From: "Ken, WA2LBI" 
Subject: Re: [drakelist] TX4C Power Output problems


"Ken, WA2LBI"  made an utterence to
the drakelist gang
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Larry,

The loss of power could be weak finals or driver but let's look at the quick
drop out problem first. The sidetone generator sounds like the culprit for this
quick drop out when in CW mode. This can also be caused by setting the anti-VOX
too high. These rigs are not keyed directly in transmit mode. An audio
oscillator (sidetone generator) output is keyed and sent to a 6EV7, V10, I
believe (I don't have the road map in front of me). It has 2 triodes, the first
is an amplifier, the second gets a rectified tone signal and drives the T/R
relay.

A spike is generated at key closure that drives the relay closed instantly. This
is what causes it to pull in and immediately drop if the rectified tone signal
is not sustained. There are several causes for this problem such as ripple on
the bias supply voltage, improper bias voltage, ripple on the low voltage,
wrong value (aged) cathode resistors for the 6EV7, a gassy or otherwise
defective 6EV7, and a few more I can't recall at the moment. You said your
friend saw that "the signal drops off as it enters the tube". It
looks like a
good place to start.

Let us know what you find. Good luck!

Ken, WA2LBI

Quoting Larry Groom :

> I just aquired a TX4C that is having some quirky problems. When I put the
> transmitter into
> the Tune mode after it's tuned, the power will jump to 100 watts and then
> drop down to 60 watts
> after approx. 10 seconds. If I then tweak the gain control to a higher
> postion (ie move CW) the power
> will return to 100 watts and stay there. I've taken the rig to a friends
> house who's very sharp on these
> tube types. After poking around he discoved that the problem may be in the
> sidetone generator circuit.
> He was able to see that the tune signal drops off as it enters the tube
> (can't remember the tube number)
> and I was also told the my mic. audio was getting distorted as I was using
> it. (I imagine if I had increased gain
> in may have come back) Also, when I tried to use the rig in CW mode the rig
> would go into transmit mode and
> then drop out quick, just a beep and back to receive, irregardless of VOX
> setting.
>
> Has anyone had this type of problem or any ideas?
>
> Larry W0FLY
>

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