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Reviews Categories | Amplifiers: RF Power - HF & HF+6M | Ramsey Qamp 40 Help


Reviews Summary for Ramsey Qamp 40
Ramsey Qamp 40 Reviews: 13 Average rating: 3.5/5 MSRP: $$49.95
Description: 40 meter linear amp
Product is in production.
More info: http://www.ramseyelectronics.com/cgi-bin/commerce.exe?preadd=action&key=QAMP
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IZ4KBS Rating: 3/5 Jun 5, 2010 11:04 Send this review to a friend
don't think it will ever work out of the box  Time owned: 0 to 3 months
In spite of the many negative reviews I bought two of them, to make it worth the shipping from the US into Europe. So far I have only built the 40m unit, while the 20m one is still sitting in its package unbuilt. First of all, I did beforehand many of the mods suggested by others, namely:

* 10 ohm 1/2 watt resistors in series with the MOSFETs' gates.

* 100 ohm 2 watts resistor in parallel with the primary of T2, to make the rig see an acceptable VSWR level. Without this, the input VSWR was sky high.

* replaced D2 with a germanium diode 1N34A, and increased C10 to 470nF to prevent the RX/TX relay from chattering.

* added additional, larger heathsinks, and improved the thermal conductivity with some silicon grease.

While winding L2 I pressed too hard and I broke the T44-6 toroid core. Thanks to the invaluable "mini Ring Core Calculator" program, I was able to make a replacement L2 using a T50-2 core.

For those who don't know, the ferrite binocular cores of T1 and T2 are conductive! (their resistance is in the order of a few hundred ohms). When threading the supplied enameled wire through them, the chances that the bare wire gets exposed and touches the core, and possible in multiple places, are *very* high. Although I'm not a "first time coil winder", out of four attempts I got a short between the primary and the secondary windings 3 times! So I junked the enameled wire and used PVC insulated #26 AWG wire instead, and I recommend you do the same.

The I moved on to testing the unit, with the top cover removed, and it was pumping out about 12-13 watts at 12Vdc of power supply. After only a few minutes of keying with my NorCal 40A set at 1.8 watts, temperature on the heathsinks had increased to about 95-105 C, so the heathsinks were *very* hot and could not be touched, but I didn't worry too much. I should have! After half an hour of testing, and in spite of the many preventive mods listed above, one of the MOSFETs shorted and went up in smoke, taking a couple of PCB traces with it because the original design has no fuses, and my DC power supply can deliver more than 30 amps before its short-circuit protection trips. I promptly cut the power, then replaced the two MOSFETs with a couple of cheap IRF-510, reworked the vaporized PCB traces, and added a 5A fuse in place of jumper JMP1. Then, because of the different MOSFETs, I also had to lower R2 to 2.2 Kohm to get the correct bias. Lastly, I added a 12V CPU cooling fan on top of the MOSFETs and provided pleny of ventilation by modifying the supplied plastic case a bit. The second test went fine, with the two MOSFEts that now get just about warm, also with the top cover applied, and after several QSOs the unit seems to work OK now.

In conclusion, not only this thing will most likely not work out of the box, but it may fail even if you do the suggeted mods, unless you also replace the stock MOSFETs and apply a cooling fan. The final result can be seen at this link: http://www.strozzi.it/users/carlo/hamradio/qamp-40/ .

In spite of all the troubles, and of the fact that as supplied the unit would deserve a rating of 0/5, with a bit of skillful patience it can be turned into something really useful, which I think has no competitors in its price range (including the cost of the mods). So in the end I'm giving it 3/5, because now it makes for an excellent QRP accessory, for those days where conditions are marginal and a bit of QRO can make the difference.

Another two mods that I did, which I think are quite important and that I forgot to list in my previous review, are: * used 1/2 watt resistors for R8 and R9. * replaced C4, C5, C6 and C7 with 500V mica capacitors.
 
WD6DBM Rating: 1/5 Nov 28, 2008 16:56 Send this review to a friend
Junk  Time owned: 0 to 3 months
4 seconds after power up I got heavy smoke, then a cap exploded before I could pull the power. I checked my wiring and it was all correct. I can't get proper bias on the power transistors, and with the very inadequate instructions I'm not sure if I will waste more time on this project.

I have built many Heathkits, a KX1, RockMites, etc. The quality of the kit is poor.

I'll make a call to Ramsey to see if I can get help, but based on the other reviews I am not holding out hope.

