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Reviews Categories | Amplifiers: RF Power - HF & HF+6M | Ramsey Electronics QAMP-20 Linear Amp Help


Reviews Summary for Ramsey Electronics QAMP-20 Linear Amp
Ramsey Electronics QAMP-20 Linear Amp Reviews: 19 Average rating: 1.9/5 MSRP: $49.95
Description: 20W Linear Amp to give a modest QRO boost to QRP SSB/CW rigs. Available for 80/40/30/20M. Enclosure also available.
Product is in production.
More info: http://www.ramseyelectronics.com
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W7MBR Rating: 0/5 Jul 5, 2014 22:42 Send this review to a friend
AWFUL "0"  Time owned: 0 to 3 months
I didn't think Ramsey could do it but this is their worst effort so far. I've put countless Heathkits and others together since 1960 so I would consider myself an advanced kit builder. After completing the Ramsey 20 meter amplifier kit it smoked and blew traces on the pc board due to a shorted (out of the box) mosfet power transistor. No fuse to protect anything! I purchased 2 new Radio Shack IRF510's mosfets and did some mods but the power out is below Ramsey's advertised claims. 1 watt in and I get about 7 watts out. Teaming it together with their QRP teansmitter and receiver you couldn't find anything worse. The receiver drifts so badly I could hardly believe it. I guarantee you will not be happy with this amplifier. If I were a Ramsey engineer I would be ashamed of myself!
 
EA2IO Rating: 3/5 May 18, 2013 03:23 Send this review to a friend
My QAMP20 works  Time owned: 0 to 3 months
When I started building the QAMP20 knew the problems the kit but I had the advantage of knowing how other radio friends they had been resolved.
I have done the following:
--Replace capacitor C10 by other 470 nF.
-- Replace C4 and C7 by 180 pF. but 500 V.
-- Replace C5 and C6 by 330 pF. but 500 V.
--Replace R8 and R9 by 270 ohm but 1 W.
-- I placed a 10 ohm ½ W. resistor in serie with Gates MOSFET.
-- I put 1 red LED on the front panel.
-- A 5A fuse instead of JMP 1.
-- A two-inch fan inside the box and over the heatsinks
-- Two new larger heatsinks below the originals.
-- I replaced the back panel by another one in aluminum, in order to place two connectors input / output SO239.

You can see a few pictures at the following link:
https://plus.google.com/photos/117869596909184379910/albums/5879020281538066065
The BIAS is set to 210 mA and the voltage at TP1 is 2.4 V.
I can get between 15 and 18 watts and the MOSFETs are always cold.
The relay is always quiet and not annoying.
73 ! and good DX.
 
W5GNB Rating: 1/5 Jan 3, 2013 18:25 Send this review to a friend
REAL JUNK !!  Time owned: 6 to 12 months
The kit is Poorly documented. Parts are CHEAP! After assembly, SMOKE quickly appeared just before the Finals EXPLODED !
I had to do several Mods before the thing would work. Changed the finals to IRF530 Mosfets, added 10-ohn resistors to the gates, added a 5-amp fuse. Added a 47-uf cap to the RF keying circuit so that the T/R Relay would not key as fast as your keyer.. Wow !!
NOW it works fine but it should have been this way out of the box.... RAMSEY should team up with MFJ, then they would undoubtedly have the WORST products on the market !!!!
 
W4DNQ Rating: 0/5 Mar 11, 2012 16:53 Send this review to a friend
HE Amp  Time owned: 0 to 3 months
I have purchased many Ramsey kits before and this one is all junk. Just like the rest.
 
K9HTL Rating: 4/5 Feb 7, 2012 12:34 Send this review to a friend
Apprehensive at first but satisfied  Time owned: 0 to 3 months
After reading the reviews I was apprehensive about ordering the QAMP20. But following some of the suggested mods while building it resulted in an amp that works well. I have had success on PSK31, SSB and SSTV using a FT817 to drive it.

Mods performed:
1. Installed small 2 inch fan on lid to blow directly down on heat sinks. Drilled vent holes in front panel in line with heatsink fins.
2. Added ferrite beads to gates.
3. Added 33 mfd cap across C10 to increase TX/RX time delay.
4, Adjusted bias to 0.2 when cold.
5. Added heatsink grease to MOSFETS

I had to rewind T1 and T2 due to turns shorted to the 2 hole ferrite cores....pulled turns too tight!!

The circuit board is evidently of higher quality than earlier versions. No hint of traces lifting.

Power out is a solid 20 Watts with 13.8 VDC as measured at the amp power plug and the 817 set at 2.5 Watts. The 817 sees an SWR of about 1.6.

So far, so good!!


