Sent to the reflector on behalf of Robert, F5UL in Senyod, France:
Hi the list
Some months ago, I got a PA blow-up and with the help of the list and
particularly of Gary, it was solved for I thougth a long time. Well it
happened again and the results are differents ! I replaced both 2sc1969
and also Q13 who was shorted CE which was the cause of PA loss!
I end up with a power out of 12/13 w continus with an collector curent
aroud 5 A, and after search an auto-oscillation around 2.5 Mhz was
found. The power control have no action CCW or CW position it's the
same. It's the 2SC1969 the culprits, or at least their presence, if I
remove them the instability is not there, and the driver output is about
5 volts PEP on each base ( 9/10 V PEP base to base). At this point the
signal is clear in the control receiver CW or SSB.
I tried other transistor (2sc1969, 2sc1971, MRF476) to no avail, always
this square wave signal with frequency variation from 2 Mhz to 3.5 Mhz,
but always full +/-12V PEP.
I removed all components, up to Q5 circuits, put them back in after
rewinding the cores with no results.
So I look for some help with this new problem. Can the DAC converter be
involved?
The receiver is working OK, the PA bias is staying with 0.62 volt. With
only the driver the curent is around 0.480 A but more than 5 a with the PA.
73/72 from F5UL
_______________________________________________
Elecraft mailing list
Post to: [email protected]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com
