YES!!!!
I had this problem with my Ranger when I first got it on the air about
20 years ago. I had a 6146B in the socket, and it displayed the same
symptoms. The tube heats up, starts to release gas (I'm trying hard not
to make a joke here!), plate current goes up, and then starts to release
more gas, going into a thermal runaway condition. It is perfectly happy
with 6146's or 6146A's. A "gassy" tube may also be responsible, no
matter which flavor of 6146 it happens to be.
You may also be getting a bit more plate voltage with the solid-state
diodes that with the mercury vapor rectifiers that may be putting you
over the edge, which may be making matters worse (but is probably not
the primary cause).
73/GL,
-Larry/NE1S
GBrown wrote:
Just a wild a-- guess, but I thought that the Valiant used only 6146's, not
the "B" 6146. It is my understanding that sometimes subbing in the "'B" for
the early 6146 just doesn't cut the mustard.
Regards,
Gary...WZ1M
----- Original Message -----
From: "John Lawson" <[EMAIL PROTECTED]>
To: <amradio@mailman.qth.net>
Sent: Saturday, August 27, 2005 1:56 PM
Subject: [AMRadio] A bit of Viking Valiant help
I'm in the middle of a long, slow project to get my Valiant back in
service. I've changed out the bigger power tubes, solid-state replacements
for the 866s, and partially re-capped the rig, specifically the RF power
section.
After finding (expensively) out that 'W' 6146s just don't work, I
replaced the finals with new 'B's and power is now being transferred to
the antenna / dummy load.
Main bug:
On the bands below 20M, however, and getting 'worse' as the frequency
gets lower, the rig "runs away" after 15 - 30 seconds - the plate current
rises fatser and faster and then needs to be shut down, lest another set
of 6146s gets wasted. ;}
I have neutralized the transmitter per the manual, seems ok. Bias also
set per sepc. LV rectifier tubes have been chacked (on a Weston 686) and
seem within spec, though their performance under load is measurable only
in situ.
I left the doorknob cap alone because it's fine electrically and not
cracked or discolored.
Do the sypmtoms sound familiar to anyone? Before I spend a bunch more
hours wearing out the transmit switch, I thought I'd ask those who have a
lot more experience than I do with the Valiant.
I can add more info/observations as needed, specific caps replaced,
etc.
Thanks all!
Cheers
John KB6SCO
______________________________________________________________
AMRadio mailing list
Home: http://mailman.qth.net/mailman/listinfo/amradio
Help: http://mailman.qth.net/mmfaq.html
Post: mailto:AMRadio@mailman.qth.net
______________________________________________________________
AMRadio mailing list
Home: http://mailman.qth.net/mailman/listinfo/amradio
Help: http://mailman.qth.net/mmfaq.html
Post: mailto:AMRadio@mailman.qth.net