 
KB1NLW Rating: 4/5 Jun 8, 2009 20:39 Send this review to a friend
Must add a Fan  Time owned: 0 to 3 months
I built a 20 meter version and it is working fine on PSK (a continuous high power mode, ALMOST 20W peak and 15w average). However the kit should be considered a starting point needing a few modifications.

A must is the addition of a cooling fan. Without a fan the heating of the output FETs causes their bias current to increase, causing further heating, increasing the bias…… Also take care with the potentiometer, make sure you start with the taper at the R3 end – check with a VOM before powering up. I believe this probably the biggest problem with the kit, so be sure to add a fan. I added a 1.0” square 12 v 0.09 amp DC fan under a 1.0” round hole the top cover and vent holes behind the heat sinks. The tiny fan fits over the heat sinks without a problem.

The manual recommends setting the bias for at 0.25 amp input. I recommend not more than 0.2 amp. Note that there is a steady rise in current as the FETs warm up.

Based on other posts, I also added 10 ohm resistors in series with the FET gates by bending up the FET gate leads and using the PC board holes for one end of resistors and tying the other resistor end to the gate. I also changed R8 & R9 270 ohm resistors to 220 ohm 1w.

One last change was to change to BNC connectors in place of the cheap RCA connectors.

It does appears to work well in combination with my Small Wonder Labs PSK-31 20m. PSK reporter showed reception of signals all over Europe.

(I would not build this without the mods becaue it probably would self distruct)
 
W7RJR Rating: 2/5 Apr 9, 2007 18:00 Send this review to a friend
Followup  Time owned: 0 to 3 months
The MOSFETs provided by Ramsey in this kit were incorrect resulting in multiple component failures/smoke during initial testing.

I replaced the semi-conductors with common ones found at Radio Shack. The IRF-510 MOSFETs at $1.99 each worked like a charm. This amplifier now works. Better quality control will assure a better experience for the end user.
 
W7RJR Rating: 0/5 Apr 7, 2007 15:20 Send this review to a friend
Caveat Emptor  Time owned: 0 to 3 months
Obviously some folks have been able to get this to work! That is to their credit. Despite being an experienced kit builder, I have not.

After hours of troubleshooting, lifting components to test with a multimeter, double-checking for cold solder joints, solder bridges, mistakes, etc., this device will not work! The only schematic you can get is the one that comes with the instructions, which is faded and missing some critical traces.The schematic only provides voltage references for TP1 making troubleshooting that much more difficult. The schematic shows the primary and secondary windings of the matching transformers in reverse. A call to Ramsey Electronics netted a brief conversation with a fellow that wasn't all that familiar with it. He stated that he heard that some incorrect semiconductors had been ordered and perhaps my kit contained some of them.

The PC board is cheap looking but despite a lot of pulling parts to test them none of the pads or traces have lifted yet. I fear that will happen soon.

I will replace all of the semiconductors in this thing (which won't amount to a lot) and see if it plays. If not, it will occupy a proud position in my trash can.
 
NJ3C Rating: 4/5 Dec 13, 2006 18:49 Send this review to a friend
Works fine with mods  Time owned: 3 to 6 months
Despite the poor reviews here I bought it, knowing that I would have to make some modifications to get it to work. Here are my mods:

add 1/2W 10 Ohm R's in series with MOSFET gates
repl C's in low pass filter (C4-C7) w/ silver mica
repl R8, R9 with 1/2W 270 Ohm R's
add 1/2W 270 Ohm R across primary of T2
use #28 magnet wire in T2 instead of #24
use heat grease under MOSFET's

Without the 10 Ohm resistors in series with the gates, my QAMP went into self oscillation when I tried to bias it. I decided to use better, 500V caps in the low pass filter because I did not trust the ones supplied with the kit. Using higher rated feddback resistors for R8/9 keeps them from burning up. The 270 Ohm resistor across the primay of T2 was used it to keep the input SWR down. Wrapping T2 with #28 wire gives you a bit more room and reduces your chances of a short. Finally, the heat grease helps keep the FET's cool.

I have used my QAMP20 in the field now fairly often and have not been disappointed. The FET's get hot but do not overheat when operating CW. I have made a lot of contacts with this amp that I would have never made barefoot with my 2W Wilderness SST. Overall well worth the $50.
 
AD5JN Rating: 0/5 Dec 1, 2005 05:44 Send this review to a friend
Junk  Time owned: more than 12 months
Don't buy it! Pure junk. The thing blew up after powering up. PC traces are cheaply done. I did the required mods but still not working. I put it in the same MFJ junk pile. This was the first and last time I buy anything from by Ramsey. BTW Support from them is zero %!
AD5JN
 
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