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Thread: Neutralizing 6146 tubes

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  1. #1
    Join Date
    Jul 2005
    Location
    Fort Pierce Florida
    Posts
    106

    Default Neutralizing 6146 tubes

    I am about to replace the 6146 tubes in my TS 530S.
    I don't have a sensitive RF Multi voltmeter like the manual calls for. I bought the radio in 1983 and I think I have my $ worth with the tubes.
    Does anyone have any suggestions?
    It will be much appreciated.
    Thanks,
    Jack

  2. #2
    Join Date
    Feb 2002
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    Right here
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    Default

    Have a look here. The procedure is the same for the TS-520 or TS-830.

    http://forums.qrz.com/showthread.php?t=251165
    I'm sorry you don't have the experience or understanding to realize that others possess a skill set that you seem to dismiss as fantastical.

  3. #3

    Default Neutralizing 6146 tubes

    I put some used S2001A's in a TS-820S I have been working on and used a 100 MHZ Tek scope to measure the output voltage so I could neutralize them. This was easier than makiing up an RF probe and using one of my PSM-45 digital multimeters.

    But I found that with a scope, readable down to a few milivolts, it is possible to set the voltage output at the antenna jack (finals turned off) not just to minimum but to ZERO! And this does not appear to be good.

    So don't go too low. How low I do not know. And the point where you have shut everything off changes with different bands so check things on all the bands before you button everything abck up.

    Good luck - and try not to electrocute yourself, Suggest you get a 1/4 in dia wooden dowell and file the end down to a flat screwdriver blade to use in reaching the adjustment cap.

  4. #4
    Join Date
    Apr 2005
    Location
    Melrose, Scottish Borders
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    4

    Default

    Properly neutralised finals will give a nice symmetrical increase in plate current on either side of the dip at resonance. Use a little drive, light loading and dip will correspond with maximum power out.
    I have always neutralised for the above using a well insulated tool.
    If adjustment is well out best to first neutralise on 20m then give final tweak on 15m. Much easier to do than to explain with words.
    If the increase in plate current either side of minimum is not the same then neutralising is required.
    Also if maximum output does not correspond with dip same.

    If rig won't neutralise most likely final tube(s) need replacing.
    With most sweep tubes you will need to neutralise with the tubes oriented in their working position.
    Equipment with proper finals like 6146 can be neutralised with the rig on its side which can be much more convenient.

    Good luck & 73, Bob GM4CID

  5. #5
    Join Date
    May 2007
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    Etna PA
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    2,858

    Default

    Another method is to listen to the feedthru on a second receiver and adjust for minimum.

    Rege
    Now my mistakes travel at the speed of light!:cool:

  6. #6
    Join Date
    Feb 2006
    Location
    Lee's Summit, MO
    Posts
    485

    Default

    Quote Originally Posted by W4JJA View Post
    I am about to replace the 6146 tubes in my TS 530S.
    I don't have a sensitive RF Multi voltmeter like the manual calls for. I bought the radio in 1983 and I think I have my $ worth with the tubes.
    Does anyone have any suggestions?
    It will be much appreciated.
    Thanks,
    Jack
    The 70 year old tried and true method is still the best.

    1. Tune up the tx in the center of the highest band you use, I use 21.3mhz.

    2. Power down, unplug.

    3. Open it up and disconnect the Plate voltage and the screen voltage in such a way as not to interupt the RF path.

    4 Plug it in, put a 50 ohm load on the antenna jack, power it up without readjusting plate or load tuning and increase the drive untill you get an indication on what ever metering device you are using.

    NOTE: Metering device, I use a scope I just lay the probe on top of the PA inclosure. You can use a grid dip meter, field strength meter, millivoltmeter, or the S meter on a nearby receiver.

    5. With an insulated tunning tool adjust for minimum RF energy on the metering device.

    6. That's it your done. Power down umplug and reconnect plate and screen voltage.

    If this doesn't work then you have a problem in the PA. Most likely the neutralization cap is bad.

    73 Walt.

  7. #7

    Default

    There is no need to disconnect the final tube's PLATE and SCREEN voltages in the TS-530.

    On the rear panel is a slide switch labeled "SG". Place this switch in the "OFF" position and follow the neutralization procedures in the TS-530's Operator's manual, page 26 paragraph 6.4.

    If you do not have the operator's manual you can download it at the following link:


    www.n6wk.com/kenwood/

    or from Kenwood's website at:

    http://inform3.kenwoodusa.com/Manuals%5CTS-530.pdf


    Once the neutralizing procedures are completed set the rear panel SG switch to ON and you're done.

    73s
    Mike
    W5RKL

  8. #8

    Default

    I dont understand the comment that zero voltage is no good?? That would hold true if the cap was shorting but otherwise you want whatever minimum you can get.

    I use a spectrum analyzer these days but a seperate receiver has always worked in the past for all the classic CW/SSB rigs Ive owned since SSB and linear finals came along.

    Carl
    KM1H

  9. #9

    Default

    If you're using Chinese 6146B tubes, remember to set the bias to 30mA, not 60mA. This will prevent the overheating/melting of the tubes. This of course is done after any other alignment procedures such as neutralisation.

  10. #10

    Default

    A few points:
    Firstly, don't change the tubes unless they are non-functioning. Even if old, they will still probably produce output within a dB or so of new. Keep thrashing them until they fail!

    The suggestion about using a wooden dowel sharpened down:
    You may be lucky, but the neutralizing cap in mine was so stiff to turn the dowel tip would have broken off. DO NOT use a metal screwdriver even if it has a plastic handle - it would be easy to short something to chassis and cause a lot of damage. Use the correct tool or adjust in tiny increments then check.

    Neutralizing:
    I have used another receiver with the AGC off, this was a good way to detect minimum RF leakage. Lash a 50 ohm-ish resistor (12 volt lamp?) across the output with the SG off and trim for lowest carrier. (RX in SSB or CW)

    I have also used a 'scope - mine is a 20MHz dinosaur but was still quite capable of displaying a trace at 28MHz. You don't need one specified for the frequency - you are only minimising the reading, not measuring it.

    Good luck, and keep the old hybrids a-hummin'
    ...
    Andy.

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