Hi Damien:

Yes, especially when replying to posts, be sure to note where the reply is directed address-wise. Always good to copy the list as well as any direct message so others can follow along with the discussion responses.

The scenario Garey outlined is very likely indeed. It kind of was an extension of my comment about it is sometimes hard to tell exactly what was going to happen in all stages of the rig. He went into the schematic a little deeper than I did--All of those guys are very knowledgeable in the Drake line-up.

If you plan to do much work at all on these rigs, Garey's CD with annotated pictures and notes is the best available as far as I know.

Hopefully, you caught it before the finals or other parts got damaged.

BTW, a fan pulling air out of the back of the cage is a great benefit to these rigs to shed some of the heat. That being said, these things will run 24/7 at rated output in tough modes like RTTY and just keep going--they are very robust as long as properly loaded.



On 3/13/2014 11:20 AM, Damien Mannix wrote:
Hi Curt,

Thanks again.  I will do everything you suggest.

Actually I am puzzled myself as to how the list works nowadays! I did in fact also hear from Mike Bryce (no call sign given), Evan K9SQG and Gary K4OAH who also kindly invited me to join the DrakeRadio group. Never knew it existed but I will certainly join.
Damien G3XER

Date: Thu, 13 Mar 2014 11:07:11 -0500
From: cptc...@flash.net
To: damienman...@hotmail.com; drakelist@zerobeat.net
Subject: Re: [Drakelist] What have I done now?

Hi Damien:

Doesn't change my thoughts really. Even tho the relay for Tx would not be engaged, and this keeps the cathodes floating and not grounded, with bias very low or removed from the grids, the tubes will conduct enough to get hot for sure. I think the worst is that the current comes thru the grids so can physically damage the tube internals.

Which tubes, finals or driver, or others, is a guess only--perhaps all to some degree. I would just power it up again with a full on AC4 and monitor it closely to be sure nothing has gotten burned or out of tolerance enough to do damage. Especially, confirm that the bias control does what it is supposed to do with adjustment range, verify that the current reading of plate current is close (be careful!) and do an operational check-out.

These are very robust rigs but the finals are especially intolerant of unloaded or excessive plate current being that they are TV sweep tubes.

Let us know how it goes. Kind of surprised we haven't heard from anyone else on the list.


On 3/13/2014 10:31 AM, Damien Mannix wrote:

    Hi Curt,

    Thank you for your two replies.  I am most grateful for your
    input.  How one can be misled.  I certainly thought I was doing
    the right thing!

    No sure if it makes any difference to your conclusions but I never
    switched to transmit I just left the TR4 in Receive mode.



    Date: Thu, 13 Mar 2014 08:25:26 -0500
    From: cptc...@flash.net <mailto:cptc...@flash.net>
    To: drakelist@zerobeat.net <mailto:drakelist@zerobeat.net>
    Subject: Re: [Drakelist] What have I done now?

    Thinking about it a little more, since it may or may not have
    transitioned to TX, the driver or any of the other tubes that are
    bias controlled can do the same at reduced voltages.

    Hope there was no long term damage.

    I once worked on a FT101E that had a defective socket on the grid
    of one of the finals.  As soon as HV came on, with that grid
    floating, it began cooking.  Bias measured OK, all voltages
    lookedOK, but no bias was getting to the actual tube--duh!  I
    finally figured out what was going on after the tube got so hot,
    the vacuum sucked a hole thru the side of the tube.  Still have
    that tube BTW...reminder..


    On 3/12/2014 12:18 PM, Damien Mannix wrote:

        Hi all,

        Still waiting for better weather to put up an antenna but then
        ready to go with my TR4/AC4 which are fine into a dummy load,
        or at least they were!

        Bought a, supposedly good, AC4 as a spare.  Decided to power
        it up gradually with the TR4 as a load. Two hours at 50v, two
        at 80v, two at 110v, two at 140v.  No problems and a fan on
        the rear behind the PA begins to run at this voltage.  Then,
        ten minutes at 170v and 'wow' what is that smell?  I thought
        it was my shack heater.

        No it was the TR4.  The top, above the forward most PA tube,
        was unbelievably hot.  Switched off immediately of course.

        Can't spot anything untoward in the PA compartment so after a
        complete cool down I took it slowly up to 230v with my usual
        AC4.  Not done a full test but it seems perfectly happy again,
        heat and smell wise, after 30 minutes at 230v.

        Might I have ruined anything and, presumably, the fault is in
        the AC4.

        Thanks in advance for any thoughts.


        Damien G3XER

        Drakelist mailing list
        Drakelist@zerobeat.net  <mailto:Drakelist@zerobeat.net>

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