PA transistor swap - advice needed.

Animal · Post by **Animal** » Friday 30th May 2008, 20:24

Any advice appreciated guys.

Can a 2SC2290 transistor be replaced with a 2SC2879???

I looked at the data sheets for both & the voltages are all identical between Collector/Emitter/Base.

The only difference I can see is the collector current is higher (5A more) on the 2879 (the 2290 is 20A) & the input power is higher on the 2879 (can take 10w PEP)

Will I need to upgrade the driver & re-align the TX coils???

The radio is the Cobra 200 GTL DX (Rev 3)

Many thanks.

speedracer6g · Post by **speedracer6g** » Sunday 1st Jun 2008, 4:20

I was looking at the data sheets for the two transistors. The only Difference i see is the collector output capacitance is about 200pf higher wich isnt a big obstacle i would think, however the higher drive that it requires is a different story. You may want to look into upgrading the driver to a mosfet like the irf520. You may be able to get the extra drive you need just from that. I would think it would be possible because the mosfets have a higher gain and you should be able to squeaze 10 watts drive pretty easy out of it. I will look into it myself because that would make a nice upgrade to go from 60 pep to 100pep. The only other problem may be heat.

Mike

MIKE

speedracer6g · Post by **speedracer6g** » Sunday 1st Jun 2008, 4:45

what final is being used in the driver section at Q74? If it is the rd6hhf1 it is only a 6-10 watt driver you will need more than that do drive the new transistors. I would like to see this work though.

MIKE

Animal · Post by **Animal** » Sunday 1st Jun 2008, 5:48

It's the RD16HHF1 Mike & whilst the drive is lower than that needed to get full output from the 2879, the IMD figures are lower & I'd guess they'd run cooler not being driven hard - that's the logic of the swap, not the higher output (but if I get more as a by-product then it's a bonus!)

ATB

Steve

timrim · Post by **timrim** » Sunday 1st Jun 2008, 6:00

They can be swapped but the resistor/capacitor feedback between the collector and emitter usually need to be changed to allow for a somewhat greater feedback, or the 2sc2879 can self oscillate. I dont have the exact values for the resistor and cap handy, but I will see if I can give you a recommendation later.

Rick · Post by **Rick** » Sunday 1st Jun 2008, 9:33

Try and stay with 2290 as 2879 will be more trouble they it is worth.

Animal · Post by **Animal** » Monday 2nd Jun 2008, 17:27

Thanks Rick - it was just a thought (the idea was to reduce the heat generated by under-driving the 2879 but getting a similar output to the 2290's)

The 200 doesn't have a fan & relies on the heatsink alone.

ATB

Steve

The Defpom Forum, for RadioMods, S&M Software and Music by The Defpom

PA transistor swap - advice needed.

PA transistor swap - advice needed.

Re: PA transistor swap - advice needed.