Magnum TX2000M Mosfet amp

Weather has been a bit wet so not much work on the tower, but today we received the first batch of the new Magnum MOSFET amplifiers.
The front panel and the rear panel below.
Time to go check them out….
The mobile bracket is good…very sturdy. Internally neat and tidy.
Magnum TX2000 Amplifier under test
Just had time to take it out of the box and set it up with a Magnum S-45 transciever.
Unit is quite heavy and the internal fan runs consistantly when unit is turned on exhausts through slots in the rear panel.
Fan didn’t seem to moving much air but although the unit heats up quickly in AM and FM mode it cools off quite quickly too. Stayed slightly warm during an extended QSO on SSB with 30w PEP input.
As the fan is internal you would need to raise unit up with some rubber feet if using it in a base station so the fan has a gap to suck wind in thru. The amplifier comes with a mobile mounting bracket which I used to raise the unit off the tabletop. Few amps these days come with a mobile bracket.
Front panel is basic with on off, SSB/AM, and RX preamp  rocker switches and a 6 position rotary switch with a weird looking long chrome magnum type channel selector knob on it. I think it sticks out too far and a three position rocker switch would have done the job as well and looked much better.
How often do we change the power levels on an amp?..Not often. In my case we either need an amp in line or we don’t. The lower levels hardley do anything anyway.
I could not notice any difference in output power between position 5 and 6 regardless of mode or input level to the amp.
On many solid state amps of this type the last position is about double the one before it…Not in this case.
Power supply to the TX2000 was set to 14.5v. Power readings on a PEP bird 43 with a 2-30mhz 250W insert
First check input SWR. It was 1:1.5 from 25.2 thru 29.7 which is the limits of the S-45.
The S-45 was putting out 30w FM
On 27.555 FM with 30w input the output was as follows for the various selector positions:
Hardly remarkable.
So what if you have a 10W rig
29.700 mhz with 10w FM drive = 37.5w out
27.555 mhz with 10w FM drive = 40w out
25.165 mhz with 10w FM drive = 42 out
Trying a few different input levels and the power level at 6
Frequency 27.555mhz
50w = 150w out
40w = 137.5 w out
30w = 115w out
20w = 80w out
10w = 42w out
5w = 22.5w out
So 150w was all we could get out of it. (out of the box!) Probably be OK for a bit more in SSB but no point in destroying it. Brochure states 50w max input.
Need to check the lower frequency limits and see how low it can go before the out put starts dropping off.
Checked the limits with an Icom 7000 bird and dummy load. Using the internal meter of the radio to observe the SWR and the output on the bird meter. Input power for these tests was 35w FM.
Input SWR doesn’t start to rise until we drop to 15mhz but the efficiency has already dropped off well before that.
Still ok at 24.5mhz and power had dropped to 110 from 125 input swr still 1.5:1
By 21mhz the out put power had dropped to 95w and input SWR still 1.5:1
Output power dropped off rapidly below 20mhz but the input SWR did not start rising till 15mhz
So in summary; why would anybody buy this?
Well…you want to put it in the car and you need a mobile bracket.
         you don’t want to buy and fit a fan to one of the other amps in your collection
         you have a 30w rig and don’t want to risk blowing up a smaller amp
         you only want to run about 100w in the car cos you have a mag mount antenna
         Cos it is cheap
Well all these facts and figures are great but how do they sound on air?
A test with a nearby station confirmed the S-45 was sounding good and 3-5-7 on the signal meter.
With the Amp in signals were 40 over 9 and the audio remained very good. Just got louder. A big thumbs up to the linearity.
He was impressed and I may have the first sale!
I had set up the 257 with the kl203 to go in the car but I may have to look for a place to bolt in the TX2000M.!!
I guess it is OK…hard enough to find a sweet talking amp these days…I would have preferred a bit more power…but then this is about all you could run with mostof mobile set ups without getting into a lot of effort. I am sure it won’t be long before the 300w version hits the streets..and that would really be sweet.
These should retail for about US$150.00
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14 Responses to Magnum TX2000M Mosfet amp

