[Elecraft] KPA-500 270V ERR

Thu Aug 26 18:58:41 EDT 2021

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
>> 
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