Tech tips on the new DX33HP

[GRTS]

As some of you know the old DX33HML went out of production on Nov. 2006 and later replaced with the new DX33HP model. The only real changes made was the switch over to IRF520 mosfets, heavier AM modulator (2SB827) and blue leds. One characteristic of the IRF520 mosfet is the higher gain (hFE) at 25-29Mhz over the 2SC1969 bipolar transistors. Here is a tech tip that will increase peak power on the DX33HP models and not void the factory warranty.

This update will allow you to set the max carrier @ 10 watts with peaks of 50+ watts and no flat-topping on the scope.
Locate resistor R178 and replace it with a 1k ohm 1/4 watt.
See thumbnail below.


Next is the lack of a dimmer control on the DX33HP. The next production should have a dimmer control installed. Until then on the current production models you can replace jumper J303 on the channel PCB with a 1k ohm 1/4 watt resistor which works great for both day and night. This update also does not void the factory warranty and is recommended especially for night driving. See thumbnail below for the location of J303.

 

[ss8541]

a little more power

hope ray does not mind me adding a little something we have been doing to all our 'from the factory' mosfet radios.

steve has been adding a 25v 10,000uf cap (available at westgate labs) between the main supply rail that feeds the 2sb827 and the ground rail of these radios. he uses 16ga wire (anything smaller will not give the results you want) to wire the cap to these points. this reduces a lot of the voltage drop on modulation peaks. he sees about a 10w pep increase from pure stock radios (that have been peaked and tuned of course). these measurements have been made with an hp8920a service monitor. where ray is seeing 50+ watts pep, we are seeing in the neighborhood of 60+ watts pep after installing the capacitor. this is with the radio being operated at 14vdc.