On 2021-08-26 15:19, David Gilbert wrote:
Pedantic? If those were truly PIN diodes like you called them the
270v bias wouldn't have been used there.
Actually, I'm finding this interesting. So with real PIN diodes, you
don't have
to strongly bias them off?
The HV is obtained in various ways. W6JL does diode switching with a
tube amp, so he has ample HV available. My K2 has a crystal oscillator
feeding a toroid transformer and a voltage multiplier. Hans Summers
uses a voltage doubler running off the RF output of his amplifier. I
have heard discussions of people
using fluorescent ballast transformers.
A complication is that the voltage at a transmitter output - even though
it's nominal 50 ohms - can rise quite high with high SWR, especially in
the "looks like an open circuit" direction. So even though modern LDMOS
PA transistors are rated to tolerate extremely high SWRs, your equipment
is limited to the SWR that produces a voltage lower than the diode bias.
Hans Summers' design is elegant - since he's rectifying and multiplying
the RF itself, the DC is guaranteed to be higher than the RF itself.
Only thing is - there is surely a delay in creating that bias.
I will say that the QRP-labs approach somehow results in the cleanest,
most transparent-sounding QSK I've ever heard. Better than my K2. But
it's only one band, the selectivity is just ok, and it has no AGC...
- Jerry KF6VB
Dave AB7E
On 8/26/2021 2:56 PM, Fred Jensen wrote:
This morphed into a pedantic discussion of solid state diodes.
Chuck's original question was about the 270 V error. I'm fairly sure
the only purpose for the 270 V in a KPA500 is bias for the T-R
switch. He asked for suggestions. The T-R switch and the source for
the 270 V might be a good place to start troubleshooting.
73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County
On 8/26/2021 2:23 PM, David Gilbert wrote:
High voltage rectifier diodes would have very low doped N-regions,
which means fairly long carrier lifetimes so no doubt they work
somewhat like a PIN diode if properly biased. But they aren't really
the same thing, and I still say that a PIN diode has performance
advantages in many situations. They are more difficult and costly to
build, though.
I used to manage a large semiconductor entity that manufactured these
things.
73,
Dave AB7E
On 8/26/2021 2:05 PM, jerry wrote:
Using 1N4007's and 1N5208's ( I could have the last # wrong ) as
"Poor Man PIN
diodes" is pretty established practice in the amateur community.
Look up
W6JL on QRZ.com. He has an extensive article about it on his page
there.
Also Hans Summers of qrp-labs uses them in his 50W QSK amplifier.
Apparently, these kilovolt rectifiers behave very much like PIN
diodes,
at speed.
- Jerry KF6VB
On 2021-08-26 11:46, David Gilbert wrote:
That sounds odd to me. True PIN diodes are current actuated
devices.
The carrier lifetimes are long enough that the devices are "on"
even
if the signal peaks exceed the voltage of the control current ...
as
long, of course, as the control current exceeds the signal current.
On the other hand, I've heard that Elecraft has sometimes used
regular
switching diodes instead of PINs, and for those you need a voltage
that exceeds the peak voltage of whatever you're switching.
Both types of diodes have their place ... using one where the other
works better is not good practice.
73,
Dave AB7E
On 8/26/2021 11:33 AM, Fred Jensen wrote:
I think the 270 V circuit is DC bias for the PIN diodes in the
TR-switch.
73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County
On 8/26/2021 10:32 AM, Chuck Chandler wrote:
My KPA-500 has been running great for several years. Recently I
noticed it
was making the occasional extra "click" or "thunk" upon powering
up or
down. Usually it would "click" when powered up and again when
powered
down, but recently a few seconds after the first click there
would be
another one, maybe more of a thunk sound.
This afternoon I turned it on and when I pushed the
Operate/Standby button
I got a fault light and the 270V ERR message on the display. The
menu HV
option shows 68.4V, varying a bit, on my 240V line. I put it on
the bench
and opened up the top cover. There is a smell of overheated
components,
maybe burnt but more like too hot.
I've submitted the contact form on the Elecraft support page. Any
suggestions? For now, I'm running barefoot...
73 de Chuck, WS1L
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft@mailman.qth.net
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to ab7e...@gmail.com
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft@mailman.qth.net
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to je...@tr2.com
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft@mailman.qth.net
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to arch...@mail-archive.com
