Folks:
I had a similar problem some years ago on my FL2100. One tube glowing red
plate all the time, and plate current indicated. I I found the grid
resistors cracked, and a maybe 1/2" hole perfectly located on the grid, at
the bottom end. You could see it by looking up the tube from the bottom.
The hole is where the current is undoubtedly pouring through to the plate.
I also found the grid resistor cracked.
I was told that the design of the bias circuit just barely cuts the Ip off
during receive. George Badger, of Svetlana, has a fix, a tech bulletin
probably accessible on the web, that increases the cutoff bias on the 572Bs.
I was also told that newer 572Bs sometimes have more gain than older built
572Bs, and in the FL 2100, may oscillate, even in standby. Heavier cutoff
bias fixes the problem.
73, QRO, De Pat AA6EG aa6eg@hotmail.com
>From: "Osten B Magnusson" <sm5dqc@algonet.se>
>To: <amps@contesting.com>
>Subject: [Amps] Addition to FL2100z problem
To: <amps@contesting.com>
>Date: Tue, 8 Apr 2003 16:06:11 +0200
>
>
>
>Hello again!
>
>I changed the tubes between sockets, first it was the tube
>at left that became ''red'', when changed it's the same one
>now in the other socket. So it's obvious I have a bad tube,
>it's Taylor 572B's from 1994 production.
>
>I think I have a pair of Cetron tubes, but don't want to put
>them in until I get to know the reason for the following:
>
>In addition to the bad tube, there seems to be a bias problem,
>why does the FL2100z shows 50 mA Ip in ''stand by''?? That
>it's only 60 mA in ''operate'' - no drive - can probably be
>adjusted.
>
>The first notice of the problem was that my TenTec Corsair II
>''shut down'' - the power supply security function - at times,
>never happened without the amp.
>
>Maybe this is to ''simple'' for this reflector, but I'm a old DX'er,
>I have not built or worked with amps for many years... I have
>an amp project - KW for 160 and 80 with one tube - but DX
>takes too much time!!
>
>73 de Osten SM5DQC sm5dqc@algonet.se
>
>
>
>
>
>
>
>
>_______________________________________________
>Amps mailing list
>Amps@contesting.com
>http://lists.contesting.com/mailman/listinfo/amps
_________________________________________________________________
The new MSN 8: advanced junk mail protection and 2 months FREE*
http://join.msn.com/?page=features/junkmail
|