 and the 
> MPS6602/6652. The MPS6602/6652 pair has higher current gain at currents in 
> excess of 200ma. It is possible, however, that the MPS6602/6652 is really 
> the same as the 2N4401/4403 but is (or was) computer selected for this 
> parameter. Also it IS important to balance the two halves in order to 
> reach the highest possible output power at 1W DC input power. You should 
> see a small glitch in the leading and trailing edges of the square wave 
> output where the cross-over in transistor conduction occurs. This should 
> fall half way on these edges. Invariably the 2N2222/2907 pair will be way 
> off in my circuit unless the balance pot is rotate
> d to one extreme.
>
> Bill
>
>
>
>
>
>> From: pulsarxp at embarqmail.com
>> To: lowfer at mailman.qth.net
>> Date: Mon, 2 Aug 2010 20:52:35 -0500
>> Subject: Re: [Lowfer] Lowfer Final Transistors-Switching Time
>>
>> I looked everywhere for 2N6601 and 2N6651 transistors.  Nowhere to be 
>> found.
>> These seem more unobtainable then MPS6602 and MPS6652.  However, you can
>> easily buy zillions of 2N4401 and 2N4403 transistors  for plus and minus 
>> 4
>> cents each.  I just ordered 200 each from Mouser plus a few NTE128 and
>> NTE129.  I also ordered a few Zetex ZTX653 and ZTX753.  I heard they 
>> worked
>> good, but getting educated on here regarding turn on and turn off times 
>> plus
>> saturation figures don't make the Zetex ones look good on paper. 
>> However,
>> we will see!  I bought a few of the Zetex anyway.  I'm trying to source 
>> some
>> MPS 6602 and MPS 6652 now.  I might get lucky but have not been given a
>> price for them to date.
>>
>> Bill, where can I find your pp output circuit you mentioned today?  I 
>> don't
>> have LOWDOWN that far back.
>>
>> Lee, w0vt
>> pulsarxp at embarqmail.com
>>
>>
>>
>>
>>
>> >
>> >
>> >
>> >
>> > Hi All,
>> >
>> > I spent a lot of effort to determine the best complementary output pair
>> > when I was experimenting with TX loop antennas for my loop articles 
>> > that
>> > appeared in the LowDown some 7 years (?) ago. The main requirement at 
>> > that
>> > time was that efficiency at a 1W DC input had to be as high as 
>> > possible.
>> > Normally a few percent loss in power would not result in much loss in
>> > transmitted distance covered but I didn't want to add another variable 
>> > in
>> > any of the very close loop comparisons I was making. I looked at the
>> > 2N2222/2907, the 2N4401/4403, the 2N6601/2N6651 and a number of 
>> > others -
>> > in fact any  switching transistors that I could get my hands on. Turned
>> > out the 2N6601/6651 was a cut above the rest in the output 
>> > configuration
>> > that appears in my second article. This circuit contains two additional
>> > base diodes from the popular Kohler circuit to reduce the collector
>> > conduction at saturation and thus reduce the power-eating turn-off
>> > transition where the transistors see both voltage and curre
>> > nt at the same time. I found that with the right transistors the
>> > efficiency of this circuit to be very close to 100% as measured both 
>> > from
>> > the RF and DC powers and the increase in case temperatures from 0 power 
>> > to
>> > a continuous 1W. The second place pair turned out to be the 2N4401/4403
>> > but the current gain at upper current levels did not hold up as well as
>> > the 2N6601/6651. The popular 2N2222/2907 was acceptable in most cases 
>> > but
>> > did not balance all that well in my circuit with the 2N2907 requiring 
>> > more
>> > base drive than the 2N2222. BTW, I found that using a Vcc in the area 
>> > of
>> > of 24 volts to be preferable over approx 12V because the collector 
>> > current
>> > is 1/2, and you will see faster switching times and less falloff of
>> > current gain at the upper current levels.
>> >
>> > The last time I looked for a source for the 2N6601/6651 I was 
>> > disappointed
>> > to find that ON Semiconductor (previously a part of Motorola) did not
>> > manufacture them. I found some other sources but the data sheets didn't
>> > exactly give me the feeling that these were the same device. I would
>> > appreciate knowing what luck others have had in finding these.
>> >
>> > Bill Ashlock
>> >
>>
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