"Stray Dog" wrote in message
r.org...

On Fri, 29 May 2009, Will wrote:

Date: Fri, 29 May 2009 23:13:33 GMT
From: Will
Newsgroups: rec.radio.amateur.boatanchors
Subject: neutralizing new tubes

Hi all ,
I am replacing the 7146's on my Kenwood 520s and would like to know if
there
is a certain proceduere I need to go through to neutralize the tubes for
optimum performance and maximum life.Thanks in advance .

PS I'm kinda new at this so be gentle

You might ask yourself, first, are the old tubes really weak? i.e. less
to much less than 50 watts of carrier output, as measured with a wattmeter
into a good load (dummy or real).

You might ask yourself, second, what bands you plan on operating on.

If low (160,80,40 meters) you might not need netralization. All the old
handbooks mention that self-oscillation is a problem at the higher
frequencies.

There are two classical methods to test for neutralization (after you put
in the new tubes):

1. With rig output into a dummy load and wattmeter, can you get RF output
with excitation removed, at some setting of grid drive tuned circuit or
plate output tuning.

2. You look at grid drive and sweep the plate tuning through its range: if
the rig is not neutralized, then you'll get a dip or blip in grid drive.

You can't do this directly with the 520 since it does not register grid
drive on the finals. But, you can adjust the drive level knob to at or
near zero output. Then, you fiddle with grid drive tuning knob AND,
separately, plate tuning knob, and if plate current goes up high and RF
comes out (as shown on the watmeter), then you got self-oscillation in the
finals. Bad news. You'll have to adjust the neutralization as per the
proceedure.

Many old rigs did not have neutralization. DX-100, Viking Ranger, etc.,
were all 6146 rigs with no neutralization. The Drake twin lines (6BQ6s in
final) did have neutralization. Sometimes they worked, sometimes not. I
had a single 6146 DX-40 transmitter that I discovered went into final
oscillation if I removed grid drive. Bad news. I made my own
neutralization wire from bottom of the chassis to the top and moved it
closer or farther from the plate of the 6146 until the self-oscillation or
grid drive flicker stopped when I tuned the plate circuit. All trial and
error.

Good luck

Thanks for your input and everyone elses replies. I did a google search and
came up with this URL http://www.k4eaa.com/faq.htm

It was extremely helpful and it gave me a better idea of what I need to get
back on the air. Problem now is I don't own a dummy load or RF
millivoltmeter so til then I guess I'll be off the air . This sux.