Message	Date	From	Subject
2828	2009-03-30 12:28:30	Stephen Wandling	A 6L6 lasted forever!
I vividly recall noticing transistors creeping into areas previously occupied by perfectly good tubes, back around '63 or so. Pesky little devils. Some of you may recall discussions here regarding the ea3fxf/ea3ghs Flea transceiver and issues with 'obsolete' transistors. I bought some 2N3866 transistors, the specified unit for the Flea, but have come to realize that they are not what they are advertised to be. But, recently I received a couple 2N3553 I had ordered, as Kenneth had some success with these in his Flea. And so did I! For the first time ever, the receive on the Flea was blasting out signals. Pretty heady stuff if you've been working on the rig for months. I tried various FT-243 crystals that I had recently been given and even tried a few CQs. The Flea is a bit tricky to get set up properly and sometimes I was transmitting, but not on the crystal frequency. Ooops! Now this was the 80M version, and since I had been trying various things to get it to work properly, i.e., changes to the transformer and the capacitive voltage divider and couldn't remember exactly what I had changed I decided to convert it back to a 'stock' 40M version. I did this, and the receive didn't work. I eventually checked the 2N3553 and the hFe was down from about 115 to 24. Hmm? I plugged in the other one and Bingo! I have receive!! Very nice. I even heard W7ZOI in QSO and was going to try and work him but he was heading out for a walk. But I did work Sacramento from my QTH about 150 miles north of Vancouver, BC. He was booming in here and gave me a 459 for my 1W signal. The next day I fired up the Flea again and . . . no receive. I check the 2N3553 and the hFe is down to about half at 65. So, it was fun while it lasted. But . . . the 2N3553 can handle 1A and dissipates 7 watts, so I don't think I was abusing it with my 1 watt output. And I ran it with a heatsink. At $5 a pop the 2N3553 isn't cheap but I will probably order more. What I would like to clear up is the mystery of why they have failed? Any ideas? 72 Stephen VE7NSD -- Hunger is not caused by a scarcity of food but a scarcity of democracy - Frances Moore Lappé
2830	2009-03-30 13:03:13	Bill Noyce	Re: A 6L6 lasted forever!
Stephen -- Is there any chance that powering down the Flea causes the base-emitter junction to be reverse-biased by more than 5 volts? Most transistors don't like that ... -- Bill, AB1AV
2831	2009-03-30 13:34:12	Stephen Wandling	Re: A 6L6 lasted forever!
Hi Bill, Here is a link to my Flea page: http://www.qrpedia.com/book/200812/flea-catalonias-answer-pixie I suspect that the diode D1 would, amongst other things, prevent reverse biasing? I tested the diode and its still functioning ok. 72 Stephen VE7NSD Bill Noyce wrote: > Stephen -- > Is there any chance that powering down the Flea causes the > base-emitter junction to be reverse-biased by more than 5 volts? Most > transistors don't like that ... > -- Bill, AB1AV > >

I vividly recall noticing transistors creeping into areas previously
occupied by perfectly good tubes, back around '63 or so. Pesky little
devils.

Some of you may recall discussions here regarding the ea3fxf/ea3ghs Flea
transceiver and issues with 'obsolete' transistors. I bought some
2N3866 transistors, the specified unit for the Flea, but have come to
realize that they are not what they are advertised to be.

But, recently I received a couple 2N3553 I had ordered, as Kenneth had
some success with these in his Flea. And so did I! For the first time
ever, the receive on the Flea was blasting out signals. Pretty heady
stuff if you've been working on the rig for months. I tried various
FT-243 crystals that I had recently been given and even tried a few
CQs. The Flea is a bit tricky to get set up properly and sometimes I
was transmitting, but not on the crystal frequency. Ooops!

Now this was the 80M version, and since I had been trying various things
to get it to work properly, i.e., changes to the transformer and the
capacitive voltage divider and couldn't remember exactly what I had
changed I decided to convert it back to a 'stock' 40M version. I did
this, and the receive didn't work. I eventually checked the 2N3553 and
the hFe was down from about 115 to 24. Hmm? I plugged in the other one
and Bingo! I have receive!! Very nice. I even heard W7ZOI in QSO and
was going to try and work him but he was heading out for a walk. But I
did work Sacramento from my QTH about 150 miles north of Vancouver, BC.
He was booming in here and gave me a 459 for my 1W signal.

The next day I fired up the Flea again and . . . no receive. I check
the 2N3553 and the hFe is down to about half at 65.

So, it was fun while it lasted. But . . . the 2N3553 can handle 1A and
dissipates 7 watts, so I don't think I was abusing it with my 1 watt
output. And I ran it with a heatsink. At $5 a pop the 2N3553 isn't
cheap but I will probably order more. What I would like to clear up is
the mystery of why they have failed? Any ideas?

72
Stephen
VE7NSD

--
Hunger is not caused by a scarcity of food
but a scarcity of democracy - Frances Moore Lappé