Duplicating the KPA100 LP filters

[Vic K2VCO]

I have a very nice well-built Henry Radio 100B solid state amplifier.
Like the KPA100 it uses a pair of 2sc2879's to produce 100 watts.  It
has a heat sink and fan that looks like it would be enough for a KW!
Unfortunately, it doesn't have built in LP filters so it can't be used
to feed an antenna.

I'm thinking about duplicating the KPA100 LP filter section so I can use
this amp as an output stage for another rig.  This sounds like a
no-brainer, but I wonder if there's any reason not to do this?

Also, does anyone know the manufacturer and model number of the relays
(K3-K12) that Elecraft used?  I would have to take my KPA apart to look!
--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
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[Phil Kane-2]

On Sun, 18 Jun 2006 21:36:25 -0700, Vic K2VCO wrote:

>I'm thinking about duplicating the KPA100 LP filter section so I can use
>this amp as an output stage for another rig.  This sounds like a
>no-brainer, but I wonder if there's any reason not to do this?

  Why not use an outboard LP Filter like most of us have done
  for decades?  I wouldn't connect ANYTHING to a HF antenna
  without one.

--
   73 de K2ASP - Phil Kane
   Elecraft K2/100   5402



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[Vic K2VCO]

Phil Kane wrote:
> On Sun, 18 Jun 2006 21:36:25 -0700, Vic K2VCO wrote:
>
>> I'm thinking about duplicating the KPA100 LP filter section so I can use
>> this amp as an output stage for another rig.  

>   Why not use an outboard LP Filter like most of us have done
>   for decades?  I wouldn't connect ANYTHING to a HF antenna
>   without one.

Well, you need several selectable filters, because you need to reduce
the low-order harmonics.  The usual lowpass TVI filter cuts off around
30 MHz or even 50 MHz.  But you need to eliminate the 14 MHz (etc)
harmonic that goes with your 7 MHz desired signal.  A tube rig doesn't
have this problem because the tuned plate tank circuit has enough
selectivity to reduce these enough.
--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
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[Geoffrey Mackenzie-Kennedy-2]

Vicd Rosenthal wrote:

> I'm thinking about duplicating the KPA100 LP filter section so I can use
> this amp as an output stage for another rig.  This sounds like a
> no-brainer, but I wonder if there's any reason not to do this?
>
> Also, does anyone know the manufacturer and model number of the relays
> (K3-K12) that Elecraft used?  I would have to take my KPA apart to look!

-----------------------------------------------------------------------

Hi Vic,

My KPA100 purchased in early 2003 uses OMRON type G6E - 134P - ST -US relays
for K3 - K12 (and K1, K2).  Unless I'm mistaken the contact rating is 0.4A @
125VAC  or  2.0A @ 30VDC which seems to be a bit 'light', but no problems so
far.

My KAT100, same vintage, uses HASCD  KL1TC 12DC12 relays for K1 - K18,
contacts rated at 12A @ 28VDC. This rating is typical for use at 100W HF RF
with a good safety margin.

I would strongly recommend that you include a lowpass filter between the
KPA100 filters and your antenna tuner (or antenna if no tuner is used),
whose cutoff is around 32 MHz.  HF  LP Filters including  the type used in
the KPA100, especially when densely packaged, can exhibit 'peaks' of low
attenuation at VHF and UHF upwards. Toroidal coils do talk to one another to
some degree.

73,
Geoff
GM4ESD



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