"R. Ton" <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Well... I think I've convinced myself that this is normal behavior in
the T-4XC.
My "solution" was to key the PTT line through an MJE350 transistor --
this appears
to work.
I went over the Vox circuit and T/R relay keying circuit with a scope
and everything
seems to look right to my naive eyes. The PTT line from the microphone
is injected
into the Vox circuit at the junction of R68 and R69 if I read the
schematic right --
two 1 meg resistors. The values in that circuit lead me to believe that
we're dealing
with very low current levels. With PTT "open" this junction sits at
about -10V and
it takes very little resistance to ground to raise it enough to switch
V10B and engage
the relay.
In my switch box, I feed a single microphone / PTT switch to three
different rigs
via a simple rotary switch. The box also contains a K1EL solid state
keyer and
the 2N2222 PTT output of the keyer is also fed into the PTT mix. This
provides
enough resistance (about 2.1 meg) to key the T-4XC. Adding the MJE350
buffer
raises this enough that the PTT is now working like it should -- I now
treat it like
a grid-block key input.
That said... maybe one of you guys who routinely has a T-4XC on the bench
can run a little test and see if you can key it into transmit with a
high value (1 meg?)
resistor.
The good news... after playing with this stuff for a year or more, I've
learned a bit,
and the C line is now ready for some on-air use. :)
73 es thx for being there!
-Rob / KFØRT
"R. Ton" <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Thanks...
So far, that doesn't appear to be the problem. In my T-4XC the Vox
tube is a 6FQ7. I
swapped it with the 6FQ7 in my "parts" rig and also with a 6EV7 in my
TR-4C. All three
do the same thing. Interesting, though... None of these rigs has an
original Sylvania tube
for the vox. They've all been swapped out before at some time. This
makes me wonder if
this might be a common problem.
73, Rob / KFØRT
Richard Joey Fiero II W5TFW wrote:
I am no tech, however I just had that problem, weak vox tube 6ev7
Joey
all I had to do was touch mine,
Richard Joey Fiero II
W5TFW EM-40
QSL Manager USS KIDD W5KID
Director 6 Club www.6mt.com
----- Original Message ----- From: "R. Ton" <[EMAIL PROTECTED]>
To: "Drakelist" <[email protected]>
Sent: Sunday, February 18, 2007 1:38 PM
Subject: [drakelist] T-4XC Sensitive PTT
"R. Ton" <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Hello list,
I'm in the final throes of bringing my C-line up and have run into an
oddity with the PTT line. It takes almost NOTHING to put the T-4XC into
transmit. If I put my DVM across the PTT line and ground, it goes into
transmit. I can simply touch the PTT line with my finger and it goes
into transmit.
If I plug my D-104 in, all is well, but if I plug my (homebrew)
microphone switcher in, the rig goes into transmit even though the PTT
line is unkeyed -- it's hooked to a Heil foot switch. VOX is turned
off, but seems to function normally.
Any ideas on what might cause this?
TIA & 73, Rob (KFØRT)
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