[AMRadio] A bit of Viking Valiant help


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


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" <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
>>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
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>>
> 
> 
> 
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