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Re: [Amps] RF2K+ LDMOS linear

Subject: Re: [Amps] RF2K+ LDMOS linear
From: M Gerber <>
Date: Sun, 4 Jun 2017 10:02:53 -1000
List-post: <>
Having built a W6PQL two pallet (2XBLF188XR), I do have some concerns
regarding the RF-KIT amp.

I have an older (1 yr ago) kit and I flow soldered each of the BLF188's to
individual 3" X 5.5" X 0.5" copper spreaders ordered from W6PQL. The two
spreaders are then mounted to a 10" X 10" X 3.5" aluminum heat sink with
(3) 80mm 38 CFM fans. W6PQL's controller board turns on the fans during
transmit and the fans are on full-time once the temperature reaches a
specified level. The fans are noisy, but I wear headphones, so that is not
a major issue for me.

I am a contester and have challenged my amp under these conditions. I do
not have air conditioning at my QTH and I cannot operate a RTTY contest at
full power with this amp due to thermal issues. Additionally, the heat
sink/spreader get quite hot to the touch but never so bad that I cannot
keep a finger on the sink or spreader. During contesting, I partially lift
the cover to allow for better ventilation. I have had the amp shut rarely
down due to overtemp on CW.

The RF-KIT amp appears to have both BLF188's on a single smaller spreader
and heatsink. Hard to say what the fan complement is here. I would think
this to be a concern particularly if you are looking to contest with this

While it is interesting that flow soldering the LDMOS to the copper
spreader (requires temps to 400F (200C)) does not appear to does not appear
to directly damage the BLF188, there is no question that heat will takes it
toll on the BLF188 or any other LDMOS. I am still hoping someone will
design a nice water-cooled SSPA but I do understand it may be overkill.
Regardless of tube or transistor, at the efficiencies we see in amplifier
design there is likely more 500W to waste. Try putting your hand over the
chimney vent of tube amp during the heat of battle---it can be as
uncomfortable as running your hand in front of a hair dryer or heat gun.

I personally would like to see a combination of the Flex Power Genius and
Elecraft's KPA1500 based on what I have read as I have not seen either one
in person. I am a CW operator and QSK is way cool. I would love to have an
amplifier that I felt good about challenging the relays or PIN diodes such
that QSK would be a "safe" way to operate. I have an Alpha 9500 and 8410,
both of which are collecting dust, and even with the vacuum relays in them,
the noise and concern for relay damage never gave me the confidence to
operate QSK with either of these amps. I have heard the ACOM 2000 operate
QSK, and it is very quiet. While I do realize that the vacuum relays
probably are up to prolonged QSK and that my concern may be more "noise"
related, the KPA1500 is to have PIN diodes. This means silent T/R.

I do not know what filtering configuration is in the KPA1500, but the Flex
has diplexed filters. From what I know of LDMOS amps, the IMD products on
some bands can be down as little as 10dB. That means in excess of 150W (10%
of 1500) needs to be dissipated/absorbed in the filter-- even more because
the other IMD products are also being reflected. The diplexer design, at
least at this point in time, short of using an ANAN SDR with Pure Signal,
seems to be a very solid choice over a conventional multipole LC LP-filter.
Yes, the diplexer design is more expensive, but a better choice from an
engineering point of view. It is noteworthy that the KPA1500 has a TX
SAMPLE BNC input for closed-loop pre-distortion such as Pure Signal. I
think it is safe to say the majority of contesters are not using ANAN SDR's
but my suspicion is that Elecraft is hard at work on an SDR with some type
of closed-loop pre-distortion to compete with Flex, ANAN and Icom,
especially if Rob Sherwood is correct about the number of Icom 7300's that
have been sold.

Lastly, there has been lots of discussion regarding transmit spectral
purity, IMD. etc. I believe these efforts are worthwhile. However, whether
it is contesting and trying to create elbow room on your run frequency or
trying to break a pile-up to P5 or 3Y0, hams are going to turn up the gain,
power, speech processor, etc trying to eek out that seemingly meaningful
last little competitive advantage which will almost certainly partially
undo the progress made on this front---and I sincerely doubt this behavior
will ever change.

These are interesting times both with SDR and LDMOS. I am sure we will
continue to see exciting new gear despite the demise of Cycle 24 .

73--Mark WH7W

 I'm with Steve here. The old saw of "build a better mouse trap and
the world will beat a path to your door" is almost always false because
it's hard to believe the hype surrounding stuff. If an amp maker wants to
crank up the sales in the US of their amps, by far the best way would be to
put it in the hands of someone who has a good tech reputation in the
community, can give it a serious contest workout and who also has the
ability to do a basicIMD test.

There are many folks of that description. Before I shovel what is going
to be nearly 8K into a box, I really would feel a lot better if I heard
that they lived through a couple of contests over at W3LPL, etc and Frank
saidthey hummed along fine. I'm using LPL as an example here. My point
is advertising and social media and endorsements from guys in EU are a lot
less meaningful than a country local here in the US.

Made the exact same argument to a Chinese maker when he was trying to
get going but he unfortunately just could not wrap their head around
the marketing aspect of a product roll out. The ham universe is pretty
small - and an endorsement by someone objective and authoritative carries
far more weight in this market than in others, especially given the huge
financial investment something like this involves.


-----Original Message----- From: Jim Thomson

Sent: Sunday, June 04, 2017 11:48 AMTo: amps@contesting.comSubject:
[Amps] RF2K+ LDMOS linear
Date: Sun, 04 Jun 2017 07:58:54 -0600From: Steve London
<>To: amps@contesting.comSubject: Re: [Amps] RF2K+
LDMOS linear
<I would not declare tube amplifiers dead until a legal limit,
SSamplifier repeatedly proves itself in serious contest conditions.
I'mnot talking about the guy who casually makes 500
search-and-pounceQSO's. I'm talking about the balls-to-the-walls,
SO2R, all-band guy/galwho operates close to 48 hours, running stations
the entire time.Mistakes happen under these conditions - ooops, forgot
to change thetornado tuner on the 80 when moving from 3700 to 3800,
etc. Or, RF fromone amp gets into the other amp and fools it's
The only production SS amp that has come close to proving itself
underthere conditions is the SPE line. Even they aren't perfect.
See . That
was anSPE 2K. In all fairness to SPE,
see . A pair
ofSPE 1.3K's that worked flawlessly. (However, not at the legal
I would love to borrow a pair of these RF-Kit amps and put them
toserious use in one of my SO2R contest efforts.
73,Steve, N2IC
##  High swr, so what, amp kicks offline at some pre-set
threshold.They are already in use across rtty contests.
Fans  arepwm controlled, so heat is not an issue.   Eff is high at
65-70%.IMD is typ –40db pep..using the newer german made LP
filters.Mark tells me these amps are 100% duty cycle rated, all
modes.If they survive a rtty contest, ssb + cw should be a lollygog.
## You are right though...  send some off to contest sites..and really beat

on em for the weekend. Tube amps days are numbered, the writing is on
the wall.

Jim   VE7RF
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