From: "Al Parker" 
Subject: Re: [drakelist] Quick T-4x CW question


Hi George,
    That's a problem that seems to plague most of us at one time or
another.  The most often problem, other than mis-adjustment, is a gassy
6EV7.  For adjustment, the manual says to increase the vox gain until the
relay pulls in (and stays), then adj. the vox delay (on the rear) so it
drops out after a delay to suit you.  Your beginning statement, plate
current at abt .09a  -- the relay has operated with the key up, you may
have a little carrier which is driving the finals above the .07 bias
setting.
    The relay control in these is in an unexpected manner, there's an
audio oscillator (sidetone generator) and the key directs that signal to
the 6EV7. It has 2 triode stages, the first an amp, the 2nd gets a
rectified signal and drives the relay.  There's a spike generated at key
closure to drive the relay closed instantly at key-down, that's what makes
it click & release if it doesn't hold in.  The grid ckts, particularly the
2nd one, are high impedance, and almost anything that's not too normal
will upset it.  Things that can do it - the bias supply having ripple, the
LV supply having ripple, the cathode resistors for the 6EV7 off value,
leaky bypass or coupling caps, bias voltage not set right, and probably
more that I can't remember at the moment.  Some have suggested using a
zener diode in the cathode(s) to provide a fixed bias.
    6EV7's aren't real common, and DrakeMods suggests:  "A 6AQ8 will
replace the 6EV7 if a 47 ohm 2 watt  resistor  is  added across pins 4 and
5 of V10. The tube change is applicable across the entire  4  line  (and
TR3). The resistor IS NOT needed in any of the transceivers. Just swap the
tube, in this case."
    I'm presently trying to nail down the same trouble in a T-4XB.
Sometimes it'll work fine for a while, then will do as yours does.  I have
3 6EV7's I've tried out, one is brand new old stock.  All test a little
gassy on the Hickok 6000A (why do 6EV7's seem to be so prone to that?).
The new one's the best.  Any will work for a while at least.  I'm checking
 ripple on 2 AC-4's, that could be part of my problem.  i"ve checked ckt
component values, all look OK, but need to do a good ck on several caps.
    I hope this helps you some.
73,
Al, W8UT
New Bern, NC
BoatAnchors appreciated here
http://www.thecompendium.net/radio/
http://www.hammarlund.info


----- Original Message ----- 
From: "George KB2Z" 
To: 
Sent: Sunday, January 25, 2004 7:37 AM
Subject: [drakelist] Quick T-4x CW question


> Good morning all,
>
> I have a quick T-4x CW question.
> I'm new to the Drakes and this question might seem a bit lame, but here
goes.
> When in CW mode the meter reads about +/- .09A with the key up. (bias
set
> to .07)
> There is no output unless the tx is keyed
> Is this normal, (.09A) or is the relay hanging? I dont hear it cycling.
(
> Meter at 0, in SSB unless PTT)
> When I try adjusting the vox it sounds like the relay kicks on and off,
> very fast, when keyed ( output goes up and down fast with relay)
> The meter reads 0, before and after the relay cycles after playing with
> vox, but clicks on and off to fast to transmit.
> Thanks in advance for any input, advice, or suggestions,
> George KB2Z
>


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