Neutralizing 6146 tubes

Discussion in '"Boat Anchor" & Classic Equipment' started by W4JJA, Jun 5, 2010.

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  1. W4JJA

    W4JJA Ham Member QRZ Page

    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.
  2. KA4DPO

    KA4DPO Premium Subscriber QRZ Page

  3. WB5WSV

    WB5WSV Ham Member QRZ Page

    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. GM4CID

    GM4CID Ham Member QRZ Page

    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. AI3V

    AI3V Ham Member QRZ Page

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

  6. WD0GOF

    WD0GOF Ham Member QRZ Page

    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. W5RKL

    W5RKL Ham Member QRZ Page

    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:

    or from Kenwood's website at:\TS-530.pdf

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

  8. KM1H

    KM1H Subscriber QRZ Page

    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.

  9. MW0UZO

    MW0UZO Ham Member QRZ Page

    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. M0WAN

    M0WAN Ham Member QRZ Page

    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.

    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' :)
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