The parts are pretty cheap
 
KSAVES2 Rating: 3/5 Feb 4, 2006 17:14 Send this review to a friend
QRP amplifier  Time owned: 0 to 3 months
Am not a licensed ham yet but have been building some simple QRP radios for CW use. I have a 5 watt and 100 watt
dummy loads I use for bench work. Having built an SMT
Magnetic Anomaly Detection device for model rockets
(http://www.aeroconsystems.com/electronics/mad.htm)
I felt I had the skills to tackle a simple amplifier. And yes I am studying the ARRL manuals, learning code and I don't believe in unlicensed use of the airwaves.

I researched the net for some low powered QRP amps and found some plans but decided to order the Qamp 40 from Ramsey Electronics. I built a simple Tixie from a bare board from Far Circuits and I probably spent close to the cost of the QRP 40 acquiring the parts for it. Suffice it to say, I didn't want to have to track down parts for an amplifier project. Being new, I don't have a junk parts pile
yet! I also didn't read the prior review of the Qamp 20 here
before I ordered my unit. Most reviewers gave the Qamp 20 a poor quality review. They mentioned that the pc board was very inferior. The board I received with the Qamp 40 was of fine quality and soldered well. None of the pads lifted up.

The unit arrived adequately packed and the instructions were relatively clear. I was able to solder all the parts to the board except the three toroids and two large tapped ferrite beads in one evening. When I got to winding the toroids and beads, I found out I was short on the #24 enameled wire. Emailed Ramsey and I got replies within 24 hours. This was better than what others experienced with the Qamp 20 reviews. They sent me the needed wire and I was able to get the winding done and the parts soldered to the board.

Now it was time to set the thing up. I was very fearful here in that I saw some reviews that the Qamp 20 "just burned up" on powerup. I emailed Ramsey some questions about the alignment procedure and again they answered them within 24 hours. Only a DVM is needed to set the unit up. The positive probe goes to a test point on the board and the negative to ground. A jumper to the collector on Q3, 2N3904 transistor, needs to go to ground. Had to look up on the internet where the collector was on the TO-92 case. A bias pot is turned to the minimum setting to start.
The instructions talk about measuring the current draw but I was emailed back that one doesn't have to worry about this.
I was advised that one just has to make sure the voltage is between 3.2 and 3.5V. I adjusted the range of the pot to see if it changed the voltage at the test point. (It did) I then set the pot so it read 3.4 volts or thereabouts.
I connected up the Tixie which actually is running at 200 to 300mW output. The instructions say to use a transmitter 1/2 to two watts. I did it anyways. The relay froze close on the Qamp 40 and I cut the power. Hmmm, maybe too little driving power? I'll try my Peanut Whistle from
http://www.hamradiofun.com/peanut-whistle.htm.
Sure enough, the Qamp 40 worked. I had the setup running into a cheap Workman SWR-3P and my Oak Hills Research
100 watt dummy load. I then carefully turned down the bias
and the power output dropped through the meter. Again, I remembered the upper limit of the pot that gave a voltage of an acceptable level and connected up the Tixie and keyed it while adjusting the bias. That made the difference.
The relay no longer froze and the keyer was working fine.
I was getting a couple of watts with the Tixie into the dummy as opposed to roughly ten watts with the Peanut Whistle. Now my readings are relative as I have no doubt that my meter is likely inaccurate. I believe it was only adequate enough to show there was some amplification of
the input rf power. Also was monitoring the signal with
a Grundig S350 SW unit. Doubt if any rf got outside my basement!

I won't be able to review onair performance and that is why I rated the item as OK. The prior reviews of the Qamp20 commented upon "the poor quality parts" and "poor tech support". I didn't have those problems. There were the issues with the wire but they quickly fixed it.

It looks like the alignment procedure may need to be repeated when using a different transmitter/transceiver.
It would be easy enough to install a shorting switch from the collector of Q3 to ground and a jack to connect to a DVM from the test point. Only problem is that the bias pot sits in front of a mounting screw in the Ramsey case so one can't simply drill a hole for access. If I like the unit after I'm licensed and onair, I'll mount it in a different case with those changes. Disclaimer: I am in no way connected to the Ramsey company. I became interested in Ham Radio as I wanted to build homemade tracking transmitters into high powered model rockets. Want to be licensed so I can transmit my call with a K1EL keyer on 2 meters from 5,000 feet up! Then go track the downed model with a handheld
and Yagi.
Kurt Savegnago
ksaves2@sbcglobal.net
 
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