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Re: [Amps] Question about SPE 1.3K-FA amplifier

Subject: Re: [Amps] Question about SPE 1.3K-FA amplifier
From: Manfred Mornhinweg <>
Date: Thu, 12 Nov 2015 14:02:16 +0000
List-post: <">>
Here is a link to what looks like the Test Report for
FCC Type Acceptance.

Curious as to what folks think about the results.

It seems to be a test report made _by_ an SPE guy _for_ FCC. So it's not an independent test. I would love to see an independent test report, and specially a more complete one, showing IMD at different power levels up to the full rating.

Their test method seems a bit flawed imo.  You can't test
any linear amp, by stuffing a 2 tone signal into the mic jack.
Unless the xcvr is running in class A.  In this case, the icom 7800
used for the test, afaik, does not run class A.

Jim, this is not as bad as you think. True, when you run a typical radio at full power, its own IMD is too bad to allow accurately measuring the IMD of a good amp. But note in the test report that the harmonics tests were done at around 44W drive for 1300W out, so the IMD tests with 1000W PEP out must have been done with roughly 30-35W PEP drive. At that power level most radios are very much cleaner than at full power! I have never measured the IMD performance of the 7800, but the radios I own typically measure a 3rd IMD about -28dB at 100W, and as good as -40dB or better at 30W. So, if the 7800 behaves like the Kenwood radios I have, it's indeed OK to test that amplifier with a simple radio and two-tone generator.

That wouldn't be good enough to test an ultra-clean amplifier, of course, but neither this one nor most other ham amps are ultra clean!

Of course, testing a 1300W rated amp at 1000W, raises the suspicion that this is the highest power at which it can produce an IMD performance that the FCC would approve!

##  If SPE cant / doesn't want to provide a schematic for this amp,
or any of their other amps, I would not touch it, or buy one.

I like that attitude. Although in the case of amplifiers the circuit is simple enough that one can mostly repair them without a schematic, but still I think it's against ham tradition and interests to buy "black boxes" with secret "don't touch" contents.

##  They need to re-run the test, this time using TWO xcvrs, each feeding a
cxr into a hybrid etc, then into the input of the amp.....and do it with
the amp running 1.3 kw pep out.

They don't need two transceivers. At full power, with 45W drive, most transceivers are good enough for testing, specially considering that the IMD of this amp will probably be rather poor. If the amp produces a 3rd IMD of -20dB or so, and the transceiver at 45W PEP produces -35dB, that's enough difference to obtain a pretty accurate measurement result for the amp's IMD.

I wonder what will happen when some hams, in the heat of contesting or whatever, drive this amp with the full 100W of their radios, and of course without bothering to wire up the ALC. Will the 35,000 lines of code shut down the amplifier, or will it happily produce 1300-1500W of saturated output power, with -10dB IMD?

Of course, some hams do the exact same thing with tube amps that require less than 100W drive!

The SPE 1.3K-FA comes with a 2 Year Warranty.
Warranty work (for the most part) is done here in
the States.

With that kind of Warranty SPE must be very
confident in the Amps survival.

Dick, I noticed the same thing. I'm pretty sure that they run the FET pretty hard into saturation, so that the dissipation is relatively low at full output. That, along with effective SWR protection, should make the FET survive.

And I would love to know whether they just use plain simple class AB and allow the IMD to shoot through the roof at 1300-1500W saturated output, or if they use a clever biasing scheme that keeps the IMD somewhat under control even when the FET is driven into saturation.

Mine should be here this week !!

Great! So we will get first-hand reports!

If you ever dare taking the cover off, I would be interested in a clear photo of the bias circuitry, just to spy out whether or not they are modulating the bias.

Let us know your impressions!


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