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[W1JPP]

I’ve watched this video on neutralizing tubes in a kenwood hybrid using a receiving radio and I have a couple questions

https://youtu.be/cCWueaSGFwg

1. He shows the transmitting radio as being set to “tune” as opposed to cw, usb or lsb. What do you set the receiving radio to?

2. In the video, he says the transmitting radio should be connected to a dummy load and the receiving radio should not be connected to an antenna. So how does the receiving radio receive anything to deflect the S meter.

Is it receiving some “static” coming from the tubes not being neutralized.

3. He says set the receiving radio to max attenuation. Does that mean set the af gain all the way so the S meter is peaked and you cant hear anything and then watch for it to go down?

[AC2EU]

The objective is to minimize the output signal coupling through the finals.
"static" I would assume indicates a lack of signal and minimal or no S units, which is a good thing.
It works like any other CW transmission.

[ZS5WC]

 :)You are on the right path.
The idea is the neutralise the internal capacitances of the tubes by applying negative feedback via the neutralising cap.
This will stabilise the finals and stop runaway oscillations.
Remember to turn off Screen Grid switch on back panel after tuning up rig on 10m into dummy load.
At this frequency the adjustment will be most effective.
So then there are two ways: monitor that frequency on ssb on another rig with attenuators engaged, and perhaps fly lead over coax to dummy load into that radios antenna socket.
Send small (very low) carrier on tune position on your Hybrid, and tune other radio till you get heterodyne beat audio and S meter deflection.
You might have to add / remove att. for proper deflection, around mid scale.
Adjust neut. cap. for minimum deflection on S meter.

A better way and easier, is to connect 10 times probe and scope to hybrid antenna socket with dummy connected, TX with either low or no carrier on ssb, turn neutralising cap for minimum deflection on scope.
Remember scope must be adjusted for decent deflection on carrier and noise for adjustment.
After adjustment, remember to switch on Screen Grid switch again.
Use as little carrier on tune pos as possible to give good deflection on scope.
Be careful with Neutralising cap, use insulated tool, and don't force it.

73 de William
ZS4L / ZS5WC

[W1JPP]

:)You are on the right path.
The idea is the neutralise the internal capacitances of the tubes by applying negative feedback via the neutralising cap.
This will stabilise the finals and stop runaway oscillations.
Remember to turn off Screen Grid switch on back panel after tuning up rig on 10m into dummy load.
At this frequency the adjustment will be most effective.
So then there are two ways: monitor that frequency on ssb on another rig with attenuators engaged, and perhaps fly lead over coax to dummy load into that radios antenna socket.
Send small (very low) carrier on tune position on your Hybrid, and tune other radio till you get heterodyne beat audio and S meter deflection.
You might have to add / remove att. for proper deflection, around mid scale.
Adjust neut. cap. for minimum deflection on S meter.

A better way and easier, is to connect 10 times probe and scope to hybrid antenna socket with dummy connected, TX with either low or no carrier on ssb, turn neutralising cap for minimum deflection on scope.
Remember scope must be adjusted for decent deflection on carrier and noise for adjustment.
After adjustment, remember to switch on Screen Grid switch again.
Use as little carrier on tune pos as possible to give good deflection on scope.
Be careful with Neutralising cap, use insulated tool, and don't force it.

73 de William
ZS4L / ZS5WC

Thank you.

So my only option will be option #1...using the other receiver.

As a test, I have another kenwood hybrid, that works fine...and I went thru the process of tuning to 28.5 into a dummy load....and then I flipped the SG switch to the down (off) position on the hybrid...so the settings on that rig were lower left knob set to tune (as opposed to cw, usb or lsb)....and the meter knob on the upper left by the meter set to RF (as opposed to ALC or IP or HV)....

and on my receive rig (an icom 756 proii) I tuned to 28.5, unplugged the antenna, put that rig on CW...I also put my RF/SQL knob to 12 o'clock position (the way I have that knob functioning is both RF and Sql....at 12 o'clock RF is full (open/loudest) with no blocking - if I moved the RF knob counter clockwise from 12 oclock towards say 9 oclock, it begins to block noise......(at 12 oclock there is no squelch)

when I hit the send on the hybrid, I did hear the tone on the rx rig....and I had some meter deflection...

so I'm guessing when I go through this same process with the hybrid I'm putting new tubes in, as I slightly turn that adjustment screw to the left and right, I will see the meter go up or down on the rx rig (icom)....and my goal is to stop where I get the lowest meter (s unit) deflection...

I did fabricate myself a screwdriver out of a 12" wood dowel...and I put some resin (thin coat) down by the last few inches for strength...I tested it before applying the resin, with the rig off so no shock danger, and was able to turn the screw back and forth without any negative effect to the wood dowel tip...so I'll use that when I make the adjustment.

If I have any of this wrong let me know...but I think I understand it now...

Thanks so much!

[W1JPP]

all working now - put in the new tubes...set xmitting radio with new tubes to "tune" position and "RF" for the meter selection...

and the receiving radio to the same frequency 28.500 and set to usb...

keyed the xmitting radio, and used my fabricated wood screwdriver to adjust the screw by the tubes for the lowest s meter deflection on the receiving radio...

all working fine...

I did have to take off the vfo knob and dials under that to calibrate the dial with the digital readout...I found this video online that made that job easy - never would have figured it out without this video...

https://www.youtube.com/watch?v=39Jg2dPn_Fk

now my old ts-820s is working great...

[ZS5WC]

 :)Great news!. 73 de William
ZS4L