[Elecraft] KPA1500 replacement devices

[M Cresap]

 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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