[Amps] Internal QSK-5

[Joe Subich, W4TV]

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
>