Amps
[Top] [All Lists]

Re: [Amps] Requesting opinions on a Drake L-4b's tubes

To: David Gow <6146guy@gmail.com>
Subject: Re: [Amps] Requesting opinions on a Drake L-4b's tubes
From: John Lyles <jtml@losalamos.com>
Reply-to: jtml@losalamos.com
Date: Sun, 25 Dec 2022 14:28:20 -0700
List-post: <mailto:amps@contesting.com>
The Collins 828C1, and Continental 314R1 1kW medium wave transmitter used a single 3-500Z as a switch tube running at 70 KHz switching frequency for pulse width modulated AM. It was very picky of the type of tube, and required component changes if switching to a graphite anode tube to prevent disasters. So apparently there are differences in the tubes. Maybe not subtle when paired in parallel in ham amplifiers?

http://www.jtml.info/

73

John

K5PRO

On 12/24/22 11:27 PM, David Gow wrote:
The original poster said they were in original Drake packaging.  If they were in fact in original sealed Drake boxes I wouldn't worry about using them together as Drake would have sold them at different times as compatible spares.  I have mixed all sorts of 3-500z tubes in many amps over the decades and my test is to see if under color if the look about the same they are ok to use together.  Your are correct in theory but perhaps not so much in practice.  Right now my Henry 2K3 has one original NOS stock Eimac from my shelf bought by me over 25 years ago and a brand new RF Parts Chinese graphic tube.  THey were both unused when I installed them six months ago.  They show about the same color, a nice  dull red. when appropriate and have normal plate current, grid current and put out about 1200 watts on 20 meters.  Best practice?,no,  but works fine.  My buddy, a retired broadcast engineer, doesn't approve either so I told him to buy me a nice new matched (at least for a few hours!!) set.

On Sat, Dec 24, 2022 at 8:14 PM John Lyles <jtml@losalamos.com> wrote:

    The author originating this discussion said that they had one 3-500Z
    that was the vertical thin fin plate, Eimac original, and one 3-500G
    that has the graphite anode presumably with the horizontal heat
    radiating structure. This would look like the Amperex/Covimag
    tubes that
    are no longer made, but are cloned in China. For that matter, the
    original 3-500Z from Eimac is long out of production as well.

    I think it would be more risky to pair these two tubes together as
    they
    come from different manufacture with different plate physical design.
    There is no guarantee that the cutoff bias voltage is identical
    and that
    the mu is the same or within a tolerance. Operating this way might
    cause
    one tube to hog more current, have higher dissipation due to the
    idling
    current (Zsac), if they both share the same cathode bias setting.

    It would be optimal to put the older style NOS tube into the
    amplifier
    with one of the original (weak?) tubes to see if it works better.
    Then
    try it with the other original tube. If the two tests show large
    difference in power capability, then I would suspect just one of
    the old
    tubes. At least start with this plan, and see how it works, report
    back
    here.

    If anyone is interested in Amperex/Covimag 3-400Z or chimneys for
    either
    triode, get in touch.

    73 and Happy Holidays

    John

    K5PRO

    _______________________________________________
    Amps mailing list
    Amps@contesting.com
    http://lists.contesting.com/mailman/listinfo/amps

_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
<Prev in Thread] Current Thread [Next in Thread>