See the below info re the*K3* LPA final FETs.
There were some changes when the devices went not available.
And now they are phasing out the newer device and we are building our own.
_The *K4* uses the newer one, -G5_. HOWEVER, the legs are bent in the
opposite direction!!
They are likely to break if flexed the other way!
I would get them from RFParts.com vs disabling a K3.
https://www.rfparts.com/rd15hvf1-501.html
In any case, the _biasing routine must be run_ with a command, and you
have to WAIT until you get the confirmation response otherwise it gets
all fubar.
Is this for #1743 that I replaced the KPA4 finals in Nov. 2024?
The kickback from an amp usually damages the LPA, but can damage the KPA
also (K3 and K4).
I will get the biasing info if you are going to replace them yourself.
You could also just send in just the KLPA4 since your K4 needs no updates.
Keith WE6R
*_LPA Finals, Q4 & Q5. Old vs New device usage._*
*_Here is the info on the E580047, It has been replaced with E580085,
But see below for usage.
_*RD15HVF1 now comes in two variants; (the old one is no longer being
made, supplies limited).
RD15HVF1-101 -G is _the OLD one with marking "-G" on it Elecraft part
E580047_
(These are the final power transistors in the LPA, KLPA3A, K144XV, KX2 &
KX3).
RD15HVF1-501 -G5 is the _NEW one with marking "-G5" EPN E580085_
(It is used on the KLPA4) It is going away also, Elecraft is working on
it’s own replacement.
_To use the new -G5 on a KLPA3A_ (New LPA with just 2 devices);
Change R24 to 51 ohms E500269 , You MUST replace both FETs to NEW
type!!You MUST rebias!!
(Voltage on the gates is 4.02V)
To use the NEW device on an Old LPA (the LPA with 3 devices); It works,
no mods,BUT you must replace BOTHand you *MUST* rebias!!!
On 3/27/2025 11:31 AM, Robert Hayes wrote:
Hi Keith,
I don't think so. Everything worked fine during the NA SSB Sprint on
Saturday evening and I was using the amplifier. Then when I went to
use it Monday I noticed the power output was lower.
But based on what I am seeing it does appear to be the LPA. If it was
an issue with some sort of RF Energy Kickback and I was using the
amplifier with the output set to 100 watts, would it really damage the
LPA and not the HPA? Regardless, I will either need to swap out the
LPA itself or replace the transistors in the LPA I have here, which I
am happy to do. Is the transistor different from the ones used on the
K3 LPA? Since I have some K3's here I could grab one out of them in
the short-term.
Any other ideas or suggestions for repair?
73 Bob KW8N
On Thursday, March 27, 2025 at 01:33:53 PM EDT, Keith Trinity WE6R
<ke...@elecraft.com> wrote:
Hi Bob;
Did you have an "event" with an external amplifier? Like transmitting
with no load causing an oscillation and "kick-back" of RF energy back to
the K4.
I see you confirmed the LPA is damaged and posted on the groups.io forum.
Keith WE6R K3/K4 Tech
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