Re: RF power chain mods and improvements..

Jerry Gaffke
 

Allison,

Yes, surface mount parts into current boards would be tough.
The to-39 and to18 parts are fine for current rev boards, no point in saving 
a couple bucks and then spending hours trying to whack them into place and heatsink them.

But nice to think about what hfsignals might do in the future.
If the smt 2n5109 is cheap or an smt 2n2222a works in the driver stage,
the additional cost in parts might be held to a dollar or so.

Could be that the IRF510's and others will behave better at 30mhz if laid out differently.
And not having so much RF on the main board might even help those mixers out?
If so, a Q30-to-IRF510 daughterboard makes good sense.
And as you say, many here will prefer that to swapping out a half dozen transistors and rewinding torroids. 
Especially since with the daughterboard it could be easily reversible, back to a stock uBitx.
 
Jerry


On Sun, Jun 10, 2018 at 01:24 pm, ajparent1/KB1GMX wrote:
Jerry,

The DXT2222A-13 is a possible choice for pre-driver as the power is fairly low.  For the driver
the board layout to get the tab on enough copper is nasty space wise.  I've used that part
and its otherwise a good SOT89 2N2222A maybe a tiny bit better (lead inductance is smaller).
It would be hard to apply to the current V3 and V4 board. 

The SMT 5109 is not useful for the same reasons [board layout] for the driver. it
would work a bit better for the pre-driver. 

NOTE on SOT89 the pinout is BCE and the boards are EBC so attaching them to existing
boards would be very messy with lots of cutting and jumpers even for test reasons. They
would also need a flag to radiate the heat (copper .020 thick by .25 side and .4 tall.).
Someone else can do that for a test.

The BFR106 works for Q90 and also in the 45mhz IF amp section very well.  Its not a choice
for other parts of the radio. As more power capability is needed or 3904 is fine.

One possible layout I looked at was strip the power amp completely Q90 though IRF510s
and have a board above the main board carry the input filters, improved amp, then 
using the output  filters on the lower main board. Two pieces of coax and a few control
lines. That and other added features as there would be space.  That would make an
upgrade far easier as its a whole board and wires. 

Allison

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