REVIEW OF RAMSEY QAMP LINEAR AMPLIFIERS
April 30th, 2008 by hamslife
Ramsey Electronics has several inexpensive easy to assemble electronic kits. Some are specifically amateur radio related and others are not. The QAMP40, QAMP30, and QAMP20 are 40,30 and 20 meter 20 watt linear amplifier. Being linear it will run CW, SSB, or AM. It can be driven with ½ to 2 watts with a power requirement of 12 VDC at 4 Amps.
The amplifiers have about a 10 DB gain so 1 watt in equals 10 watts out and 2 watts in equals 20 watts out. They were designed to be used with the Ramsey QRP transmitters which run at about 1 watt.
The instruction booklet, as with all their kits I have assembled so far, is very well done and can be followed by anyone even with no electronic knowledge.
Ramsey’s estimated assembly time is 4 hours for beginner, 2 hours for intermediate, and 1.5 hours for advanced builders. I did not time myself but I would say that their timing estimate is fairly accurate.
The instruction booklet, as with all their kits I have assembled so far, is very well done and can be followed by anyone even with no electronic knowledge.
Alignment is very easy. Basically it is just a matter of setting the bias by adjusting a small potentiometer.
The work horses of the amplifier are two P16NF06 MOSFET transistors. They are run in Push-Pull format so as to reduce potential second harmonic output. It has a 3 stage pi network low pass filter output to further reduce the harmonic output. The input and output to the transistor are both through ferrite wideband transformers.
transformers.
The exciter input uses a T-R relay circuit which is operated by a simple diode detector to sense when RF is applied and a two transistors amplifier circuit to drive the relay. If the power switch is not on the relay will not actuate and thus the exciter can be run “bare foot” but when the power is on it will switch on as soon as the exciter is keyed.
When testing the QAMP I found that ½ watts in gave 5 watts out and 1 watt in gave 10 watts output. An IFR service monitor’s power meter was used for the test. The efficiency is about 30 to 35% which is about where a class AB amplifier should run.
The kits require winding three toroid coils and two ferrite bead transformers. They use enamel insulated wire which Ramsey says can be tined to prepare for soldering without removing the insulation. About a year ago I purchased some of these kits and they surprised me because I was able to tin them using Ramsey’s process but recently I purchased a few more and found the insulation would not burn off. Thus scraping off insulation before soldering was necessary before I was able to solder them. I suspect they may have changed supplier of this wire.
Another problem I have is they supply the MOSFET transistors in plastic envelopes that do not appear to be ESD (Electrostatic Discharge) protection packages. They also do not recommend ESD caution be taken during construction which makes me wonder how many of these transistors are destroyed by electrostatic discharge by builders who are not aware of the danger.
Over all, considering the cost, they are very great little amplifiers to boost the power of your QRP rig.
This entry was posted on Wednesday, April 30th, 2008 at 8:47 pm and is filed under Kit, Amplifiers, Linear Amplifier, Class AB amplifier, Ampliduce Modulation, Single Sideband, amateur radio, CW, SSB, ham radio. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
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