[Boatanchors] National NCX-3 Final Bias Adjustment

Wed Jan 22 22:38:50 EST 2020

Carl Heuther, now KM1H, was the National Service Manager at one time and he was the author of the note that I received many decades ago.  He occasionally monitors the National AND Boatanchors lists.

73 de Mac, K2GKK/5
Since 30 Nov 1953
Oklahoma City, OK
USAF, Retired ('61-'81)
FAA, Retired ('94-'10)

NCX-3 and NCX-5 user since 1963

________________________________
From: mvjohn at sympatico.ca <mvjohn at sympatico.ca>
Sent: Wednesday, January 22, 2020 21:21
To: D C _Mac_ Macdonald <k2gkk at hotmail.com>
Subject: Re: [Boatanchors] National NCX-3 Final Bias Adjustment

Very helpful Mac, thank you!

You mention Sylvania tubes were recommended in National Tech notes....any idea where I might find  those tech notes?

Thanks again for the reply and help Mac. I'm hunting down new finals as my installed pair; RCA's, may be weak.

On Jan 22, 2020 10:11 PM, D C _Mac_ Macdonald <k2gkk at hotmail.com> wrote:
The setting which gives you the 50 mA is what you should aim for.  The actual bias voltage is not material.  With fresh 6GJ5 finals (preferably Sylvania according to National tech notes), idle current at 50 mA, and loaded for 300 mA cathode current on 80 meters, you should get 120 to 130 Watts output.  Output on 40 should be about the same and just a bit less on 20 meters if final tubes are properly neutralized.  Proper idle current is what gives best tube life.

73 de Mac, K2GKK/5
Since 30 Nov 1953
Oklahoma City, OK
USAF, Retired ('61-'81)
FAA, Retired ('94-'10)

NCX-3 and NCX-5 user since 1963
________________________________
From: boatanchors-bounces at mailman.qth.net <boatanchors-bounces at mailman.qth.net> on behalf of Mark V Johnson <mvjohn at sympatico.ca>
Sent: Wednesday, January 22, 2020 19:50
To: boatanchors at mailman.qth.net <boatanchors at mailman.qth.net>
Subject: [Boatanchors] National NCX-3 Final Bias Adjustment

Team,

I have a National NCX-3 transceiver on the bench and I have a question about
the final tube bias adjustment.

The transceiver has good output and I've made contacts with it, but the
control grid bias voltage spec is -45 to -55 VDC. If I set the bias adjust
pot on the rear of the chassis for max, I can get the bias down to -51VDC.
On spec. However, when setting the bias pot as per manual: key mic with no
output and adjust pot for 50 to 60 ma on meter, the actual bias voltage goes
to  61VDC and my  actual RF output drops.

I have several National Service Bulletins and they cover a wide range of
changes/improvements but nothing related to my problem.

The rig has 6GJ5's installed.

Is there another service bulletin related to this? Should I adjust bias by
setting the DC voltage or by using the IC meter?

Many thanks.

Mark V Johnson

VE3LU/VE3DJU

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