[Amps] Internal QSK-5

Sun Feb 1 14:51:20 EST 2009

Thanks again, Joe!

I suspect that the basic theory of operation is unchanged, but the 
hardware that implements the theory may be upgraded. I'll have to 
look on BAMA. Yes, Tom designed  the PIN-5 which became the QSK-5. It 
may be that I'll have to bite the bullet and replace the PIN-5 with 
its more robust progeny. Looking at the QSK-5 manual, I see that it 
incorporates the idea of a keying loop. Doing that guarantees that 
there's never any hot switching,

I['m most curious about the high-voltage FET you mentioned. There 
aren't any FETs in the PIN-5. The high-voltage transistor is a 
bipolar NPN 2N6740 which is good for about 650 V. Incorporating a FET 
may be one of the difference between the PIN-5 and the QSK-5, because 
if I recall correctly, the 2N6740 is being run at its max voltage 
ratings. I suppose that if Q3, a 2N6740 (in my schematic) is shorted, 
that might create some havoc...

73,

Kim Elmore, N5OP

At 11:02 AM 2/1/2009, Joe Subich, W4TV wrote:

>Kim,
>
>I was using the schematics for the QSK-5 at BAMA and comparing
>the functions to the DEO QSK-1500 that I was very familiar with
>a lifetime ago <G>.
>
>The PIN-5 should be very similar to internal circuit board in
>QSK-5.  If I recall, W8JI did the QSK-5 for Ameritron and then
>adapted the "guts" for the amplifiers.  The installation info
>for the "internal" versions of the QSK-5 should be of some help
>in matching the schematic/functions.
>
>Any pin T/R switch for an amplifier has three functions ...
>the transceiver to input path, the output to antenna path
>and the "bypass" path.  Even though the amplifier has a
>mechanical T/R relay you need the bypass path to provide
>quick restoration of receive.  In general the T/R relay is
>put into the "transmit" mode when the amplifier is taken
>out of standby and the diodes to all the switching ... you
>will notice that one of the high voltage FETs is used to
>switch bias in the amplifier ...
>
> > There was no internal arc in the amp -- I had a failure out
> > at the antenna that resulted in a big mismatch that blew the
> > fuse lamps.
>
>This happens because the RF voltage gets higher than the
>reverse bias in the "receive" path.  The diodes are no
>longer cut off and they begin to conduct.  If the voltage
>gets high enough, the diodes or the control circuit (one
>of the transistors) can be damaged.  The reverse voltage
>rating of the diodes can be exceeded even without an external
>arc.
>
>73,
>
>    ... Joe, W4TV
>
>
>
>
> > -----Original Message-----
> > From: Kim Elmore [mailto:cw_de_n5op at sbcglobal.net]
> > Sent: Sunday, February 01, 2009 11:17 AM
> > To: lists at subich.com; 'amps'
> > Subject: RE: [Amps] Internal QSK-5
> >
> >
> > Thanks, Joe!
> >
> > I stand corrected, especially after I renewed my memory looking at
> > the docs I have.
> >
> > This is an early PIN-5 switch (S/N 0018) and it came with minimal
> > documentation. Do you know what the difference are between it and the
> > QSK-5? Is it all the same with upgraded components, of have there
> > been other changes? If I understand your description correctly, there
> > must be some difference because you mention there is a "bypass"
> > function in the QSK-5, which does not exist in the PIN-5. The PIN-5
> > depends on what had been the T/R relay in the amp for the bypass mode.
> >
> > There was no internal arc in the amp -- I had a failure out at the
> > antenna that resulted in a big mismatch that blew the fuse lamps.
> > Ideally, the fuse lamps protect the rx PIN diodes by blowing before
> > they do, but it may have been a case of both failing. I'll check. them
> >
> > 73,
> >
> > Kim Elmore, N5OP
> >
> >
> > At 10:12 PM 1/31/2009, Joe Subich, W4TV wrote:
> >
> > > > Recently, though, I had some 160 m antenna
> > > > problems under high power and blew the fuse lamps that
> > protect the
> > > > rx PIN diodes.
> > >
> > >Wrong ... the fuse lamps protect the transceiver if the
> > "receive" PIN
> > >diodes or HV power supply fails and amplifier RF gets
> > through. They are
> > >also there to prevent the amplifier from running away in the
> > event of a
> > >diode/HV failure.
> > >
> > > > I'll check the schematic, but does anyone have an idea or
> > two about
> > > > what might be going on?
> > >
> > >Check D2, D3, D4 and D11.  Also make sure that the high voltage is
> > >present on L6 in transmit.  Flashing of the fuse lamps
> > indicates that
> > >RF is getting back from the output of the amplifier to the
> > transceiver.
> > >D2/D3/D4/D11 should be reverse biased (through Q3) in transmit and
> > >forward biased (through D6 and Q4) in receive.
> > >
> > >If you had a high SWR or arcing situation, I would expect D4
> > and D11 to
> > >short and significantly impair the isolation between the antenna
> > >(amplifier output!) and transceiver during transmit!
> > >
> > >In the QSK-5, D1 is the normally open path from transceiver
> > >to the amplifier input (drive).  D2/D3/D4/D11 is the normally closed
> > >(amplifier bypass) path between the transceiver and the antenna, and
> > >D7-D10 are the normally open path from the amplifier output to the
> > >antenna (RF Out).
> > >
> > >73,
> > >
> > >    ... Joe, W4TV
> > >
> > >
> > >
> > >
> > > > -----Original Message-----
> > > > From: amps-bounces at contesting.com
> > > > [mailto:amps-bounces at contesting.com]
> > > > On Behalf Of Kim Elmore
> > > > Sent: Saturday, January 31, 2009 8:55 PM
> > > > To: amps
> > > > Subject: [Amps] Internal QSK-5
> > > >
> > > >
> > > > I have an AL80A with an internal QSK 5 switch (one of the early
> > > > ones) that I've had since new (S/N 095). For well over 20 years,
> > > > it's been working flawlessly. Recently, though, I had some 160 m
> > > > antenna problems under high power and blew the fuse lamps that
> > > > protect the rx PIN diodes. Blowing these is no biggie as it's
> > > > happened before when I mis-selected an antenna or has a
> > switch set
> > > > wrong. I replace them and go on my merry way.
> > > >
> > > > WIth K3LR's help, may 160 m antenna seems to be going
> > again. So, as
> > > > a final smoke test, I stated testing it under high power.
> > But, this
> > > > time I'm seeing the fuse lamps light up when I transmit with more
> > > > that a few hundred watts on 160 m into a dummy load. I don't see
> > > > this on 80 m or any of the higher frequencies. As far as I know,
> > > > this is new, though I've never had much of a 160 m antenna and so
> > > > didn't use the amp it much down there.
> > > >
> > > > I'll check the schematic, but does anyone have an idea or
> > two about
> > > > what might be going on?
> > > >
> > > > 73,
> > > >
> > > > Kim Elmore, N5OP
> > > >
> > > > _______________________________________________
> > > > Amps mailing list
> > > > Amps at contesting.com
> > > > http://lists.contesting.com/mailman/listinfo/amps
> >