[AMRadio] A bit of Viking Valiant help

Larry Szendrei ne1s at neandertech.com
Sun Aug 28 08:24:51 EDT 2005


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).


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" <jpl15 at panix.com>
> To: <amradio at 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
>>   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!
>>John  KB6SCO
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