[Amps] Advice needed for SS amp

[Alex Eban]

No, the problem really lies with the devices.
I used a pair of these devices from AR and they took a lot of abuse without
complaints!
I heard from local sources that microsemi have problems with voids in the
bond -when attaching the dies to the header- they still can't handle the
peculiar package.
If you get off the high voltage verion you might as well switch back to
classics like the MRF 157 et al, but then you won't get anything new done!
Alex	4Z5KS

-----Original Message-----
From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of MU 4CX250B
Sent: Thursday, June 06, 2013 4:43 AM
To: Paul Decker
Cc: amps at contesting.com
Subject: Re: [Amps] Advice needed for SS amp

Seems to me the 50V limit would be a deal breaker.  I love the idea of a
transformerless design. I wonder if the THP problems were really the
devices, as opposed to a design glitch they never figured out.
73,
Jim W8ZR

Sent from my iPhone

On Jun 5, 2013, at 6:45 PM, Paul Decker <kg7hf at comcast.net> wrote:

> Hi Bill,
> I had an amp using the MRF1500 parts, based on the commercial  Tokyo high
power design.
>
> I also talked to the THP guys for a while at Dayton and they are phasing
out their ARF1500 design using the Microsemi.  The reason I was told is
because of quality issues with the parts themselves.
>
> IMHO, it may be better to go with the NXP BLF578XR since it is a 1500W
part although it is only 50V.
>
> Paul,
> kg7hf
>
>
>
> Message: 1  Date: Wed, 05 Jun 2013 09:07:14 -0700  From: Bill Turner   To:
Amps   Subject: [Amps] Advice needed for SS amp  Message-ID:   Content-Type:
text/plain; charset=us-ascii    I'm thinking of building a solid state 1500
watt amp using some of  MicroSemi's high voltage MOSFETs. This is a new kind
of project for me and I  would appreciate any comments you might have which
would help me avoid any  blunders.    The MicroSemi ARF1500 looks attractive
because of its high power  capabilities and relatively low price. Digi-Key
carries these for $205 each.  A single one is rated at 750 watts output so I
would use two of them. I'm  thinking of water cooling.     MicroSemi data
sheet is at  http://www.microsemi.com/existing-parts/parts/81770 and there
are other  versions with similar ratings.     Notice the unusually high
power supply voltage. I'm thinking of running a  full wave bridge rectifier
directly off the 240 VAC line, thus eliminating  the power transformer and
giving
  about 340 VDC
>  no-load. The amp would have  to be isolated from ground of course, with
input and output coupling via  toroid transformers and PTT switching done by
a well-insulated relay.     A set of four 10 amp 600 PIV diodes is available
on eBay for less than $30  and a 6800 uF 450 VDC capacitor is available for
about $50 including  shipping. There's most of your power supply. Pretty
cheap, huh?   :-)    Of course with that size cap a step-start circuit would
be mandatory lest  you blow your main house breaker when you power up.    My
main use would be RTTY and CW so linearity is not an issue, but do you  have
any thoughts on what the IMD might be for SSB? I can't find any data on
MicroSemi's website for that. Maybe it's no good for SSB.     Since the
output impedance is about 50 ohms, I'm wondering if a 1:1  broadband antenna
balun might serve for the output toroid? Just a thought.  Might not be a
good idea.     Like I said, I'm a complete newbie at solid state amps so all
comments 
 are  welcome. Th
> is almost seems to be too easy to be true. Go ahead, burst my  bubble.
:-)    73, Bill W6WRT
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