Re: Re: [Repeater-Builder] Re: 224 MHz PA fun and war stories

[Mike Morris WA6ILQ]

At 09:05 AM 07/16/07, you wrote:
>You have to lap the heat sink on the brick flat for impedence reasons.
>You still have to use heat sink compound to fill the gaps for thermal
>transfer reasons. It would also be nice to perfect the surface on the
>recycled Mastr II or Micor chassis to 50 um smoothness, but that would
>require a machine shop.
>
>The Science Behind It:
>http://www.downeastmicrowave.com/PDF/MOSFET%20PA_pdf.PDF
>
>The Power brick can be resurfaced by hand with sand paper and a piece
>of glass, I have done it, but I got metal poisoning for not wearing
>gloves or a dust mask.
>
>If any has ever owned a Yaesu FT-5100 or any radio that uses a SAV-27
>brick, they will understand the importance of having smooth and even
>surfaces when the substrate cracks in the brick and the module needs
>resoldering.

Likewise the S-AV17

Re: Re: [Repeater-Builder] Re: 224 MHz PA fun and war stories

[DCFluX]

You have to lap the heat sink on the brick flat for impedence reasons.
You still have to use heat sink compound to fill the gaps for thermal
transfer reasons. It would also be nice to perfect the surface on the
recycled Mastr II or Micor chassis to 50 um smoothness, but that would
require a machine shop.

The Science Behind It:
http://www.downeastmicrowave.com/PDF/MOSFET%20PA_pdf.PDF

The Power brick can be resurfaced by hand with sand paper and a piece
of glass, I have done it, but I got metal poisoning for not wearing
gloves or a dust mask.

If any has ever owned a Yaesu FT-5100 or any radio that uses a SAV-27
brick, they will understand the importance of having smooth and even
surfaces when the substrate cracks in the brick and the module needs
resoldering.

On 7/16/07, Ron Wright <[EMAIL PROTECTED]> wrote:
> To achieve a good heat sink coupling/bonding of 2 surfaces this is what heat 
> sink compound is for.  Just having a smooth surface does not insure a good 
> bond between 2 surfaces due to different flatness/shape.
>
> I wonder in any Mitsubishi power bricks mounting instructions what they 
> recommend.  Is its surface being used for any RF connection.  I hope not, not 
> good engineering.
>
> 73, ron, n9ee/r
>
>
>
>
> >From: DCFluX <[EMAIL PROTECTED]>
> >Date: 2007/07/16 Mon AM 12:12:13 CDT
> >To: Repeater-Builder@yahoogroups.com
> >Subject: Re: [Repeater-Builder] Re: 224 MHz PA fun and war stories
>
> >
> >Gentleman,
> >
> >A word of caution with the new Mitsubishi power bricks. Please be sure
> >to lap the bottom side of the brick flat using a belt sander with 150
> >grit and followed with 400 grit sand paper to achieve optimum
> >smoothness.
> >
> >No one is sure what they were thinking with the bottom side of the
> >module on the latest generation of bricks, but unless the heat sink
> >contact is in the 100% range, you risk blowing up the module due to a
> >ground and a heat resistance problem.
> >
>
>
> Ron Wright, N9EE
> 727-376-6575
> MICRO COMPUTER CONCEPTS
> Owner 146.64 repeater Tampa Bay, FL
> No tone, all are welcome.
>
>
>
>
>
>
>
> Yahoo! Groups Links
>
>
>
>

Re: Re: [Repeater-Builder] Re: 224 MHz PA fun and war stories

[Ron Wright]

To achieve a good heat sink coupling/bonding of 2 surfaces this is what heat 
sink compound is for.  Just having a smooth surface does not insure a good bond 
between 2 surfaces due to different flatness/shape.

I wonder in any Mitsubishi power bricks mounting instructions what they 
recommend.  Is its surface being used for any RF connection.  I hope not, not 
good engineering.

73, ron, n9ee/r




>From: DCFluX <[EMAIL PROTECTED]>
>Date: 2007/07/16 Mon AM 12:12:13 CDT
>To: Repeater-Builder@yahoogroups.com
>Subject: Re: [Repeater-Builder] Re: 224 MHz PA fun and war stories

>  
>Gentleman,
>
>A word of caution with the new Mitsubishi power bricks. Please be sure
>to lap the bottom side of the brick flat using a belt sander with 150
>grit and followed with 400 grit sand paper to achieve optimum
>smoothness.
>
>No one is sure what they were thinking with the bottom side of the
>module on the latest generation of bricks, but unless the heat sink
>contact is in the 100% range, you risk blowing up the module due to a
>ground and a heat resistance problem.
>


Ron Wright, N9EE
727-376-6575
MICRO COMPUTER CONCEPTS
Owner 146.64 repeater Tampa Bay, FL
No tone, all are welcome.

Re: [Repeater-Builder] Re: 224 MHz PA fun and war stories

[DCFluX]

Gentleman,

A word of caution with the new Mitsubishi power bricks. Please be sure
to lap the bottom side of the brick flat using a belt sander with 150
grit and followed with 400 grit sand paper to achieve optimum
smoothness.

No one is sure what they were thinking with the bottom side of the
module on the latest generation of bricks, but unless the heat sink
contact is in the 100% range, you risk blowing up the module due to a
ground and a heat resistance problem.

Re: [Repeater-Builder] Re: 224 MHz PA fun and war stories

[WD7F - John in Tucson]

Haven't tried it without a fan.  I would guess that the giant heat sink on
the original PA would probably handle the heat easily.  My only concern
would be the small contact area from each module; Would the heat dissipate
properly?  I have a PhD physicist business partner who could figure it out,
but it's about as easy to add the fan.

