[VHFcontesting] FYI - DB6NT transverter failures

[w8zn at comcast.net]

Hi all, 



For those who use DB6NT transverters, I've had three failures on three different transverters all traced to the same part. DB6NT uses a FET for the main T/R switching which is a BUZ171. There are two versions of this device depending on which transverter you have. Some were TO220 and others were SMT. This FET switches 12v from the rx section to the tx section and drives a 8 volt regulator. It also outputs 12v to a feedthru cap to the outside world. If this FET fails, rx still works but you'll get no transmit and no current increase when you ground the PTT pin. In my cases, I think the failure was helped by me running external 12v relays off the +12tx line. The relays only draws about 100ma, but these FET's aren't heat sinked in any way and on my 1296 transverter, the board was actually discolored where the device is showing me it was running hot. 



I've searched high and low for the BUZ171's and unless I want to spend $250 for 250 of them, they are not available in the US, only from Europe. I did find a direct replacement that is available in the US, a 2SJ438. In small quantities, less than $2 each. They should be here tomorrow and I'll let everyone know if this is a good replacement. 



If anyone knows of a source for TO220 BUZ171's here in the states, let me know. I don't have a problem ordering from DB6NT direct, it just takes two weeks to get anything from them. 



Terry - W8ZN