[Elecraft] KPA1500 replacement devices

[Dynolab]

Hi Mike,
 
Agreed.
The ART1K6 looks like the best choice.
It is in fact one hell of an all around part!
 
I am curious if the pictures I attached in my last reply came thru as the Elecraft list administrator sent a message says my post had been rejected due to size?
If they did not show up, my water cooled amp using a pair of BLF189XR devices can be seen at:
https://www.youtube.com/channel/UCfPLagy3tyL164PjCmWUaqg
 
73,
Hal
W7YNC
 
From: M Cresap [mailto:m.cresap at yahoo.com] 
Sent: Wednesday, November 02, 2022 9:40 AM
To: Dynolab; Elecraft at mailman.qth.net
Subject: Re: [Elecraft] KPA1500 replacement devices
 
Hi Hal
 
I like the water cooling! I debated about using water cooling on a W6PQL 2 meter amp I built several years ago, ended up with an oversize heat sink instead.
 
Since the KPA1500 power supply probably can't safely be adjusted to 65 volts to best accommodate the ART2K0, the ART1K6 is likely the better choice since it is expecting 50 volt on the drain. An interesting experiment. 
 
Thanks for your perspective
 
73, Mike, W3IP
 
On Wednesday, November 2, 2022 at 01:13:46 AM EDT, Dynolab <dynolab at comcast.net> wrote: 
 
 
Hi Mike,
 
Agreed, the ART series does have lower Rth but I would still worry that it may not be low enough to make up for the increased saturation voltage and loss of efficiency due to a drain to drain impedance that has been optimized for a Vdd of 50Vdc.
However, I may be overly timid as I have a graveyard of LDMOS devices that did not survive air-cooled amplifiers.
I have since gone to water-cooling and don’t have to deal with the heat problems anymore. (See Attached)
 
73,
Hal
W7YNC
 
From: M Cresap [mailto:m.cresap at yahoo.com] 
Sent: Tuesday, November 01, 2022 3:21 PM
To: Dynolab; Elecraft at mailman.qth.net
Subject: Re: [Elecraft] KPA1500 replacement devices
 
Hi Hal
 
I see the Rds difference. Wouldn't the higher Rds be compensated by the better Rth (thermal resistance from junction to case) spec in the ART devices?
 
73, Mike, W3IP
 
On Tuesday, November 1, 2022 at 03:15:09 PM EDT, Dynolab <dynolab at comcast.net> wrote: 
 
 
While the higher voltage ratings of the ART1K6 or ART2K0 series looks very
attractive, it is extremely important to remember that heat is the number
one killer of LDMOS RF power FETs!
That being said, take a look at the specifications of the ART1K6 and ART2K0
and note that the Rds(on) drain-source on-state resistance of these devices
is significantly higher than that of the devices presently being used in the
KPA1500.
And this higher Rds(on) would result in higher drain-source saturation
voltage when the amplifier is running near its limits which would in turn
result in higher heat dissipation.
It is therefore possible that the ART1K6 or ART2K0 devices may be less
reliable than the devices currently being used in the KPA1500.
 
73,
Hal
W7YNC
 
-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of M Cresap via Elecraft
Sent: Tuesday, November 01, 2022 10:21 AM
To: Elecraft at mailman.qth.net
Subject: [Elecraft] KPA1500 replacement devices
 
Anyone have an educated guess whether the ART1K6xx or ART2K0xx devices would
be a drop in replacement for the currently used device in the KPA1500? Most
of the interesting specs are within 10% of the current device, the open loop
gain may be a dB or two higher (if the data sheets are really comparing
apples to apples). 
 
The main attraction of the ART1K6 and ART2K0 devices is the higher peak
voltage handling capability - 177 or 200 volts vice 135 volts for the
current device. Maybe a higher peak voltage capability will keep the
amplifier out of the repair shop due to external events like arcing baluns
or antennas flexing in the wind.
 
The package styles are identical, the ART devices are in stock from a few of
your favorite distributors, similar price to the current device, maybe the
quiescent bias voltage would have to be tweaked a bit...
 
73, Mike, W3IP
  
  -    
 
 
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