As K7IOU pointed out in the PA site, the fine print on that particular RF
module says that the unit was not appropriate for repeater use due to the
duty cycle.  Not sure why they came to that conclusion.  Of course, he read
that AFTER the modules had been purchased.  So, we went with them anyway.
Almost two years later... go figure.

de WD7F
John in Tucson

- Original Message - 
From: "Nate Duehr" <[EMAIL PROTECTED]>
To: 
Sent: Saturday, July 14, 2007 6:41 PM
Subject: Re: [Repeater-Builder] Re: 224 MHz PA fun and war stories

If a PA can't handle 48 hours of continuous key-down as-installed
(fans if one must, etc.), it shouldn't be used on a repeater.

> You can find it on K7IOU's micor conversion page at
> http://home.comcast.net/~micorrepeater/220mhzpa.htm

Thanks for sharing, John.  It's on the "must read" pile!  (GRIN)

--
Nate Duehr, WY0X
[EMAIL PROTECTED]







 
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Re: [Repeater-Builder] Re: 224 MHz PA fun and war stories

[Nate Duehr]

On Jul 14, 2007, at 7:57 AM, WD7F - John in Tucson wrote:


> Turned into a real challenge.  Using an RF splitter to divide the  
> input and
> a phased power combiner/bridge to sum the outputs, we manged to get  
> a very
> stable and bullet proof PA that once transmitted all night due to a
> controller malfunction.   The heavy duty heat sink and a fan  
> allowed the
> brick on the key operation with no problems.

If a PA can't handle 48 hours of continuous key-down as-installed  
(fans if one must, etc.), it shouldn't be used on a repeater.

> You can find it on K7IOU's micor conversion page at
> http://home.comcast.net/~micorrepeater/220mhzpa.htm

Thanks for sharing, John.  It's on the "must read" pile!  (GRIN)

--
Nate Duehr, WY0X
[EMAIL PROTECTED]

Re: [Repeater-Builder] Re: 224 MHz PA fun and war stories

[WD7F - John in Tucson]

We built a PA for the high band VHF Micor using two Mitsubishi modules.  We
had some problems getting sufficient drive out of our exciter conversion and
we wanted higher power, so we used two modules requiring 50 mW input for 35W
out.

Turned into a real challenge.  Using an RF splitter to divide the input and
a phased power combiner/bridge to sum the outputs, we manged to get a very
stable and bullet proof PA that once transmitted all night due to a
controller malfunction.   The heavy duty heat sink and a fan allowed the
brick on the key operation with no problems.

You can find it on K7IOU's micor conversion page at
http://home.comcast.net/~micorrepeater/220mhzpa.htm

de WD7F
John in Tucson





 
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Re: [Repeater-Builder] Re: 224 MHz PA fun and war stories

[Mike Morris]

The Condor conversions for the GEs are on the GE page at repeater-builder.

Their web site is at 

Mike WA6ILQ


At 12:07 AM 07/14/07, you wrote:
>Same thing with the Micor 223/224 MHz conversions. We simply
>used bricks with trailing low pass filters.  I'm checking to
>see what type of docs I have around for the pa sections.
>
>There's a really well done/built linked 223/224 linked system on the
>west coast called the Condor System. You might search the web
>for the conversion information related to that equipment. I based
>one of my last brick projects on that same circuit...  the hard part
>is trying to find all the proper parts (caps rated for vhf with
>a decent D-factor) at decent prices.
>
>A few years back there were a modest amount of small size Milcom
>220 Mhz hybrid pa's on ebay. Another source of 35 watts on 224 MHz
>if you can find them still.
>
>s.
>
> > Nate Duehr <[EMAIL PROTECTED]> wrote:
> > Everything I've read about converting MASTR II PA's from VHF
> > to 220 doesn't look too good.
> >
> > I have heard rumor that moving a MASTR III PA might be easier.
> > No desire to hunt for one and try it, though.
> >
> > Most of the MASTR II 220 conversions I've seen on-air took a
> > "brick module" 220 PA from RF Parts and fed that from the
> > converted M2 exciter, for around 25-35W out.
> >
> > Nate Duehr
> > [EMAIL PROTECTED]
> >
>
>
>
>
>
>
>Yahoo! Groups Links
>
>
>

[Repeater-Builder] Re: 224 MHz PA fun and war stories

[skipp025]

Same thing with the Micor 223/224 MHz conversions. We simply 
used bricks with trailing low pass filters.  I'm checking to 
see what type of docs I have around for the pa sections.  

There's a really well done/built linked 223/224 linked system on the 
west coast called the Condor System. You might search the web 
for the conversion information related to that equipment. I based 
one of my last brick projects on that same circuit...  the hard part 
is trying to find all the proper parts (caps rated for vhf with 
a decent D-factor) at decent prices. 

A few years back there were a modest amount of small size Milcom 
220 Mhz hybrid pa's on ebay. Another source of 35 watts on 224 MHz 
if you can find them still. 

s. 

> Nate Duehr <[EMAIL PROTECTED]> wrote:
> Everything I've read about converting MASTR II PA's from VHF 
> to 220 doesn't look too good.
> 
> I have heard rumor that moving a MASTR III PA might be easier.  
> No desire to hunt for one and try it, though.
> 
> Most of the MASTR II 220 conversions I've seen on-air took a 
> "brick module" 220 PA from RF Parts and fed that from the 
> converted M2 exciter, for around 25-35W out.
> 
> Nate Duehr
> [EMAIL PROTECTED]
>