[Johnson] Viking Thunderbolt

[garyschafer at largeriver.net]

Hi Steve,
I do not own a thunderbolt. but to neutralize you want to watch the grid
current as you tune the plate tune cap.
You should see a peak in grid current at the same time you see the plate
current dip.
You may have a more sensitive reading if you do not load the plate to full
output when neutralizing. 

If you watch which side of the plate dip causes the grid current to go down
you can determine which way to go with the neutralizing cap. When you see
the grid current go up when moving the plate in the same direction, that
means that the neutralizing cap needs to go the other way.
This should be done on 20 meters for balance on all bands.

73
Gary  K4FMX

-----Original Message-----
From: johnson-bounces at mailman.qth.net
[mailto:johnson-bounces at mailman.qth.net] On Behalf Of Steve H
Sent: Monday, May 22, 2023 10:50 AM
To: johnson at mailman.qth.net
Subject: Re: [Johnson] Viking Thunderbolt


Anyone out there do neutralizing on their Thunderbolt?

The manual says to I guess throw a cw carrier on 20m and I guess apply drive
so you get 20mA of grid current tuning up, I suppose into a dummy load with
max power?

I decided to try the Kenwood way , so I installed a screen grid switch so
you could monitor output leakage with a wattmeter with no screen voltage.
With the plate voltage applied, I saw anywhere from 8-10W leaking through by
varying the drive on the 80m band.

It became tedious trying to move the neutralizing cap even through the hole
I drilled for access in the top cover so I opted to retune into a dummy load
and saw only 600w max from the linear, and the corner tube was glowing red,
the other didnt seem to be working much at all, so I guess that was about
half power and neutralizing was way off.

I set the cap to max capacitance, then backed off about 2 turns, and
retried. Now the other tube was glowing just like the other had, and I
redipped and now could get 1100W on the meter via cw carrier.

A few more tests resulted in a strange problem, after I removed the drive
signal, the plate current remianed where it was for 1100w output and the
tubes continued to glow. I had thought my TR relay stuck, but I keyed and
unkeyed it no problem, so I guess this was self-oscillaiton?

I went back and backed off another 2 turns on the neutralizing cap, and now
I have not seen that problem.
So I am left to believe perhaps I was on the extreme edge since I was on max
capacitance, and working my way backwards.

Since I was on 80m, should I neutralize on all the bands up to 10m?

Steve Hearns
KA2PTE






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