I have put a picture of the Palomar high drive amp next to an old texas star DX1600. I am not sure what the 450 FET means but I thought I would try the high drive version of this amp as i thought it might prove to be interesting. from past experience with these amps using the 7530 mosfet transistor was that they worked OK but just got too hot. Whats too hot? I figure if I can’t hold my hand on it for very long it is too hot. In the past I have tried a 2 transistor version and a 1 driving 4. both worked OK but needed lots of additional cooling. I figured these 4 in parallel versions run with just a few watts might give a couple of hundred watts nice and easy and not get too hot. And the 21w PEP of the cree seemed just right.
A brief description: it has 3 power levels, lo mid and hi, a pre amp and an on/off switch. The blue LEDs are really bright. No delay switch for SSB. It seemed the delay is built in because I did not notice any Jitters on SSB. Physically it is small, the size of a conventional 100w amp. Fins on the heat sink do not protrude much. Not a lot of surface area at all for an amp rumoured to be capable of 400w.
So how did it work? Real life tests into an antenna at 27.5mhz. Input power 21w SSB. Radio, Cre8900. Between the radio and amp we installed a pretty tight 27mhz band pass filter. (Morgan manufacturing M-411-CB)
Test into a dummy load and all good: low 55w , mid 90w and hi 120w pep
This is what we got on the antenna: low : 55w SWR 1.23:1,
Mid 87w swr 1.2 :1,
Hi 184w swr went up to 2.8:1.
I put a low pass filter after the amp and got these results. low : 55w mid : 90w Hi: 120w swr remained constant at 1.2 :1.
So when driven gently (21w pep) on low or mid the amp is OK up to 100w …but on high level all hell breaks loose. An additional 70w of RF somewhere is being produced and the antenna doesn’t like it. Hence the hi swr. The lo pass filter cuts it off and in so doing reduces the output to 120w on the frequency of choice. I guess on a dummy load everything looks pretty good…no swr from a dummy load. No wonder the amp gets hot! What waste. 30% of the output wasted. On air reports the signal improved and the SSB audio was good with the amp in play so it seems it is still reasonably linear. The maker needs to put the output on a scope and make changes to the design to curb the harmonics or what ever they are. They need a bigger heat sink and more cooling. I don’t think they are worth buying to be honest. Better off with a KL 203 or KL503. If you want power then get a texas star DX 500. I don’t think these can survive in use for very long even without the chronic 30% out of band transmissions. It looks like we have a 100w amp! Keep it at 100w and you might be OK.