[Boatanchors] 6146 vs 6146A vs 6146B or 6146W

[Gary Schafer]

Neutralization IS a problem with some equipment. I have changed several
early model Collins S line and KWM2 radios from 6146A to 6146B tubes. They
have to be re neutralized  and if they don't have the newer neutralization
circuit they will not neutralize properly. There is not enough range in the
capacitor to allow proper neutralization.

I spent many hours trying to tame the finals in the Collins radios until I
realized that they required changes in the neutralization circuit.

I suspect that lots of people just shove the tubes in and are not concerned
about neutralization. Then wonder why the radio tunes funny sometimes.

You can easily check your Collins equipment for proper neutralization by
observing the grid current when tuning the plate thru resonance. The grid
current should dip at exactly the same point of the plate tune capacitor as
where plate current dips. If there is any difference then the neutralization
is not correct. This includes the feedback neutralization too.
Note that grid current dips rather than peaks at plate resonance when
feedback is employed such as Collins uses. 
A radio without feedback will have the grid current peak at the exact point
where plate current dips if it is properly neutralized.

The screen voltage is often a little different in radios with the two
different tubes.

There is a difference in the tubes but I have not seen any radio that
couldn't be made to work with either type. But it is not always a plug and
play process.

73
Gary  K4FMX

> -----Original Message-----
> From: boatanchors-bounces at mailman.qth.net [mailto:boatanchors-
> bounces at mailman.qth.net] On Behalf Of lee
> Sent: Tuesday, July 05, 2011 1:14 PM
> To: Glen Zook; boatanchors at mailman.qth.net
> Subject: Re: [Boatanchors] 6146 vs 6146A vs 6146B or 6146W
> 
> Yes, this is the article I am referring to, Glen and others.  That said,
> maybe Motorola had a problem a zillion years ago because their
> neutralization was fixed in their VHF rigs.  Maybe Collins had a problem
> with too marginal a neutralization cap in their earlier rigs so they put
> in
> a larger more beefy neutralization cap which should have been there in
> the
> first place, even when they used 6146A tubes.  I don't dispute much of
> what
> is written there.
> 
> However, that article has put fear in many a ham when wanting to put B
> tubes
> within Heath, Johnson, WRL, type HF gear.  As I said,  I have done a lot
> of
> it and so has a friend of mine in HF ham gear, not in Motorola VHF gear.
> I
> don't know anything about Motorola VHF problems, nor do I care to know
> about
> them.  I am only concerned with ham HF gear.  We have never experienced
> a
> problem with the B or W tubes.   That is why I asked for members on here
> to
> reflect their actual findings and not always referring to this
> publication I
> find has no bearing for hams wanting to re tube their old HF ham
> equipment.
> I have been receiving a lot of "private" E-MAIL telling me the very
> exact
> thing.  NO PROBLEM.  Anyone on here ever have a problem using B tubes in
> their old Heath or Johnson type equipment?
> 
> I highly suggest list members find out for themselves what can really be
> put
> into your old ham HF gear and forget that misleading Motorola VHF
> article.
> Don't take my word for it.  Try them out and you decide what is correct.
> I
> find the article has no merit for ham HF equipment.  There is no
> neutralization problem either.  I don't think publicized spec sheets lie
> either.  If they don't tell the full story, what good are tube spec
> sheets,
> when picking out what tubes could be used in a design?
> 
> The bottom line is, when you are restoring an old boat anchor ham HF
> transmitter,  using B or W tubes within it should be the least of your
> worries and concerns.
> 
> For you Glen,  I am truly not trying to pick a fight with you.  I
> understand
> your background and experience and what problems Motorola has had in the
> past with their fixed neutralized VHF gear, and also the neutralization
> cap
> change in Collins S-line gear.  I just think the background in your
> article
> has no real bearing when using B tubes in our old ham HF gear based on
> my
> real world experience when using these tubes.  A ham not knowing better
> after reading your article will many times avoid using a 6146B or W
> tubes
> when he needs to re tube his old HF ham gear.  I think that fear is
> misguided and the record should be corrected.
> 
> Lee, w0vt
> 
> 
> 
> 
> 
> "Being the person referred to:"
> 
> "Glen, K9STH"
> 
> 
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