Luckily - most of the world is not the US and gains of over 15dB are legal
and common in non-us amplifiers. Modern FETs have much more gain than older
devices and it would be quite normal to have 20dB gain from a stage - even
after some feedback. There is an interesting design in the latest Dubus
Sorry, I should have said, ...uses an input attenuator of more than a few dB.
They help with impedance matching and stabilization, so you probably couldn't
take them out anyway. In any case, it would only reduce drive requirement to
maybe 30 W.
73,
Scott K9MA
On Dec 20, 2010, at 7:28 PM,
The Ameritron ALS-600 has about a 15 ohm input impedance. Then they put a
series 35 ohm resistor for matching and reducing gain.
This is exactly right. The MRF150 MOSFETs used in ALS600 are rated at 20dB. I
know people who homebrewed similar amplifier without series resistor and have
full
Of course, 20 dB of gain is not legal in the US, at least for commercial
amplifiers, so it makes sense that Ameritron would use an attenuator, as it
also saves them the cost of a matching transformer.
Scott K9MA
On Dec 21, 2010, at 12:08 PM, k.i...@comcast.net wrote:
This is exactly
Almost 30 years ago now, before I was 99.% a QRPer, I had an Alpha
76CA (3 tubes). It had a giant swamping pad on the input (I still
have it - the swamping pad, that is). Just take it out and like
magic, you could drive the amp with QRP. My intention was never to
exceed legal limit, just to
It's very unlikely any solid-state amplifier uses an input attenuator:
Transistors and FET's just don't have that much gain.
Grid-driven tube amplifiers may indeed have enough gain (without the input
pad), but there are a couple potential problems. Without the input pad, the
amplifier may
Well... keep in mind that an input attenuator also reduces the SWR seen by the
exciter.
Even a relatively small 3 dB pad means that the SWR can't go above 3:1 even if
the input
impedance of the amplifier was zero or infinite!
On 12/20/2010 2:09 PM, DOUGLAS ZWIEBEL wrote:
Almost 30 years ago
On 12/20/2010 2:09 PM, DOUGLAS ZWIEBEL wrote:
Almost 30 years ago now, before I was 99.% a QRPer, I had an Alpha
76CA (3 tubes). It had a giant swamping pad on the input (I still
have it - the swamping pad, that is). Just take it out and like
magic, you could drive the amp with QRP.
Fred and all,
That is something to be heeded. The Elecraft example is that the K2
key-clicks were not a problem until the KPA100 was introduced. The
added gain of the KPA100 caused that problem to be amplified (along with
the signal). Elecraft responded with the Keying Waveshape Mod kit
It's very unlikely any solid-state amplifier uses an input attenuator:
Transistors and FET's just don't have that much gain.
The Ameritron ALS-600 has about a 15 ohm input impedance. Then they put a
series 35 ohm resistor for matching and reducing gain.
Phil - AD5X
Phil,
Your statement amplifies the difference between ham assumptions and
reality.
The data-sheet indications of gain do not consider the input impedance
(and loading of the driver), that parameter is quite important in actual
use -- if the amplifier does not provide a good load to the
On 12/20/2010 4:57 PM, Fred Jensen wrote:
The [in]famous BW all band folded dipole capitalized on this -- big
50 ohm load resistor = 50 ohms everywhere. I still see them around
National Guard Armories.
You can see one in my back yard as well, 30 ft AGL. It's the
best that I can do for
...@mailman.qth.net] On Behalf Of Phil Kane
Sent: Monday, December 20, 2010 7:16 PM
To: elecraft@mailman.qth.net
Subject: Re: [Elecraft] OT: modifying your amp for lower drive requirement
On 12/20/2010 4:57 PM, Fred Jensen wrote:
The [in]famous BW all band folded dipole capitalized on this -- big
50 ohm
On 12/20/2010 5:28 PM, Phil Debbie Salas wrote:
It's very unlikely any solid-state amplifier uses an input attenuator:
Transistors and FET's just don't have that much gain.
The Ameritron ALS-600 has about a 15 ohm input impedance. Then they put a
series 35 ohm resistor for matching and
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