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Author Topic: Anyone Build the EB63 HF Amp from CCI?  (Read 3079 times)
KG7RS
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Posts: 15




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« on: December 06, 2000, 09:16:59 AM »

Hi all,
I'm looking to exchange experiences with building any of the solid-state HF linear amplifiers offered by Communications Concepts, CCI. They offer circuit boards and component kits for many of the amplifiers described in older Motorola engineering bulletins. I recently built the EB63 140-w amp, which uses a PP pair of MRF-454's. The amp does a great job for me when driven with my Elecraft K2 on those (rare!) occasions when QRP won't get the job done.
I'd specifically like some ideas on designs for bandswitching lowpass filters. Has anybody improved upon the existing bias regulation, TR switching etc? Any long-term reliability issues? Any/all comments would be appreciated.

72/73, John, KG7RS
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WB2WIK
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Posts: 20613




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« Reply #1 on: February 02, 2001, 06:21:52 PM »

It might be superfluous now, but obviously I have built the EB-63 and already commented on the results on this website at eham.net/reviews/detail/1223, as you have.

It is very easy to dramatically improve the RF-sensed T-R switching circuit.  I didn't use the Motorola circuit at all, instead used a 5082-2800 hot carrier diode detector (decoupled from the RF input line with a .001uF cap and 1K resistor or so) driving an MPS-A13 (I think it was) Darlington amplifier which pulls in a sensitive Radio Shack 12V relay "instantly" and reliably, with the decay time set by an adjustable R-C circuit in the charge line to the Darlington.  This whole circuit is about half the size of a postage stamp, built on a tiny piece of perfboard supported by the relay itself, and probably cost $2 to build.  Extremely reliable, no drop outs, no glitches, works fine on all bands, as it has for about 11 years since I installed it.

As stated in my review from early December, I never bothered with the bandpass filters at all, and frankly, I'm glad I didn't.  After writing the review on this site it raised my curiosity about spectral purity of this amp (which I can't recall ever checking initially), so I ran some tests.  With 5W drive and 100W (approx) output, the amp is still in its linear range and purity is excellent without filtering -- worst case was 2nd harmonic of 14 MHz, down about 42 dB at +50dBm Po (100W).  3rd harmonics are well below this, across the spectra.  My particular amp enters the non-linear region at about 120W out (7W drive) and is compressed 3dB at 150W out (10W drive).  The obvious degradation in purity is easily noted on the spectrum analyzer....at +52dBm Po, 2nd harmonic at 14 MHz is down only 29 dB, a 13 dB degradation.  But again, at this point, the amplifier is in compression, and something's got to give.

Signal source for this test was my TS850S/AT (adjustable Po down to <1W) run through DuneStar bandpass filters to the input of the EB-63; output of the EB-63 to 1.2kW Bird Termaline passive load, through -20dB HP 778D Dual Directional Coupler.  -20dB decoupled port on the coupler run through 20dB 50 Ohm inline attenuator (Narda) to HP 141T storage display w/110 MHz spectrum analyzer plug-in.  Purity test on source without amplifier indicated 2x down >65 dB, 3x down >75 dB at 5-10W drive levels.

Based on this, I'd recommend NO EXTERNAL FILTERING at all is necessary with the EB-63 provided you stay within its linear range, which appears to be ~100W Po @ 13.8Vdc supply voltage.

Have fun!

Steve WB2WIK

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