[Boatanchors] 6146B

[Garey Barrell]

Pete -

I think the problem with the early Collins transmitters was that they 
used a compression trimmer for the neutralization.   The trimmer cap 
"burned up" because of RF current or ?.   The later transmitters used a 
small air variable trimmer and works fine.   I would guess that the "not 
holding neutralization" was a result of the cap heating up?

I'm not sure why the B version generated so much more circulating 
current / peak RF voltage in the older neutralization circuit than the 
older versions.  Someone said that the interelectrode capacitances 
weren't all that different.  Perhaps the physical arrangement of the 
elements with respect to external metal shielding was the culprit.

I have used B version tubes in Viking IIs and Valiants with no problem, 
and in the DX-100 and DX-40 also.   I think the Valiant had a "fixed" 
neutralization circuit, but I don't think any of the others have any 
neutralization, relying instead on loading the final grid circuit.  

Just one more reason why grounded grid stages became so popular!! :-)

73, Garey - K4OAH
Atlanta

Drake R-4C Service Information CD
http://www.k4oah.com
 



peter markavage wrote:

>Absolutely Jim. My Apache has a crude "neutralization wire" that comes up
>through the chassis between the 6146's, that you manually move closer or
>further away from either tube. I believe CQ or QST also had an article on
>DX-100 mods that included adding neutralization. If you have a rig that's
>running 6146's, and it has no neutralization adjustment, you should
>figure out a way to add it. It's also not clear to me, why, after doing
>neutralization to a final at a high enough frequency with B's, it won't
>"hold". At least I've never seen that happen, but then again, I don't own
>any Collins transmitters. I didn't think there was "creepy" capacitance
>in those tubes.
>
>What really should be done, is that someone should take the initiative to
>gather the data for rigs that exhibit problems with B's or W's in the
>final and define a resolution or fix, so that going forward, people can
>use the data to resolve the issue if they perceive they have a problem
>using them. The answer, don't use them, shouldn't be the answer. But,
>then again, "do you feel lucky today", works for me at times.
>
>Pete, wa2cwa
>
>On Thu, 8 Dec 2005 10:52:45 -0600 "Jim Wilhite" <w5jo at brightok.net>
>writes:
>  
>
>>I put 6146Bs in my B&W5100B and reneutralized it.  It works just fine 
>>and 
>>have not had problems.  Remember most manuals say to redo the 
>>neutralization 
>>when changing finals anyway.
>>
>>On radios with no neutralization that is different.  The DX 100 can 
>>be 
>>modified to add neutralization, the Valiants have it.  Don't know 
>>about any 
>>others but it shouldn't be a great problem to add..
>>
>>73  Jim
>>W5JO
>>
>>
>>
>>    
>>
>>>Many of the older transmitters actually did not have
>>>any means for neutralization of the 6146 final(s) and
>>>that definitely adds to the problem.  If the 6146B
>>>tubes can be neutralized and if that neutralization
>>>"holds" then they can safely be used in the older
>>>transmitter.  Unfortunately, not every transmitter
>>>"holds" the neutralization.
>>>
>>>It would have been a lot better if RCA hadn't used the
>>>same basic nomenclature with the 6146B and if they
>>>hadn't originally said that the 6146B could replace
>>>the earlier versions without any problems.
>>>
>>>Glen, K9STH
>>>      
>>>