  1. vincent lacroix says:

    have one and Idont rely know if im gone to keep it she doing 105 to 115 watts with an at-5555 anytone at 35 watt out . dont now if somthing can be done to bring it up a bit do you have an answer for hop so …. thanks

    • dd182003 says:

      It seems that 150w is all they do with 50w in so I guess the 110 or so from the AT5555 is about it! Can’t see you will get much improvement with 150w anyway and the amp will back off as it gets hot unless you have another fan.
      Magnum brought out another version that has 4 transistors with one driving and that gets about 400 out before it starts heating up and backing off.
      You really have to make sure you keep these cool if you want to keep the power levels up. A much better deal than the first amp. Just put a fan on the top 24/7 when in use!

  2. dd182003 says:

    nope.that’s about all you are going to see out of it for that input. Did you find position 5 and 6 the same output?
    A few more watts won’t make any difference at the other end so I would not sweat it as long as all sounds good at the other end.

    cheers Dave

    • vincent lacroix says:

      thank for the info no not reale a difrence from 5 and 6, my tech tells me that it is the best mache for my at-5555 because of they are tow mosfet machine . at the other end they tell me y have 110% mod mabe more….?

  3. dd182003 says:

    Well, it is cheap for what it is but I don’t think the mosfets in your at5555 care a damn what transistors are in the amplifier !!! Best bet for any radio over 25w is the Texas star DX500. If 100w is all you need then the magnum amp will do you just fine too.
    Remember an amplifier is just an amplifier. What goes in one end comes out the other …..hopefully louder. an amp cannot make a signal sound any better, only louder.
    In fact the reverse is more common and an amplifier will cause some degrading of the audio especially in SSB.

  4. Ed, VA3ES says:

    Nice amp, big big for the power it delivers. It’s a perfect match for the average “2-final” export radio. I use one with an AT-5555 with excellent results. Linearity is excellent. 150W is a reasonable power for average use. If you want more power, go to a 4X2879 amp, like the Texas Star DX500 series.

    • dd182003 says:

      Hi Ed!, For what it is it works but for the size you don’t get much out.
      They have a newer version which works much better. 1 driver and 4 in the final. Now they have an amp. Trouble was it heated up and the output really folded back. The internal fan is not worth much in this case and should be augmented with a fan on the fins as well.
      Why don’t they develop a heatsink that would fit on to the body of the device like they have for the processors in computers. Then cool the heck out that as well.

      • Ed, VA3ES says:

        Hi Dave, The problem with an amp with 1 driver is that that device by design has a lower input. Such an amp, (1 X 4) is by nature a lower drive amp. What is the nominal drive for thius new amp?

      • dd182003 says:

        I would assume about 25w but it does have the power selector to drain off the excess into some resistors. To me 25w in is fine..This amp works much better than the first 2 transistor one. The out put is up around 400w for a minute till it warms up and starts dropping back and sits steady around 300w. Still ok for the price! I think more time and effort needs to be spent physically setting the amp up so it runs cooler..Maybe set the transistors onto a copper plate to improve the thermal transfer …it just plain runs too hot for my liking.

  5. Ed, VA3ES says:

    A buddy has one as well, but wondered how he could use the RF preamp stand-alone, without turning the amp on. It’s easy to re-wire the switches to allow the preamp to work alone, but I fear that without the amp in line, the sequencing will fail and the exciter RF will destroy the preamp. Not having a schematic, I’m assuming that without the amp turned on, the relay that switches the preamp out of circuit during TX will not operate. Hmmmm….

  6. dd182003 says:

    Ask Sam for one to try out…

    • Ed, VA3ES says:

      I have an TX2000M myself. Is the amp an actual Magnum product, or is that just another random name some manufacturer used?
      The new 4 device amp – I’d love to see one. Do you sell them? What is the model number?

  7. dd182003 says:

    I Bought them from Magnum. I did send an email to Sam but no response. Will try Eric! I think with a the new product hitting the market place Magnum will need to reinvent themselves a little. Stryker has really come out strong with their new radio and President has a classy 8800 SSb machine, Galaxy/connex has the std CB format down pretty pat so where does magnum go?
    There are just so many choices out there now….I am still waiting for Icom’s 10m rig!!!

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